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nt
THE
VELIGER
A Quarterly published by
CALIFORNIA MALACOZOOLOGICAL SOCIETY, INC. Berkeley, California
R. Stohler, Founding Editor
Volume 26
July 1, 1983 to April 2, 1984
TABLE of CONTENTS Number 1 (1 July 1983)
Our thanks to Rudolf Stohler. R. I. SMITH New molluscan species (Gastropoda: Neogastropoda) from the tropical eastern Pacific. LEROY H. POORMAN The biology of the northeastern Pacific Turridae. III. The habitat and diet of Kurtziella plumbea (Hinds, 1843). R. L. SHIMEK 10 Flow through and around the abalone Haliotis kamtschat- kana. ASNIGEBVIOUMZOW! Gigah cee oo as ke neil ee es 18 Shell strength in Corbicula sp. (Bivalvia: Corbiculidae) from the Potomac River, Maryland. VicTOR S. KENNEDY AND JAY A. BLUNDON .... 22 Relationship between beak morphometrics and live wet weight of the giant Pacific octopus, Octopus dofleini martini (Wilker). SHAWN M. C. ROBINSON AND E. BRIAN HARTWICK . . v6. a0. aa Os ed faked op ad ce Sra ne ee 26 Studies on the reproductive biology of some prosobranchs from the coast of Pakistan bordering the northern
Arabian Sea. II. Egg capsules and larvae of four species of Thais. SOHAIL BARKATI AND MUZAMMIL AHMED 30 Comparison of northern and southern populations of Ep- itonium tinctum (Carpenter, 1864) on the California coast. CaREY RESCH SMITH AND AMY BREYER 37 The reproductive cycle of the trochid gastropod Oxystele variegata (Anton, 1839). M. A. P. JoskA AND G. M. BRANCH.......... 47 The larval biology of Brachidontes modiolus (Linné, 1767) (Bivalvia: Mytilidae). ANGELA FIELDS AND EUNA MOoRE 52 A comparison of the species richness and trophic roles of gastropods and chitons on rocky shores of temperate and tropical west America. ENILNN (Gi, IMOTUUTY slog ao soe ooudvianoay ooo gesn 62 Range extensions of three opisthobranch mollusks to the San Diego—La Jolla (California) Ecological Re- serve. Hans BERTSCH AND TOM SMITH.............
Number 2 (3 October 1983)
Radular patterns, systematics, diversity, and ecology of deep-sea limpets. CAR OUEBS MENCKMANE ane ceisc lair s skeen 73 Additions to the opisthobranch mollusk fauna of Marin County, California, with notes on the biology of cer- tain species. WILLIAM B. JAECKLE 93 Specialized feeding in mitrid gastropods: evidence from a temperate species, Mitra idae Melvill. ALLAN FUKUYAMA AND JAMES NYBAKKEN...... 96 Homing in the West Indian chiton Acanthopleura granu- lata Gmelin, 1791. DAVID ENT OOK eee ecieib ye Actin ssh nd alee eens 101 Aspects of reproduction in some enoploteuthid squids from Hawaiian waters. LIGA IME, JE\OW CSI vers bao os om Oe gee ome oe 106 Shell repair frequencies of two intertidal gastropods from northern California: microhabitat differences. A ONATHANEBS GBLELERMM a ae ane aor lS Morphological divergence and predator-induced shell re-
il
pair in Alia carinata (Gastropoda: Prosobranchia). Jutta BERGMAN, JONATHAN B. GELLER, AND VICTOR
CHOWMAAE fasts ee eee EAE Nes cements 116 Thermal effects on some mangrove mollusks. Honc Woo KHOoo AND ELEANOR CHIN ....... 119
Barnacle attachment on live Nautilus: implications for Nautilus growth rate. NeIL H. LANDMAN 124 Distribution and abundance of Caecum cornucopiae (Gas- tropoda: Prosobranchia) on Cladophora crystallina mats in a Bahamian salt water lake. BESTS YD) Aas ape erates Mak pre Soterek ee, fy seal kee geet 128 The Bermudan and Caribbean sacoglossan mollusk Elysia flava Verrill now recorded from the Greek Aegean Sea.
PIE H OMPSON Per pea ceva oocytes ae 136 Do oystercatchers influence limpet shell shape?
P. A. R. Hockey aNnD G. M. BRANCH ........ 139 A range extension of Nassarius miser (Dall, 1908).
IROBERM Iss EIOWLEY arse as) terior Shee oer 142
Number 3 (3 January 1984)
Activity, dispersion, and size of Lanistes nyassanus and L. solidus (Gastropoda, Ampullariidae) over the depth gradient at Cape Maclear, Lake Malawi, Africa.
S. M. Loupba, K. R. McKaye, T. D. KOCHER, AND C. J SSTACKHOUSE snot ee eee 145
The Recent Crassatellinae of the eastern Pacific, with some notes on Crassinella.
EUGENE COAN 153
Description of five new species of Hawaiian Eulimidae.
ANDERS WAREN, BEATRICE L. BURCH, AND THOMAS A. BURCH 170
A new species of Ischnochiton (Mollusca: Polyplacophora) in the Gulf of California.
ANNINONNO) JJo JONNY, 6 occ 0cso0ccv0ss00as oc 179
Records of Cuthona pustulata (Alder & Hancock, 1854) from the Canadian Pacific.
TERRENCE M. GOSLINER AND SANDRA V. MILLEN... Ee Ae eee eee ey ernest PY chats, Sh ga 183 The ecology of Parvilucina tenuisculpta (Carpenter, 1864)
(Bivalvia: Lucinidae) on the southern California bor- derland. GILBERT F. JONES AND BRUCE E. THOMPSON... 188 Hybridization of two populations of a marine opistho- branch with different developmental patterns. HiLitary H. WEstT, JUNE F. HARRIGAN, AND SIDNEY
K.. PIERCE. ..< 250. 409505005500 ee 199
The opisthobranch mollusks of Humboldt County, Cali- fornia.
WILLIAM BS JJAECKILES 35 a0 6 ooo eee 207
Doridacean nudibranchs from Sri Lanka, with descrip- tions of four new species. NATHALIE YONOW 214 Technique for narcotizing and fixing veliger larvae of Am- phibola crenata. PENNY STIRLING, COLIN LITTLE, MARGARET C. PIL-
Number 4 (2 April 1984)
Supplementary information on the morphology of Phes- tilla melanobranchia Bergh, 1874, from Seto, Ki, Middle Japan (Nudibranchia: Aeolidacea: Tergipe- didae).
ISIKUMARO BAB AGS a5 o/c cae Oise ey ais ee era ee 241 Distributional records for terrestrial and freshwater Mol- lusca of the Cascade and Coast ranges, Oregon. BRANLEY ALLAN BRANSON AND ROGERS MACGOWAN
BRANSONEY a Potton ye eae eee ene ee 248
The biology of the northeastern Pacific Turridae. IV. Shell morphology and sexual dimorphism in Aforia circi- nata (Dall, 1873).
IROINIALID) Ik, SIBUIMIDK occ ounscc vende ceuccsve ce 258
Distribution and radular morphology of various nudi- branchs (Gastropoda: Opisthobranchia) from the Gulf of California, Mexico.
Hans BERTSCH AND ALEX KERSTITCH ........ 264 The diets of Alaskan Neptunea. IRONALEDEIL SHIMEK@s ay Athy score ee eee yak
Spatial distribution of three species of bivalves on an, in- tertidal flat: the interaction of life-history strategy with predation and disturbance.
Mark L. BOTTON 282
Orientational and anatomical trends related to detorsion among prosobranch gastropods.
1V
KINGTON, AND JOHN B. PILKINGTON....... 229
New species of northeast Pacific archaeogastropods. JAMESTEIRI MICIZRAN Ia Aen eee eee 233 Louis F. GAINEY, JR. AND CHARLES R. STASEK ..... uygiey sao ee a ee ae ee 288
Reproductive cycle of Anomia simplex (Pelecypoda: Ano- miidae) from Cape Cod, Massachusetts. DD IANED py BROUSSEAU Se eee 299 Influence of varying oxygen tension on the oxygen con- sumption of the freshwater mussel Lamellidens mar- ginalis (Lamarck) and its relation to body size.
V. Mapan Mouan Das aNnp S. A. 'T. VENKATACHARI 305 Gaimardia bahamondei, spec. nov., from central Chile (Mollusca: Bivalvia: Cyamiidae: Gaimardiinae).
CECILIA OsoRIO R. AND PaTRICK M. ARNAUD .. 311 Egg masses and larvae of three species of Cerithium from the Arabian Sea. SOHAIL BARKATI AND MUZAMMIL AHMED 316 Male reproductive system of Chorus giganteus (Lesson, 1829) (Muricidae: Prosobranchia): anatomical and histological description. MartTaA AMin V., IRENE LEPEZ G., OSCAR Marin S., ASNID) IMUASTA, IDISIUAIN| Na op oc op uve as eeaace 320 Anesthetic methods for the moon snail Polinices lewrsit. GEORGE B. BOURNE 327 An earlier name for Nassarius corpulentus (C. B. Adams, 1852). RICHARD E. PETIT
AUTHOR INDEX
TIMID DNAS eerie ocr os Pe oo Aa eRe 30, 316 ENINSTONT,, Wo HINA Li ie Viet clea: eh Sn Bec a 320 AARRINUNTUID),: 12, JNA latounir te ene ete etna ota euoica a penen (cess mene 311 IBVAIBVA, UEC V2 Gralla et Rete: 6 SISGUrt non ee dice ree anes tae ar sere wueme 241 TBYAIRIRATI Ls Sig aks See Gace Been cee uence Gkencnc trie atone 30, 316 {BUST GINAUAINYS »| feaulnana eate-cnel es come tre ook ve ais yee teeanee nae 116 IBERINSCHA@EAR te me cass Ga whe eile taunts ocr 69, 264 BEWUNDONNG EY ACur Minty Sr arhees rn seein dd Sts 22 TBXOVITUROINT: NA La ya! oa ed a ees ee se eo 282 BOW CHER MMO M VIR Kin natin eater ein Wan Ae, he ae 106 BOURNE GB ges uaricih te ccttsurset tats ertla arava as 327 IBRANGHRE GINS, ey aiaccsn hoists ah os i Gaele dt 47, 139 BRANSON Dy ACH wa res ert 1a Aatiny a Js coma canes 248 IRAN © Neg Rem Lenraitre efits Sie ic telecine ele wes alia a 248 [BURTOWZTAIR, ANH al cece al RU ere Sere Be oe 37 BROUSSHAUS DEA Parents, welathacsiee a cuee sie sis en 3 299 WRC HBB olen tes ene eA eee 5 ole ee ues dodrsee sh 170 BWR CAME Ata Sle eGo auieie ts betes aon ana sa.s 170 (CRETE re ey tr oy OUR E A Gone UM eee Sena 119 (CHBIONY, Ws. a2: Bead eves rele Cone ee en ear 116 GOANRIE ee ee BA eae eee HS ti were oc 153, (232) IDAS, Wo IMIGUNG ei coereed aronetero nao tose chers cieeenet een 305 ID VAST, 1B)s: -o:ni bs abekor Ba siceeelee Seo E karen ceca enya ete tr aetna ean 128 1D) IARING ACMI ane enn inie sepcrtuneiaeneene hese atime oa os 320 HE RRETRA Nees mle Wart auer cnet aici Sei tis marek ei ss 179 IESIEVIATS) SMe Nagata ewes erent ere A ans 2 lieve tele, thio es os 52 TEAUIKSUWAN TA Nets str hee H Sety ie coe hese seg laneadg a 96 (GlATINTBN Ys, Las. 1 Be | RS" Soe) cepscltts ata Sache ciy oes tect le pane mre 288 (GIBILILIBIN | [o-IB3s ace chetonee eiguses ee encioe ae ecercaetaar™ 113, 116 (GOSTEINE Realy VIR es oe hu eons Hb koa lara eee 183 TRUATRIRIIGYAINT, - [ic] Se oe toa as basics ot aie Serer eee Sea ra 199 VARGA WiC Keen eta sleet Pyne eeu nese eset a ge ees eres = a 26 TEUIGRIMUNING: (Canty eck Sig co basics sare ok to Sen ee a ee W® VEU OGT RING) A) Re 139 LO WBE Ag Ee ed losin Sanu en cv terge CAN Sc ee hs 142 ASE CPE SAV VES Suir seer eictia ea che eectien: 93, 207 JOINTS, Gis TESTES axe choo Gola a eRe meee ene ae ne 188 A OSIKACEIN TEE Ace 2 sapere neta ara eases Sah ls Cl vate a8 47 TRANOOTESTS 7-91 De, lg eN is a Neer a ee ee (144) ISBNNEDYAIVES ont tie e ene is Bn deen Aa aa 22
IGERSMI CH SA oan came ase eaa Roetmionce ahs 2 264 IRHT OO SELES VN oie an Me een EMRE SE ie, ou thc et ied 199 IS @ CEE Route SO) 0 ears ell eee i aie gear Say ey By als 145 TEIN NUAIN Nea alison pera aitor creer ir Puree teor one ba cies 124 P74 G5. he en soe RS eres We eR vn Ho see 320 ISINDBERG wD RAGE aan ecauarir ity ses croes (334) TE TATeIGTA By OM ee ar ei oie Meee tee ees Ome eyes 229 TEOWD ALS NIG Cee ee ais wep oe eemuage eee MEMES ta ci ncee etn 145 INIVARITING St ©) sete cle ea as Rah a ge are ag ane a 320 IVI CIGARS RGe gio eee Soi rare ree a Nee ys 145 IMICIERAINGS Je bleu aiy) amen mec ten eon pasar casa nea 233 INAITTEICE: NERS 5 Weare cc miteee ts, maa tied cece eS ECs tare ePaee. 6 183 IMITTETIGE RE ACR Gin tee ae eins ore sash vee enare ns Ces Poe nto wrens 62 INALGYG) S155) B Yes een Ry ear eta Ran dR tl nie, th ntoN nl aac eH eter 101 INTOORE Bes ele Cer se entrar Np eReni gts, Ry we Weta beaters 52 INVIBAKIKENS Ji tas rosenusyoibae e mascara cae cla ete e 96 OSORIOBR GS Cie ee aula ere ye ase ac eae Sen 311 ] PDF UURIU a] Aan pray RENT ntetcer sem ok Le INST ae ale ere rete ned RO 330 | ES OCHO) aise De Sarna is ae rae aed Baca a eer (143) JEN TIO) Os) hor ena aa LOO VD me eu PEE Moa 199 RIEKING TONGS BS: ciate cee ath ube eiaasieee ela a 229 JPAGLISTINIGARON IML, Choco coeeannadcedsaccnscovuce 229 IROORINGAN Se ele Ava ee eames te pert are veers evar 5 INOBINSO Nags tales Cease ane nea ene 26 ROTHER B: Bie Scars Mieniea aac hee ates (143), (332) ISHIIMIR. Ke RES SIGS ioe tripe se eget Sista oaet nareas 10, 258, 274 IS MOTIDET a GROG ais oe a Oe el -mn RC EL ppe Nagra ee 37 S MINISEIERIRGOD oe toh, rere oe eee mer erate repent ee Ace 2, SMITE abl suetonttc penny eae aa ie SET Ae ae ee ine Scare el 69 STACKHOUSEMC A Wis rarest ean res ego ites ee Aevent aes 145 SIRASEK ti Ge Reais a elenyay Ye aiden Seu nnu mn myteN circ cum ee 288 SRIRIEING SiR aaretye eee Ln sien Syn anaiie co Lrer ene 1a 229 AHONMPSON a Bina a ees, este Wien ae irae 188 ATISCOWM IASON Men Bs sve, ga, Seto a peemae lore bouts oeeea neuer amee 136 WIDINTYNIPNGTEIN, Ss A Ws coctonscocsauosucosue 305 VOTEDZ OWI To senate cuehoke ante wa gamete ta dececa 18 VVEANRIE: NA (as noes ennara ihe Be depot err Maerua At, 170 DV VSESSoie ole] a El oar erras secant beurre mn crane SUN esc dmc ae 199 VION OWAN Nik eee re entender tie pert ns Sinuta ke 214
Page numbers for book reviews are indicated by parentheses.
GW, pie ISSN 0042-3211 SYSNTION 4O NOISIAIC
THE, = wasvesi toticcs
% (IV H WITHA
VELIGER
A Quarterly published by
CALIFORNIA MALACOZOOLOGICAL SOCIETY, INC. Berkeley, California
R. Stohler, Founding Editor
Volume 26 July 1, 1983 Number 1
CONTENTS
Our thanks to Rudolf Stohler
Pap Ie OVNI Mee weep ae nee OSI AMM ta ice ie aout fel Bt adele a als 2 New molluscan species (Gastropoda: Neogastropoda) from the tropical eastern Pacific RO Napisy e OORINVAING eyes tet cae ore Yap cf wean toy al hen es, sy aa ev nie aha IS Imei euege Ye olle 5
The biology of the northeastern Pacific Turridae. III. The habitat and diet of Kurtziella plumbea (Hinds, 1843) [Re Lia, STEMI TSC FG tha louse seat teades Aas remain at te ADs RRO Pete na ok Raat e non 10
Flow through and around the abalone Haliotis hamtschatkana SAINI EMV OIMGZOW paar les icie re yh he aoee aired ese ay ee cis SUTIN, A UR ee at Be 18
Shell strength in Corbicula sp. (Bivalvia: Corbiculidae) from the Potomac River, Maryland WiICTORE SIKENNEDYSAND EJAY. Ac IBISUNDON) 2 qe) fst cele) ah neater 22
Relationship between beak morphometrics and live wet weight of the giant Pacific octopus, Octopus dofleini martini (Wilker) SHAWN M. C. ROBINSON AND E. BRIAN HARTWICK ................... 26
Studies on the reproductive biology of some prosobranchs from the coast of Pakistan bordering the northern Arabian Sea. II. Egg capsules and larvae of four species of Thais SOEATION DS AIRIKCASInIe ANID) BV MUHA MIN OTIS NEUE) es) oe SARE ee eee 30
CONTENTS — Continued
The Veliger (ISSN 0042-3211) is published quarterly on the first day of July, October, January and April for $18.75 for existing members (plus mailing charges) and $37.50 for libraries and nonmembers (plus mailing charges). Mailing charges for all domestic addresses are $3.25 and $6.00 for all Canada, Mexico, and foreign addresses. Further membership and subscription information appears on the inside cover. The Veliger is published by the California Malacozoological Society, Inc., % Department of Zoology, University of California, Berkeley, CA 94720. Second Class postage paid at Berkeley, CA and additional mailing offices. POSTMASTER: Send address changes to C.M.S., Inc., P.O. Box 9977, Berkeley, CA 94709.
THE VELIGER
Scope of the journal The Veliger is open to original papers pertaining to any problem concerned with mol- lusks.
This is meant to make facilities available for publication of original articles from a wide field of endeavor. Papers dealing with anatomical, cytological, distributional, eco- logical, histological, morphological, physiological, taxonomic, etc., aspects of marine, freshwater, or terrestrial mollusks from any region will be considered. Short articles containing descriptions of new species or lesser taxa will be given preferential treatment in the speed of publication provided that arrangements have been made by the author for depositing the holotype with a recognized public Museum. Museum numbers of the type specimen must be included in the manuscript. Type localities must be defined as accurately as possible, with geographical longitudes and latitudes added.
Very short papers, generally not exceeding 500 words, will be published in a column entitled “NOTES, INFORMATION & NEWS”; in this column will also appear notices of meetings, as well as news items that are deemed of interest to our subscribers in general.
Editor-in-Chief David W. Phillips, 2410 Oakenshield Road, Davis, CA 95616, USA
Editorial Board
Donald P. Abbott, Emeritus, Hopkins Marine Station of Stanford University Hans Bertsch, Universidad Autonoma de Baja California
James T. Carlton, Williams College—Mystic Seaport
J. Wyatt Durham, University of California, Berkeley
Cadet Hand, University of California, Berkeley
Carole S. Hickman, University of California, Berkeley
A. Myra Keen, Emerita, Stanford University
Frank A. Pitelka, University of California, Berkeley
Peter U. Rodda, California Academy of Sciences, San Francisco
Clyde F. E. Roper, National Museum of Natural History, Washington Judith Terry Smith, Stanford University
Ralph I. Smith, University of California, Berkeley
Wayne P. Sousa, University of California, Berkeley
T. E. Thompson, University of Bristol, England
Alex Tompa, University of Michigan, Ann Arbor
Membership and Subscription
Membership in the California Malacozoological Society is open to persons (no institu- tional memberships) interested in any aspect of malacology. Annual dues, which include a subscription to The Veliger, are US $18.75 plus mailing charges. An initiation fee of US $2.00 is required of new members; a reinstatement fee of US $1.00 will be required if membership renewals do not reach the Society on or before April 15 preceding the start of the new Volume. If a receipt is required, a self-addressed, stamped envelope (or in the case of foreign members, the envelope and two International Postal Reply coupons) should be included with the membership or subscription request.
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TO OUR READERS
The previous issue, Volume 25, Number 4, marked the completion of 25 years of growth and success of The Veliger, success due in great measure to the efforts of one man, Rudolf Stohler. The climb is by no means over. With Volume 26, Number 1, we begin again, advancing by standing on the shoulders of our predecessors.
Some changes in format and style will be apparent to readers of the current issue. Our journal is now being produced by Allen Press, a quality commercial printing house specializing in scholarly journals and books. And there is a new Editor. Prospective authors may wish to consult the revised “Instructions to Authors” printed on the inside back cover. There are some changes.
Despite these changes, our purpose remains the same. The California Malacozoological Society, through its journal The Veliger, remains committed to disseminating new information in the field of malacology and conchology as widely as possible at the lowest cost possible. We likewise reaffirm our continuing commitment to meeting ever higher standards for the publication of scientific information.
There is no reason why The Veliger should not continue to grow for another 25 years. Our Society is vigorous and healthy. However, ominously escalating costs of publication have already threatened many a once healthy society. The simple truth is that we will need increased levels of income to balance our increased production costs. Readers can help ensure the continued publication of The Veliger by joining the Society (or by renewing their membership) and by encouraging their local and University libraries to subscribe. Donations are, of course, another extremely important means of ensuring the success of our Society (contributions to CMS are tax deductible).
A new beginning is a time to reaffirm our purpose, to acknowledge the many splendid contributions that have brought us this far, and to seek ways to improve. The new Editor asks you to support the Society and invites the comments of readers, members, and prospective authors. He looks forward to serving you.
D. W. Phillips, Editor
Photograph by Leroy Poorman
RUDOLF STOHLER
OUR THANKS TO RUDOLF STOHLER
With the completion of Volume 25 of The Veliger, Dr. Stohler has retired as Editor—stepping aside for some well- earned rest while still able to help us with his counsel and to inspire us with his unabated interest and enthusiasm. It is a good time to look back over the history of The Veliger, and to reflect gratefully how much we owe to the efforts of one devoted individual.
To many who have read and contributed to The Veliger, Rudolf Stohler may be simply an exacting Editor, a stickler for accuracy and good order in writing; to those of us who from time to time have transgressed, he is one who can communicate in pithy language; to those of us who have appealed for help, he has been ready with advice and assistance. But Rudolf has done much more than found and edit The Veliger, and we should fill in the picture of his pre-Veliger years, for information on which we are indebted to Professor Emeritus Richard Eakin, long-time Chairman of the Department of Zoology at the University of California, Berkeley.
Rudolf Stohler earned his Ph.D. at the University of Basel in his native Switzerland, and in the period of 1926-1932 published a series of papers on the chromosomes of European toads and their ovaries and Bidder’s organs. He came to California in 1928 as a Rockefeller Fellow to work with Dr. K. F. Meyer at the Hooper Foundation on the University of California’s San Francisco campus. The first day, as he arrived at the laboratory early, as was and is his habit, he picked up a large beetle that aroused his zoological curiosity. A young lady coming to work offered to obtain a bottle for the specimen. The Fellow was impressed with her kindness and friendliness and decided, then and there, that he wanted her for his wife. A year later Genevieve and Rudolf were married.
Dr. Stohler had expected to continue his study of sex determination and differentiation in amphibians, but Professor Meyer had other plans for him, namely, that he work as an assistant on paralytic shellfish poisoning. At first it appeared that diatoms, found in abundance by Stohler in the guts of mussels and clams, might be the source of the lethal poison. Without more evidence Professor Meyer immediately published a paper, as sole author, to that effect. Later, Dr. Stohler disproved that hypothesis. The source of the toxin was found to be Gonyaulax or other red tide flagellates that are eaten by the bivalves.
After the.completion of the fellowship, the Stohlers emigrated to Switzerland, but as the climate was unsuitable for the young bride the couple returned to Berkeley in 1932. Dr. Stohler was appointed a Research Associate (an honorary title but without salary) by Professor C. A. Kofoid, then Chairman of the Department of Zoology, University of California, Berkeley. Again Dr. Stohler was not free to pursue his own research because he was assigned to projects of Kofoid’s. To earn a living Stohler organized classes in German. Among his students were Alden Miller, later a Director of the Museum of Vertebrate Zoology, and Richard Eakin, later a Chairman of Zoology. In 1941 he was appointed to the position of Specimen Preparator and Collector for the Department of Zoology. In these capacities he ranged the California coast collecting for classes and for research, and developing a wide circle of friends and scientific colleagues. Later, under the Chairmanship of Richard Eakin, Dr. Stohler was relieved of some of his service responsibilities by appointment as a Research Zoologist (the research equivalent of a professorship) and was given an assistant and time to devote to his malacological interests.
Dr. Stohler has also had a career of teaching. In 1934 he gave the departmental courses in cytology and assisted Professor Kofoid in courses in protozoology and parasitology while Professor Harold Kirby was on sabbatical leave. For many years he gave courses in the University of California Extension Division in Oakland, San Francisco, and Berkeley. And he has generously advised graduate students and faculty on procurement of research material, on nomenclatural and taxonomic problems, and on scientific writing.
In the early 1950’s Rudolf Stohler and several colleagues of like interests founded the Northern California Malaco- zoological Club, the rather imposing name reflecting that the group was broadly interested in molluscan biology and not merely in “‘shell-collecting.” On June 27, 1958, appeared a mimeographed Club newsletter, ““The Veliger,” suitably named for an infant mollusc.
The new publication grew rapidly and by its fourth year contained 220 pages and had appeared in printed format— made possible because Stohler had, out of his own pocket, acquired and set up in his basement an old linotype machine. Over twenty years later, on this machine, now supplied with a dozen different type-faces, Stohler still regularly set type for The Veliger, which since 1967 has run to over 400 pages annually.
After many years’ investment of Stohler’s skill and labor, not to mention over $7,000 of his own money, The Veliger had clearly outgrown the needs of the Club and was incorporated by a small support group, the California Malaco- zoological Society, as a non-profit corporation. Stohler, with only a part-time business assistant and the help of various
Photograph by Jane Scherr; courtesy of “California Monthly.”
individuals (notably Mrs. Jean Cate), carried on all the essential functions of editing, printing, and distributing the journal, whose circulation is now over 800.
The corporation undertook to repay Stohler his $7,000 investment. But, in setting up the corporation, Stohler had instituted an endowment fund, the capital of which cannot be touched, but the income from which can be used to help support publication, for example, of papers with expensive illustrations that cost more than an author can afford. As fast as the corporation paid back installments on the debt, Stohler put the money into the Endowment Fund, to aid the publication (contributions to this fund have come from many friends and are, of course, still enthusiastically welcomed).
The success of The Veliger, which has never received a penny of foundation support, is a remarkable example, in this day of heavily-funded, group-supported ventures, of what one person with skill, energy, and devotion can accomplish. The first 25 volumes of The Veliger form a fitting and living monument, and it is our hope and intention that Rudolf will see it flourish for many years to come.
To characterize Rudolf Stohler as a person is not easy. Even more solid than The Veliger, Rudolf radiates energy and enthusiasm. Generally at the Zoology Department well before anyone else, Rudolf moves with a brisk, perhaps bouncy, style. Extremely helpful to those needing and seeking his help, and sympathetic to personal needs of students, Rudolf is yet one who does not suffer fools gladly. Above all, he detests sloppiness in anything, physical or mental. His choicest comments have been reserved for his favorite béte noir, the U.S. Postal Service, but others have not escaped. Yet all who have known Rudolf know that behind the sometimes pungent manner there lies a deep decency, integrity, kindness, and high personal standards. Rudolf has not lightly retired as Editor of The Veliger, and doubtless feels like many a parent watching his child venture out into the world. His principal concern is that The Veliger maintain high standards. To this aim the Executive Committee of the California Malacozoological Society and the new Editor are committed.
A final word needs to be said. In all his work for over 50 years Rudolf has had the support of his devoted wife, Genevieve, who has shared heavily in the labor and frustrations of producing The Veliger. Although inconspicuous in the background, she has nevertheless earned our deepest gratitude.
R. I. Smith
The Veliger 26(1):5-9 (July 1, 1983)
THE VELIGER © CMS, Inc., 1983
New Molluscan Species (Gastropoda: Neogastropoda)
from the Tropical Eastern Pacific
LEROY H. POORMAN
15300 Magnolia Street, Space 55, Westminster, California 92683
Abstract.
Three new species are described: Murexiella venustula Poorman, spec. nov., off the south-
ern coast of Isla Santa Cruz, Galapagos Islands, Ecuador, and probably the Gulf of California; Daph- nella levicallis Poorman, spec. nov., off Estero San Carlos, Sonora, Mexico; Anachis (Parvanachis) mullineri Poorman, spec. noy., in Bahia de Santiago, Colima, Mexico.
TWENTY-NINE YEARS of observing and collecting mollusks along the west coasts of the Americas has resulted in the recognition of a number of new species, eight of which have already been published. Three additional species are described herein.
Murexiella Clench & Pérez Farfante, 1945
Type species: Murex hidalgoi Crosse, 1869, by original designation.
The small, stoutly fusiform shell has four or more var- ices with foliated spines connected by a laminated web- bing. The siphonal canal is moderately broad and extend- ed. The operculum is muricoid, with a sub-apical nucleus.
Murexiella venustula Poorman, spec. nov. (Figures 1, 2, 5)
Description: The shell is small and solid, consisting of five whorls and a turbinate protoconch of three turns. Axial sculpture is of seven strong, broad varices per whorl with narrow interspaces. Each varix crosses the shoulder area to the preceding whorl as a thin lamella but is not joined to it. The first several varices of the teleoconch cross the lower half of the last turn of the protoconch and are attached to it. Spiral sculpture on the body whorl is of five broadly flattened, strong cords that are made up of five scabrous threads. There are two cords on each whorl of the spire. All interspaces are narrow, wider at the bottom. At the base of the aperture is one minor cord and there are two strong, flattened cords on the canal. Anterior cords are hollow at their terminations and scarcely reflected as short, stout spines at the crests of the varices. The degree of reflection increases posteriorly along the varix. The
cord at the shoulder is the heaviest and terminates as a large, reflected spine that is twisted toward the apex. There is a major, reflected, open spine at the center of the lamella on the shoulder and a much smaller one near the suture. Areas on the shoulder between the lamellae are flat and show only traces of the two cords causing the spines. The aperture is oval with a nearly complete peristome except along the parietal wall. A shallow, anal sulcus is apparent. Strong crenulations are along the erect outer lip. The spines behind the lip are roundly recurved and are joined for about half their lengths by intricate lamination. The an- terior canal is broad and moderately long, nearly straight, narrowly open to the right, and with the end distally re- curved. The top and left side of the canal each show four strong, longitudinal threads. Shell color is pinkish beige, with brown on the third spiral cord at the crests of the varices.
Type locality: Off the southern coast of Isla Santa Cruz, Galapagos Islands, Ecuador; 0°47’S Latitude, 90°21/W Longitude; four specimens dredged in 150-200 m.
Holotype: San Diego Natural History Museum, SDNHM 810610.
Dimensions of the holotype: Height 19.6 mm, maxi- mum diameter 11.4 mm.
Paratypes: Iwo paratypes are in the Carl and Laura Shy Collection, Seal Beach, California; one paratype is in the Rose Burch Collection, Seal Beach, California.
One additional specimen was brought in by a fishing boat to Guaymas, Sonora, Mexico, in 1968, probably ex- tending the range to the Gulf of California.
The specific name is taken from the Latin adjective meaning “pretty” or “charming little.”
5 INO: 1
No} N © > e o oe oO > o il a
L. H. Poorman, 1983
Page 7
Discussion: This new species is closest to Murexiella mil- dredae Poorman, 1980, in general appearance and in the low, broad, spiral cords overhanging the narrow inter- spaces (POORMAN, 1980b). It differs in having two, not three, spiral cords on each whorl of the spire, in having numerous and broadly rounded varices, in coloring, and in other sculptural details.
Murexiella venustula, spec. nov., also has a superficial resemblance to Murexiella laurae Vokes, 1970. However, the latter species has a different spine structure and has four varices per whorl (only three on some specimens) on the adult shell (POORMAN, 1980a). Also, the general col- oring of the two species is completely different.
Hollow spines formed when the leading edges com- pletely circle to touch are not unusual in Murexiella. All three of the above species are of this type. Comparison was made with a specimen of Murexiella mactanensis Emerson & D’Attilio, 1979, from Bohol Strait, Philippine Islands. Although the shells differ in general appearance, the basic spine structure is similar.
Daphnella Hinds, 1844 Type species: Pleurotoma lymneiformis Kiener, 1839-1840.
The shell is cylindro-ovate, slowly contracted to a short, open, truncated, anterior canal. The body whorl is usually more than one-half the shell height. The protoconch is reticulated and of three to four turns. The sinus is sutural, reversed L-shaped. Spiral sculpture is of fine threads over- riding numerous fine, axial ribs. There is no operculum. The shell is irregularly maculated with brown.
Daphnella levicallis Poorman, spec. nov. (Figures 3, 6)
Description: The shell is larger and more inflated than most species in the genus. The protoconch (eroded on the holotype) is of four turns, narrowly turbinate and diago- nally reticulated by fine threads, with small beads at the intersections. The first turn of the protoconch is minute and has small beads (at 250X) arranged in spiral rows and diagonal lines which, by the second turn, become di- agonal threads. The last half turn of the protoconch de- velops a slight, peripheral angulation with the reticula- tions above the angulation sagging into a band and becoming the trace of the anal sulcus on the teleoconch. The angulation becomes a cord that develops into two
l 0.5 mm
Figure 5
Protoconch of Murexiella venustula Poorman, spec. nov. X 80.
threads. These develop into the spiral cords on the teleo- conch. The protoconch terminates abruptly in a sinuosity advancing anteriorly. The teleoconch is of six rounded whorls constricted at the suture. Spiral sculpture is of strong threads throughout, 2 on the first turn and 25 on the body whorl. The trace of the anal sulcus is wide and flat, unornamented except for obscure fine threads. Axial sculpture is of numerous low rounded ribs, 10 on the first turn and 25 on the body whorl, extending to the anterior canal. Ribs are crossed by spiral threads in prominent nodes, strongest at the shoulder. The aperture is oval, with a deep J-shaped anal sulcus at the suture. The pillar is nearly straight anteriorly and has light callus. The outer lip is flaring but not produced forward, with a pronounced sinuosity at the lower part. A short, truncated, open, an- terior canal is differentiated from the aperture by an an- gulation in the lip. The outer lip is reinforced by a low ridge of callus just inside, thickest at the anal sinus and at the anterior part of the aperture. Shell color is pale brown maculated with red-brown except for an unmac- ulated band below the periphery. The third spiral cord below the shoulder is white on early whorls.
Type locality: Five km south of Tetas de Cabra, Estero San Carlos, Sonora, Mexico; 27°54’N Latitude, 111°05’W Longitude; 16 specimens dredged in 80-100 m on broken shell, small rocks, and silt bottom.
Explanation of Figures 1 to 4
Figure 1. Holotype of Murexiella venustula Poorman, spec. nov. x 5.6.
Figure 2. Holotype of Murexiella venustula Poorman, spec. noy. x 5.6.
Figure 3. Holotype of Daphnella levicallis Poorman, spec. nov. xX 6.0.
Figure 4. Holotype of Anachis (Parvanachis) mullineri Poor- man, spec. nov. X 22.
Page 8
0.5 mm l Figure 6
Protoconch of Daphnella levicallis Poorman, spec. nov. X 90.
Holotype: San Diego Natural History Museum, SDNHM 810611.
Dimensions of the holotype: Height 17.3 mm (apex eroded), maximum diameter 7.2 mm.
Paratypes: Nine paratypes are in the Forrest and Leroy Poorman Collection; two paratypes are in the Carl and Laura Shy Collection, Seal Beach, California; four para- types are in the Paul and Carol Skoglund Collection, Phoenix, Arizona; one paratype will be placed at the Academy of Natural Sciences of Philadelphia.
One additional specimen was dredged by Paul and Car- ol Skoglund in 100 m off Isla Danzante, Gulf of Califor- nia.
The specific name is a Latin noun, masculine gender, and refers to the subsutural trace of the anal sulcus as a “smooth mountain path” much like the path up the Tow- er of Babel.
Discussion: All of the recognized west American Daph- nella and the new species described here are very similar, differing only in size and details of ornamentation. The mechanism for developing the trace of the anal sulcus is observable on all. This subsutural band is also observable on the teleoconchs but is obscured except on Daphnella retusa McLean & Poorman, 1971, and the new species. Thickening of the outer lip occurs both internally and externally on the adults of all the species.
Both Daphnella retusa and Daphnella levicallis, spec. nov., occur in significant numbers off Estero San Carlos but differ in their bathymetric ranges and habitats. Daph- nella retusa is found in 30 m on gravel bottoms; whereas D. levicallis is found in 100 m on shell and silt bottoms. Daphnella levicallis is larger, heavier, and of a darker color; the axial ribs are not obsolete on the body whorl, as they are on D. retusa, but extend nearly to the anterior canal. The ribs are crossed by strong spiral cords in prom- inent nodes not occurring on D. retusa. The trace of the anal sulcus is broader and flatter on the new species, with
The Vielicers Volk ZG Nom
Figure 7
Protoconch of Anachis (Parvanachis) mullinert Poorman, spec. nov. X 30.
the axial ribs projecting slightly at their terminations to give a beaded effect to the shoulder.
Anachis (Parvanachis) Radwin, 1968 Type species: Buccinum obesum C. B. Adams, 1845.
The shell is small and obese, with a moderately high spire and flat-sided whorls with incised sutures. Body whorl and spire are of equal length. The apertural lip is thickened and denticulated. Sculpture is of prominent ax- ial ribs crossed by spiral cords.
Anachis (Parvanachis) mullineri Poorman, spec. nov. (Figures 4, 7)
Description: The shell is small and stout, consisting of a turbinate protoconch of four smooth turns and a teleo- conch of three and one-fourth whorls, terminating in a large, rounded, lip varix that decreases in size anteriorly. Transition from protoconch to teleoconch begins with weak, slanted ribs advancing anteriorly. The transition takes about one-half whorl when the ribs become longi- tudinal, rounded, and with equal interspaces. There are about 20 ribs on each whorl. The ribs are abruptly con- stricted just above the indented suture to leave widened areas in the interspaces. The ribs are rounded, protrude slightly above the shoulder, and are obsolete on the base. A spiral groove just below the indented suture cuts the ribs to produce a row of squarish beads. Below this is a region with no spiral sculpture. The middle half of the body whorl shows nine strong spiral grooves in the inter- spaces of the ribs. On the base, the spiral grooves override the diminishing ribs producing strong, flat-topped spiral cords. The entire surface of the teleoconch is covered with minute, spiral striae. The narrow aperture is somewhat trapezoidal. The outer lip is sharp, erect, and slightly crenulated by the spiral cords overriding the lip varix. Within the outer lip are six denticles. Columellar callus
L. H. Poorman, 1983
is produced into a lamella with a chink behind, both of which extend to the end of the canal (chipped on the holotype). Within the aperture, along the pillar, is a lon- gitudinal ridge of callus with six denticles. The anal sul- cus is semicircular in cross section and slightly constricted by parietal callus. The sulcus penetrates the outer lip and varix at an angle of 60° with the axis and curves to ter- minate at an angle of 90°. The short, anterior canal is at an angle of 30° left of the shell axis, scarcely differentiated from the aperture, and broadly open to the right. The shell is light horn color with a band of darker brown above the periphery and a second indefinite band on the base.
Type locality: Bahia de Santiago, Colima, Mexico; 19°02’N Latitude, 104°28’W Longitude; five specimens dredged in 20 m on sand and gravel bottom.
Holotype: San Diego Natural History Museum, SDNHM 81612.
Dimensions of the holotype: Height 5.0 mm, maximum diameter 2.8 mm.
Paratypes: Four paratypes are in the Forrest and Leroy Poorman Collection.
Additional specimens in the Paul and Carol Skoglund Collection, Phoenix, Arizona, are from: Cuastecomate, Jalisco, dredged in 25-33 m; La Cruz de Juanacaxtle, Bahia de las Banderas, Nayarit, dredged in 20 m; Playa Novellero, Nayarit, diving in 8-12 m.
The specific name is chosen in recognition of David K. Mulliner, San Diego, California, a good friend known to all for his generous contributions of time and talent to the field of malacology.
Page 9
Discussion: The massive lip varix and the unusual anal sulcus curving across it, together with the erect lamella along the pillar, are distinctive and make further compar- ison with other existing taxa unnecessary.
ACKNOWLEDGMENTS
I wish to recognize with thanks the contributions of An- thony D’Attilio, San Diego Natural History Museum, who made the protoconch drawings, and David Mulliner for technical assistance in preparing the illustrations.
LITERATURE CITED
CLENCH, W. J. & I. PEREZ FARFANTE. 1945. The genus Mu- rex in the western Atlantic. Johnsonia 1(17):1-56.
EMERSON, W. K. & A. D’ATTILIO. 1979. Six new living species of muricacean gastropods. Nautilus 93(1):1-10.
HInps, R. B. 1844{-1845]. The zoology of the voyage of H.M.S. Sulphur ... Mollusca, pt. 2, pp. 25-48 (published October 1844) London.
McLean, J. H. & L. H. PooRMAN. 1971. New species of tropical eastern Pacific Turridae. Veliger 14(1):89-113. PoorMAN, L. H. 1980a. Reinstatement of two species of Mu- rexiella (Gastropoda: Muricidae) from the tropical eastern
Pacific. Veliger 22(3):273-276.
PooRMAN, L. H. 1980b. Two new molluscan species (Gas- tropoda: Muricidae) from the tropical eastern Pacific. Ve- liger 22(4):361-363.
RapDwIn, G. E. 1968. New taxa of western Atlantic Colum- bellidae. Proc. Biol. Soc. Wash. 81:143-150.
VoKEs, E. H. 1970. The west American species of Murexziella (Gastropoda: Muricidae), including two new species. Veli- ger 12(3):325-329.
The Veliger 26(1):10-17 (July 1, 1983)
THE VELIGER © CMS, Inc., 1983
The Biology of the Northeastern Pacific Turridae. III. ‘The Habitat and Diet of Kurtziella plumbea (Hinds, 1843)
by
R. L. SHIMEK'
Friday Harbor Laboratories, Friday Harbor, Washington 98250
Abstract.
The habitat, diet, and some reproductive and mortality factors were determined for Kurt-
ziella plumbea, a shallow-water turrid gastropod from the Puget Sound region. In a shallow subtidal area with four depth-related habitats, it was found more often in upper habitats, although all of the habitats available were sandy and had similar sedimentary characteristics. In a deeper area, it was found primarily in areas of silty mud. Kurtziella plumbea is a predator of polychaetes. At the shallow site, it specialized on the oweniid Owenia fusiformis and spionids. In the deeper area, it was more generalized, but the cirratulid Tharyx multifilis was the most abundant prey item.
Egg capsule deposition occurred in the spring. There were no nurse eggs, and the time until veligers left the capsule was about 18-20 days. Settlement and metamorphosis were not observed. Growth rates of 1 to 2 mm/yr for median-sized individuals, and 3 to 4 mm/yr for small individuals were indicated.
Potential predators may include crabs and fish, but mortality factors were not conclusively deter-
mined.
INTROIDUCTION
THE MOST WIDELY distributed turrid gastropod in the shallow northeastern Pacific is Kurtzzella plumbea (Figure 1), which is found from Mazatlan (MCLEAN in KEEN, 1971) to southcentral Alaska (Shimek, unpublished data). I examined two populations of Kurtziella plumbea (here- after as Kurtzzella) to determine habitat, dietary require- ments, and aspects of predatory and reproductive behav- ior. I attempted to determine some of the reasons why this particular snail is so widespread. Two mutually contra- dictory statements about this species were examined. (1) The species is generalized in both its use of habitats and prey, and thus it can be found in many habitats. In effect, it would be a successful “Jack-of-all-trades.” (2) The species is specialized in habitat and/or diet, but the array of suitable habitats is widespread, thus permitting the snail to be widespread. Several major questions were addressed. (1) What is the relationship of diet to the potential dietary resources present? (2) Are these animals dietary or habitat
' Current mailing address: P.O. Box 6683, Bellevue, Wash- ington 98008.
specialists or generalists? (3) What is the effect of these predators upon their prey populations? (4) Are there any particular traits that limit their choices of habitats or prey?
MATERIALS anp METHODS Study Sites
All sites were subtidal, since Kurtziella is rarely inter- tidal in this region. Two major study sites were chosen: Windy Point in Dyes Inlet in lower Puget Sound and off the University of Washington Friday Harbor Laborato- ries dock on San Juan Island (Figure 2). Additional spec- imens were collected from many other localities, particu- larly in the San Juan Islands (SHIMEK, 1977); however, at these latter sites I collected only distributional data; quantitative data were seldom obtainable. Distributional information was gathered by dredge or bottom tow. All quantitative field work was done using SCUBA.
The Windy Point area, WP (47°37’25’N, 122° 40’30”W), ranges from —1.5 m to —9.0 m below MLLW. It is a topographically homogeneous, sandy subtidal re- gion unbounded laterally and divisible into four visually distinctive habitats: upper bench, upper slope, lower slope,
R. L. Shimek, 1983
Page 11
Figure 1
A. Kurtziella plumbea (Hinds, 1843). Scale in millimeters. B. Radular teeth of Kurtziella plumbea. Scale bar = 10 um. These are stabbing toxoglossan teeth used individually to pierce the prey and to introduce venom.
and lower bench, based upon the degree of slope, depth, and algal cover (SHIMEK, 1982). Kurtziella is found there with two other turrids, Ophiodermella inermis (Hinds, 1843) and Oenopota levidensis (Carpenter, 1864).
The Friday Harbor Laboratories site, FHL (48° 32/38”N, 123°00’50”W), is topographically diverse, con- taining five visually distinctive habitats: wood chips, rock, shell fragments, and shallow and deep areas of silty mud.
The site is located from —10 m to —25 m below MLLW. No discontinuities limit the site except at the upper edge where the boundary is established by the lower edge of an eelgrass, Zostera marina L., 1753, bed. No turrids were found in either the eelgrass or wood-chip areas in prelim- inary observations, consequently no quantitative sampling was done in either habitat. The remaining habitats were sampled quantitatively.
Page 12
mrAAaAbPMo
Figure 2
The Puget Sound region of Washington state showing the study sites.
Habitat Analyses
At the major sites, the physical and biological properties of the habitats were examined in detail. Sediment particle- size distributions were quantitatively determined and the remainder of the sample was washed through a 0.5-mm sieve. The animals were removed and sorted by taxon. Gastropods and polychaetes were identified to species whenever possible. Other taxa were identified to class and counted, but not detailed further (see SHIMEK, 1982, for a more complete description of sampling methods).
Sediment parameters were tabulated and statistically compared between and within the areas. Seasonal vari- ability of the sediment particle distributions was insignifi- cant, thus no seasonal comparisons were made (SHIMEK, 1982).
Polychaete assemblage abundances for each habitat were determined by the quantitative, infaunal sampling, and
The Veliger, Vol. 26, No. 1
statistical comparisons were made between and within habitats on a seasonal basis (SHIMEK, 1982).
Turrid Distribution, Collection, and Processing
Periodic transect studies from November, 1973, until December, 1975, were used to determine turrid distribu- tion, seasonal or other distributional changes, and to pro- vide a reference for the quantitative infaunal samples. ‘The significance of Kurtziella distributions compared to ran- dom habitat utilizations were calculated using log-likeli- hood ratios (G-tests) (SOKAL & ROHLF, 1969).
A hand-held, semiquantitative dredge was used at FHL to determine the relative fraction of the turrid populations buried in the sediment. Simultaneous, parallel, surface- transect surveys were conducted to compare the number of snails buried and on the surface.
Kurtziella collected from FHL and WP were individ- ually washed in sea water, isolated for up to a week, and feces were collected. The snail was then measured to the nearest 0.1 mm, and marked (SHIMEK, 1982). After mark- ing, the animal was returned to fresh sea water at ambient sea-water temperature and observed to assure no notice- able effects of measuring and marking. The animal was then transferred to a “holding” aquarium and maintained in an artificial habitat similar to the normal one. All ap- parently healthy animals were returned to their habitat, albeit seldom to the point of capture, within two weeks. Measuring and marking mortality was about five percent.
Following marking and measuring, any particulate ma- terial remaining in the collecting jar was placed on a slide, dried, mounted in polyvinyl lactophenol (A. Kohn, per- sonal communication), and examined microscopically. Identification of all fecal material was attempted. Feces consisted of mucus, radular teeth of the same animal, diatom frustules, and polychaete remains. Preliminary gut analysis by dissection indicated polychaetes swallowed whole to be the only prey. Thus only polychaete remains consisting of setae, Jaws, and occasional cuticular strips were accepted as indicators of feeding. These remains were identified by comparison with descriptions, drawings, and setal preparations of known animals, identified with stan- dard references (SHIMEK, 1982). Dietary heterogeneity was measured using H’ (KOHN & NyYBAKKEN, 1975). Turrids collected from other localities were preserved and their habitats noted, if the collecting was done with SCUBA, but no dietary analysis was attempted.
Size-frequency histograms were constructed for both populations. These were normalized to percent collected to facilitate comparison between populations because of varying sample sizes. For the purpose of determining growth rate, collections were considered quarterly: No- vember through January as Winter; February through April as Spring; May through July as Summer; and Au- gust through October as Autumn. Generally these samples were too small and/or variable for quantitative determi- nations of recruitment cohorts (BLISS, 1967); however, I
R. L. Shimek, 1983
Page 13
attempted to use seasonal shifts in histogram peaks to estimate growth rates.
Laboratory Experiments
A substrate-choice chamber was constructed, and filled to a depth of 2 cm with sediments (SHIMEK, 1982). The choices were sediments with a particle-size distribution from 0.250 to 0.500 mm, and a distribution in excess of 2.00 mm. Both sides had all detectable biota removed. Animals were placed in the chamber and one week later they were collected and their positions noted. These data were analyzed using cumulative binomial probabilities.
Egg capsules were collected from the jars in which the turrids were stored. Capsular dimensions were measured, the number of eggs per capsule was counted, and the egg diameters were measured (SHIMEK, 1982). The capsules were examined periodically. After hatching, the veligers were fed a mixture of Isochrysis sp. and Dunaliella sp.
RESULTS Habitat Descriptions
Windy Point: The four Windy Point habitats have been described in detail elsewhere (SHIMEK, 1982). Briefly, these habitats were sandy, with moderately well-sorted, uncon- solidated sediments. They were similar to each other and to the nearby sandy low intertidal areas. Algal cover in the shallower (depth < —5 m) areas varied seasonally, being very abundant in the late summer, and was mostly ulvoid algae. In the deeper areas the algal cover consisted of various red and brown algae and was less variable or dense.
Friday Harbor Laboratories: The FHL habitats are also described in SHIMEK (1982). Of the four major turrid habitats, only the rock areas could not be sampled quan- titatively for infauna and sediment. Of the three un- consolidated-sediment areas, only the lower mud was physically different, having a distinctly smaller median- sediment-particle size.
Biology of Kurtziella at Windy Point
Kurtziella was associated with the turrids Ophiodermella inermis and Oenopota levidensis at WP. All three were distributed in patches, and because of this, the mobility of these animals, asd the lack of physical boundaries to the study area, no adequate estimates of population sizes could be made. Capture and transect observational frequencies did, however, give an estimate of relative population sizes. I collected or observed 254 Ophiodermella inermis, 134 Kurtziella, and 108 O6enopota levidensis. Kurtziella and Oenopota levidensis appeared to have roughly equivalent populations. During quantitative surveys, the density of Kurtziella, when found, varied from 0.01/m? to 0.16/m?. No seasonal trends in abundances or habitats utilized were seen, but Kurtziella was found more often in the shallower
Table 1
Windy Point Kurtziella plumbea habitat utilization.
Proportion
of turrids Proportion Proportion observed — of total of turrids proportion Habitat area per area expected Upper bench 0.25 0.34 +0.09 Upper slope 0.25 0.26 +0.01 Lower slope 0.25 0.17 —0.08 Lower bench 0.25 0.24 —0.01 Number observed 134 Significance (G-test) G = 9.40 P < 0.05
areas at WP (Table 1). The sediment-particle distribu- tions were not significantly different among most of these areas (SHIMEK, 1982). Depth was probably not a factor as Kurtziella was found in the deeper areas at FHL (Ta- ble 2).
There was a patchy distribution of the polychaete fauna at WP, particularly regarding the turrid prey species Ow- enia fusiformis delle Chiaje, 1844, which was dense only in the upper bench areas, and Polydora socialis (Schmarda, 1861), which was more widely distributed than O. fuszfor- mis (Table 3). There was no seasonal pattern of predation at either site, consequently the prey-polychaete-abun- dance data were pooled. The high sample variability re- flected seasonal abundance patterns for the worms; see
Table 2
Friday Harbor Laboratories Kurtziella plumbea habitat utilization.
Propor- Proportion Propor- tion of of turrids tion of _ turrids observed —
total per proportion Habitat area area expected A. All habitats Upper mud 0.25 0.06 —0.18 Shell fragments 0.34 0.35 +0.01 Rock 0.05 0.06 +0.01 Lower mud 0.36 0.52 +0.16 Total number observed 48 Significance (G-test) P < 0.01 B. Lower habitats only Shell fragments 0.45 0.38 —0.07 Rock 0.07 0.07 0.00 Lower mud 0.48 0.56 +0.08 Number observed 45 Significance (G-test) n.s.
Page 14
A. Area: Windy Point Habitats:
Prey species
The Veliger, Vol. 26, No. 1
Table 3
Density of prey species (mean number/m? + 1 SD).
Upper bench Upper slope
Lower slope
Lower bench
Owenta fusiformis 713 + 413 IG se 37/5) ) ar DD 0 Polydora socialis 843 + 907 661 + 591 468 + 440 268 + 440 Spiophanes berkeleyorum Ole F 0 5 + 16 0 B. Area: Friday Harbor Laboratories Habitats: Upper mud Shell fragments Lower mud Prey species Myrvochele oculata 6 ae iY) 0 0 Cirratulus cirratus Sil ae 56) 23) 22 Si 7X0) ae 37 Tharyx multifilis 136 + 125 YS 22 T7/ 1B) = (35)
Spiophanes bombyx
not sampled
SHIMEK (1977, 1982) for more complete listings of the polychaetes.
Kurtziella was found to be widely, but unevenly, dis- tributed in the Puget Sound region. I dredged and/or surveyed by SCUBA 40 different sites and Kurtziella was found in only six of them (SHIMEK, 1977). All six were characterized as sandy or sandy-mud habitats.
Dietary Analysis
Dietary information obtained by fecal examination is summarized in Table 4. Kurtziella at WP ate three species of identified polychaetes. Densities of the most common prey, Owenza fusiformis, fluctuated dramatically in all but the upper-bench area, and this worm was absent from the lower-bench area completely (Table 3).
Predation on Kurtziella at WP
In the WP-slope habitats predation by crabs upon the snails may have been an important factor. Two predatory
Table 4
Results of fecal sample analysis of Kurtziella plumbea.
Area: WP FHL Total Prey species Myrtochele oculata 1 1 Owenia fusiformis 13 13 Polydora soctalis 1 1 Spiophanes berkeleyorum 2 2 S. bombyx 1 1 Cirratulus cirratus 1 1 Tharyx multifilis 3 3 Unidentified polychaetes 1 4 5 Number of snails examined 139 110 249 Percent feeding 22 9.1 10.8
H’ (identified prey only) 0.60 1.24 1.36
crabs were present, Cancer gracilis Dana, 1852, and C. productus Randall, 1839, although specimens of the latter were uncommon, probably because of too few suitable refuges (SHIMEK, 1982). During the summer when the crabs were common, Kurtziella became rare (Figure 3). Consequently, no laboratory verification of the attractive- ness of Kurtziella as a prey item was attempted. Cancer productus will eat both Oenopota levidensis and the larger Ophiodermella inermis in the same area, and Cancer gra- culis may eat small snails of all types. As Kurtziella was smaller than the other turrids at WP, it was a likely prey item for both crabs.
Biology of Kurtziella at Friday Harbor Laboratories
The turrid assemblage at FHL is diverse, in addition to Kurtziella, nine other turrids in three other genera are found there (SHIMEK, 1982, 1983). Habitat utilizations were determined from transect surveys. As with the other turrids at FHL, Kurtziella was less common in the upper- mud area than would be expected if it was randomly distributed (SHIMEK, 1982, 1983). If the upper-mud area is considered to be a boundary area that is incompletely utilized, and the data from this habitat are excluded, Kurt- ziella was collected most frequently in the lower-mud hab- itat (Table 2). When found, Kurtziella had measured abundances from 0.01/m? to 0.05/m*.
The polychaete fauna at FHL was diverse and sparse. The most abundant turrid prey, Tharyx multifilis (Moore, 1909), were present in most of the samples and habitats (Table 3). The infaunal assemblages from all of these habitats were similar in the summer, but in the winter the upper- and lower-mud areas had many differences (SHIMEK, 1982).
The substrate-preference experiments gave conclusive results, even with the small number of individuals avail- able at any one time for each test. Of the animals tested,
R. L. Shimek, 1983
Page 15
17 animals made choices; 13 chose the sediment with smaller particle-size distribution (0.250 mm-—0.500 mm), whereas only 4 chose the sediment with particles larger than 2.00 mm. The two-tailed binomial probability of a deviation this large or larger, given an equal probability of choice, is 0.049.
The hand-held, semiquantitative dredge was used in- frequently as it resulted in substantial habitat damage. Data from these dredge samples indicated equivalent numbers of Kurtziella buried and on the surface at the times of the surveys. During the surface surveys, five Kurtziella were found in 583 m?’. Simultaneous dredging parallel to, but 2 m lateral to the surface-survey-transect lines collected one Kurtziella in 116.6 m?® dredged to a depth of 0.10 m.
Dietary Analysis
Relatively few animals were found eating (Table 4), and no seasonal dietary trends were evident. At WP, Kurt- ziella was most often feeding on Owenia fusiformis, al- though spionids were also found in the diet. At FHL, no such clear-cut pattern of specialization was evident, and the snails had a more catholic diet consisting of cirratulids, spionids and oweniids. In contrast to the prey distribution at WP, the major prey taxon at FHL, the Cirratulidae, was common in all habitats (Table 3).
Kurtziella Reproduction
Collection and confinement for fecal-sample examina- tion acted as stimuli for egg-capsule deposition in some turrids (SHIMEK, 1982, 1983). Eight individuals of Kurt- ziella deposited egg capsules in captivity in March, April, and May, 1975 (Table 5). Single females deposited from one to three capsules. Capsules were smaller than the egg capsules of either Oenopota or Ophiodermella, and con- tained fewer, smaller eggs (SHIMEK, 1982, 1983). The egg capsules were deposited on the inside of the collection jar at the junction of the lateral and bottom surfaces. The eggs in 10 capsules hatched after about 18-20 days. As with Oenopota and Ophiodermella, there were no nurse eggs, and the number of veligers leaving the capsules was the same as the original number of eggs deposited. Four capsules contained eggs that did not develop at all. Pre- sumably the stimulus for oviposition was so strong that unfertilized eggs were deposited in the capsules. These capsules appeared normal in all other respects. No egg capsules of Kurtziella were seen in the field.
Life Histories
Seasonal size-frequency distributions can be examined for indications of growth rate, recruitment, and sizes of individuals in the population. A comparison of the FHL and WP populations yields some interesting observations. The WP population was composed of distinctly smaller individuals with virtually no animals exceeding 12 mm
S ce) Oo Oo S fe)
Ae) (e) ine) Cancer observed
Kurtzie//a collected
SPR SUM AUT WIN Season Figure 3
Mean (+1 SD) number of Kurtziella plumbea (open bars) col- lected and mean number of Cancer gracilis (black bars) observed (per 25 m?) by season. All habitats and seasons were pooled. Data are for Spring, 1974, through Autumn, 1975; therefore, Kurtziella was collected in only one winter.
total length (Figure 4). On the other hand, the FHL pop- ulation was composed of larger animals, with almost no animals below 10 mm total length (Figure 5). Neither population showed appreciable seasonal shifts in the size- frequency histograms, although in both populations the mean individual length increased from spring to winter, and dropped again the following spring. The pattern of changes in the mean sizes in both distributions was vir- tually identical although consistently displaced by the amount the two populations differed in mean length. Ex- amination of the seasonal shifts for both populations in-
Table 5
Kurtziella plumbea reproductive information.
Mean capsule Mean egg
SISO NB) Number/ Diameter Length Width capsule (um) 230 + 34 186 +22 180+ 43 137+8
Number examined 13 6 9
Number of capsules hatching: 10 Mean number of days in the capsule: 19.3 + 1.16 days Maximum length of survival post hatching: 27 days
Page 16
The Veliger, Vol. 26, No. 1
WINTER 1974-75 N=19
SPRING 1974 N= 43
40
Ow
2 26
oO
v
Oo
oO
S
=
2 SPRING 1975 SUMMER 1975 : 404 N=4! X&
(e}
aS QO
5 10 15 5 10 IS Length (mm) Figure 4
Windy Point seasonal size-frequency distributions. In seasons not shown (Summer, Autumn, 1974) too few snails were ob- served to make the data meaningful.
dicated a growth rate, for a 7-8 mm-long individual, of about 1.5 mm/yr. No marked animals were recaptured from the WP population. Five previously marked individ- uals were ‘recaptured from the FHL population. Three decreased in total length, and two increased. One of those two had grown 0.5 mm in 287 days, indicating a growth rate of less than 1 mm/yr. This individual was 11.9 mm long when initially captured, however; and the larger in- dividuals may grow more slowly than smaller ones, which was a pattern seen in the other turrids examined from these areas (SHIMEK, 1982, 1983).
In both populations, distinctly smaller animals were recovered only in the spring. If this species has a faster growth rate in the smaller size classes, the 4-6 mm-long individuals recovered in the spring of one year may rep- resent larvae settling the previous summer. Growth rate determinations were difficult for these animals due to their small size, the wide variation in lengths, and the lack of more than one clearly defined peak in the size-frequency histograms.
DISCUSSION
As with sympatric turrids in the genera Oenopota and Ophiodermella, Kurtziella eats tube-dwelling polychaetes;
604 SPRING 1974 N= 45
me}
&
Oo
@
©
O
S
=
oe
N WINTER 1974-75 SUMMER 1975 = N=12 N= 21 3
e 40
ss
5 © 5 ye (© 05 Length (mm)
Figure 5
Friday Harbor Laboratories seasonal size-frequency distribu- tions. In seasons not shown (Summer, 1974; Spring, 1975) too few snails were observed to make the data meaningful.
but the range of prey taken is quite broad, from oweniids to cirratulids, although at WP, Owenia predominates. The diversity of acceptable prey may be less at WP, possibly limiting animals in this population to fewer potential prey species. This might also explain the tendency of the Kurt- ziella to be found in areas where Owenia was common. Because manipulative experiments were not attempted, the turrid’s effect on its prey is uncertain, but predation by Kurtziella alone probably did not have any substantial impact on the populations of its prey. The species ap- peared to have ample food sources; indeed, Tharyx mul- tifilis, its major food, was one of the most abundant poly- chaetes in the FHL areas, and Owenia fusiformis was very abundant in some habitats at WP.
Kurtziella appears to be restricted to sandy or sandy- mud habitats and is rarely found on nearby rocky or shell- fragment habitats. Additionally, it seems to have substan- tial latitude in potential prey, although more data are needed to confirm this. The skewed distribution of Kurt- ziella at WP may indicate tracking of its most common prey species, Owenia fusiformis. Qwenia was rarely found
Rewer Shimek 1983
Page 17
below the upper-slope areas, and Kurtziella is more com- mon in these upper areas than in the lower ones.
Predatory effects on this species are difficult to deter- mine. The major predators in the WP area are inferred to be the crabs, Cancer gracilis and C. productus. Both crabs were common and have been shown to eat other, larger, turrid gastropods in the same area (SHIMEK, 1982, 1983). Nonetheless, no direct evidence of this predation was encountered. Kurtziella is a small snail with a rela- tively fragile shell, and attacks by these large crabs prob- ably result in the complete destruction of the shell. Unlike Ophiodermella and Oenopota species, Kurtziella does not show any significant tendency to bury; this may result in substantial mortality when the predatory crabs are com- mon. The relative rarity of the species at WP during and after the summer population peak of the crabs is likely the result of predation. The smaller mean length of in- dividuals in the WP population, compared to the FHL population may result from some size-selective predation by the crabs on larger snails. Immigration from deeper habitats where the crabs are less common is probably re- sponsible for the recovery of the population.
Mortality effects at FHL are unknown. During the course of study, over 100 turrid shells were recovered with hermit crabs in them: These shells proved useful in de- termining some of the causes of mortality of some of the other turrids in the region (SHIMEK, 1982, 1983), but no Kurtziella shells were recovered. This may be indirect evi- dence of predation by crushing predators like crabs, which can sometimes be found in the FHL habitat. Some fishes may also eat the snails. Except for Luidia foliolata Grube, 1866, predatory asteroids are uncommon in the area.
In both populations, the snails appear to have a defined maximum size of about 15 mm. Growth may cease or slow as the animals approach this size, thus making mea- surement of growth rates difficult. There is no indication of semilparity in this species. After spawning, the females appear healthy, and all were marked and returned to their habitat.
In conclusion, Kurtziella requires sandy or sandy-mud habitats, and overall is a dietary generalist, although it may specialize in some populations. Thus, the hypothesis that Kurtziella plumbea is a “ Jack-of-all-trades” for both diet and habitat is rejected. It is likely that suitable sandy or sandy-mud habitats are widespread on the Pacific coast of North America; this turrid should be expected in many of them. That this species will be rarely found in rocky or shell-fragment areas is also predicted.
ACKNOWLEDGMENTS
Portions of this paper are taken from a dissertation sub- mitted in partial fulfillment of the requirements for a Ph.D. in the Department of Zoology at the University of Wash- ington. Members of my graduate committee, particularly Dr. Alan Kohn, Dr. Eugene Kozloff, Dr. Paul Illg, and Dr. Ken Chew, made many helpful suggestions. The field work for this study was done with SCUBA, and while I cannot thank all 83 of my diving partners individually, Paul Raymore, Carl Nyblade, Larry Moulton, Steve Bloom, Ken Sebens, Kathy DeRiemer, and Ed DeMartini were especially helpful.
The Pacific Northwest Shell Club, Elsie Marshall and Hal Scheidt in particular, provided much information of value in locating study sites.
I thank Dr. Robert Fernald and Dr. Dennis Willows, directors, and Dr. Richard Strathmann and Dr. Eugene Kozloff, acting directors, of the University of Washington Friday Harbor Laboratories for allowing the use of facil- ities.
Earlier drafts of this manuscript were read in part or totally by A. Kohn, E. Kozloff, R. Paine, and R. Fred- rickson, and two anonymous reviewers. I thank them all for their helpful suggestions.
This work was partially supported by N.S.F. Grant 75-03303 to Dr. Kohn, by an N.S.F. doctoral dissertation grant GA-41814, by grants from the Friday Harbor Lab- oratories, and by two scholarships from the Pacific North- west Shell Club.
A final special debt is owed to R. Fredrickson, for with- out her help this work would not have been completed.
LITERATURE CITED
Buiss, C. I. 1967. Statistics in biology. Vol. 1. McGraw-Hill, New York. 558 pp.
KEEN, A. M. 1971. Seashells of tropical west America. 2nd ed. Stanford Univ. Press, Stanford, Calif. 1064 pp.
Koun A. J. & J. W. NyBAKKEN. 1975. Ecology of Conus on eastern Indian Ocean fringing reefs: diversity of species and resource utilization. Mar. Biol. 29:211-234.
SHIMEK, R. L. 1977. Resource utilization and natural history of some northeastern Pacific Turridae. Doctoral thesis, Zo- ology, University of Washington, Seattle.
SHIMEK, R. L. 1982. The biology of the northeastern Pacific Turridae. I. Ophiodermella. Malacologia 23:281-312. SHIMEK, R. L. 1983. The biology of the northeastern Pacific Turridae. II. Oenopota. J. Molluscan Stud. (in press). SOKAL, R. R. & F. J. ROHLF. 1969. Biometry. W. H. Free-
man, San Francisco. 776 pp.
Editor’s note: After the issue had gone to press, we were informed that the paper referred to as “Shimek, 1982” throughout the present article was published in 1983.
The Veliger 26(1):18-21 (July 1, 1983)
THE VELIGER © CMS, Inc., 1983
Flow Through and Around the Abalone
Haliotis kamtschatkana
by
JANICE VOLTZOW
Department of Zoology, Duke University, Durham, North Carolina 27706
Abstract.
Fluorescein dye streams released along the shell and at the shell openings of living and
dead abalones revealed the lines of water flow around and through the shell. Regardless of ambient flow speed, water entered the shell of live abalones at a region to the left of the left cephalic tentacle and also through the one or two most anterior shell openings and exited through the two or three most posterior openings. An identical flow pattern occurred through the shell of dead, intact animals when placed in an ambient flow of 6 cm/s, regardless of whether the anterior end faced upstream or down- stream. Since the exhalent openings occur at the site of the shell at which the ambient streamlines are maximally compressed, they experience a reduction in pressure relative to the anterior, inhalent ones. Thus, the design of its shell may enable the abalone to take advantage of an induced flow to move
water more efficiently through its mantle cavity.
INTRODUCTION
Hahotis kamtschatkana Jonas, 1845, the pinto abalone, must deal with changes in environmental flow while maintain- ing respiratory currents through its mantle cavity. These animals have a row of four to six openings through the dorsal shell surface that, according to earlier workers (GARSTANG, 1928; CROFTS, 1929; YONGE, 1947) evolved to prevent wastes released in the mantle cavity from mov- ing forward over the gills and head. In addition to creating a flow through its shell by beating the cilia of its gills, Haliotis could use environmental currents to help drive water through its mantle cavity. Such an induced flow requires that the inhalent openings encounter fluid at a pressure higher than that of the exhalent openings (VOGEL, 1981). MuRbDock & VOGEL (1978) found that the keyhole limpet, Diodora aspera, experiences such an externally driven flow and may use this flow to move water more efficiently through its mantle cavity. Haliotis kamtschat- kana lives in areas of surge and strong currents (Richard Emlet, personal communication), where it seems possible that its series of shell openings could be exposed to pres- sure differences sufficient for induced flow to occur. To visualize the paths that lines of water flow follow around and through abalones I combined information from dis- sections, dye streams, and flow velocity measurements tak- en in and around living and dead individuals.
MATERIALS anp METHODS
Five adult individuals of Haliotis kamtschatkana ranging in maximum aperture diameter from about 9-12 cm and collected from various sites in the Friday Harbor region of San Juan Island, Washington were used. The flow these animals normally encounter may range from 0-150 cm/s or more (Kenneth Collier, personal communication).
To relate the external flow information to the anatomy ~ of the animal, I dissected both fresh and narcotized ani- mals. To narcotize, I added increasing volumes of a 7% MgCl,-6H,0 solution to animals in cooled (8°C) sea water until the epipodial and cephalic tentacles no longer re- tracted when touched.
To visualize the flow of water qualitatively through and around Haliotis kamtschatkana, | used a stream of fluores- cein dye controlled by a micro dye injector (an adjustable syringe fitted with a drawn plastic tip and moved by a micromanipulator). Pencil marks at 1-cm intervals along the edge of the shell served as reference points for follow- ing dye paths, technically referred to as streaklines. Dye was released at each of these points along both sides of the animals as well as at various sites near the anterior and dorsal surfaces of the shells. Studies of animals in flowing and in still water took place in a 15-cm flow tank designed by VOGEL & LABARBERA (1978).
Observations of induced flow were made on animals
J. Voltzow, 1983
Page 19
Borel eRe tye
rt hata s x
ae nie Se 1
PP aa cee
Figure 1
Diagram of flow through and around an abalone facing upstream in an ambient flow of about 6 cm/s. l.c.t.: left cephalic tentacle; r.c.t.: right cephalic tentacle; m.t.: mantle tentacle; A: site at left side of shell where water enters mantle cavity; 1, 2: anterior, inhalent shell openings; 3, 4, 5: posterior, exhalent shell openings; dot-dash lines (—----): inhalent streaklines; dashed lines (— — —): exhalent streaklines; dotted lines (----- ): flow along anterior end and side of shell. Letters and numbers at ends of exhalent streaklines correspond to the points at which streaklines
may have entered the mantle cavity.
that were first relaxed in MgCl, as above and then quickly frozen to —20°C by placing them in the bottom of a cryo- stat. The animals were returned to ambient sea water temperature before any data were taken.
RESULTS
Dye released at specific points around an animal facing upstream in an ambient flow of about 6 cm/s formed a repeatable set of streaklines (Figure 1). Water approach- ing the anterior edge of the shell was either deflected up- ward (perpendicular to the general direction of flow), straight upstream (180° to the general flow), or was passed in a series of vortices along either side of the shell. Flow contacting the shell at either side continued downstream close along the shell and then became caught in the tur- bulent backwash behind the animal. In ambient flows ranging from approximately 2-15 cm/s the streaklines
did not appear to be velocity-sensitive, although there was more turbulence at higher speeds.
Abalones accepted incoming water only at specific sites along the shell (Figure 1: A, 1, 2). At the lower edge of the shell, water entered in a region 1~3 cm to the left of the left cephalic tentacle. It appeared that the animals could control the entrance at this region by waving the left cephalic tentacle. Dye released in the region between the two cephalic tentacles sometimes traveled along the edge of the shell, over the left tentacle and eye, and into the mantle cavity. At other times under the same flow conditions it was deflected by the tentacles and passed downstream alongside the shell.
The two most anterior openings of the shell also served as sites of water intake. Depending upon the position of the mantle tentacles, dye released upstream, above, or be- side these openings entered the mantle cavity. If the an- terior opening was incomplete, resembling a fold at the
Page 20
The Veliger, Vol. 26, No. 1
edge of the shell, dye released just below its dorsal edge proceeded into the mantle cavity, while dye released at other points within the same region traveled up and out away from the shell, as mentioned above.
Only the two or three most posterior openings on the top of the shell served as the animals’ exhalent passages from the mantle cavity. In all cases the penultimate open- ing (4 in Figure 1), which ordinarily has no mantle ten- tacle, was the chief channel for wastes and exhalent water flow. The most posterior opening was often partially sealed and always had a tentacle, both of which reduced its out- put volume and rate. The center-most opening, which usually had a mantle tentacle, tended to be weakly inhal- ent, although at times dye streams also exited from it. Dye streams usually exited from the posterior or from the right side of the exhalent openings and were laminar.
Except at regions of exhalent and inhalent currents, dye released at the sides of animals standing in still water did not move. The inhalent and exhalent regions were at the same locations in animals in still water as they were in moving water.
Dye released at the inhalent openings of dead, intact abalones facing upstream in a flow of about 10 cm/s en- tered the mantle cavity at the site of release and exited through one of the exhalent openings. Shells of the same animals oriented downstream had similar patterns of flow through them, although the rate of the induced flow was not as high. In either orientation, dye released near ex- halent openings did not enter the shell, but continued downstream.
DISCUSSION
Although earlier reports indicated that water enters the abalone mantle cavity only under the margin of the shell and mantle flap on either side of the head (STEPHENSON, 1924; CRrorTs, 1929; YONGE, 1947), it is well known now that in at least some species the first hole serves for water intake as well (e.g., ABBOTT & HADERLIE, 1980, p. 233). In Haliotis kamtschatkana the streaklines show that flow enters the mantle cavity in a restricted region to the left of the head and through the first, and sometimes second, shell opening. Only the posterior openings are exhalent, and they are the only channels by which water and ex- cretory products may exit the mantle cavity.
The fact that the shell of a dead animal shows’ flow patterns through its openings similar to those of a live animal suggests that by its design, the animal may take advantage of an induced flow. Because of the shell shape, the exhalent openings lie in the region at which the streamlines over the shell are maximally compressed, leading to a reduction of pressure over the posterior open- ings relative to the anterior ones, which should cause the fluid to enter at the front and to exit at the rear (VOGEL, 1981). Location of openings relative to any wake formed and the geometry of the openings may also determine local pressure, but these aspects of flow were not investigated.
The orientation of the openings may further enhance the induced flow. As openings form at the anterior edge of the shell, they face the oncoming flow when the animal is facing upstream, and thus encounter dynamic pressure, or the pressure created due to stopping fluid (VOGEL, 1981). As the shell grows and new openings are added, older openings rotate relative to a horizontal surface, be- coming more nearly parallel to flow, so that by the time they reach the central region of the shell and begin to function as exhalent openings they experience the reduced pressure described above. Thus as an animal grows, each opening performs first an inhalent and later an exhalent function. I noticed that on each animal there is one open- ing (or sometimes two) that may be both slightly inhalent near its anterior edge and exhalent near its posterior edge. Such transitional openings are located on the cusp of the shell and are oriented at an angle intermediate to openings that are strongly inhalent or exhalent. It may be that there is some angle at which an opening may no longer serve as an entrance to, and another at which it may begin to serve as an exit from, the mantle cavity. It is also possible that the cephalic and mantle tentacles may valve the open- ings and help control the direction and rate of flow.
Since induced flow may occur whether animals are fac- ing upstream or downstream, they may need only be par- allel to the general direction of surge to take advantage of it. This would make induced flow useful in regions of surge where flow reversal is common. It would be valuable to know if abalones orient to flow in their natural habitat and to what degree orientation is necessary for utilizing induced flow.
Traditionally, workers have believed that the openings in an abalone’s shell evolved primarily as a way to avoid mixing fresh inhalent water with waste-laden exhalent water. I have shown that in addition to eliminating this problem, the shell determines the path by which water will enter, as well as exit, the mantle cavity. Whether or not this design increases the efficiency of moving water through the mantle cavity will require a study of the en- ergetics of water movement.
ACKNOWLEDGMENTS
This work began as a project for a course in biomechanics taught by Dr. Steven Vogel and Dr. Michael LaBarbera at the University of Washington’s Friday Harbor Labo- ratories. I thank them for their generous supply of equip- ment and encouragement. I also wish to thank the Pacific Northwest Shell Club and Dr. Stephen Wainwright for their support, and Vogel, Wainwright, and Dr. H. Fred- erik Nijhout for commenting on the manuscript.
LITERATURE CITED
AppotTtT, D. P. & E. C. HADERLIE. 1980. Prosobranchia: ma- rine snails. Jn: R. H. Morris, D. P. Abbott & E. C. Had- erlie (eds.), Intertidal invertebrates of California. Stanford Univ. Press, Stanford, Calif. pp. 230-307.
J. Voltzow, 1983
Crorts, D.R. 1929. Haliotis. Liverpool Mar. Biol. Com. Mem. 29:1-174.
GarsTaNnG, W. 1928. The origin and evolution of larval forms. Brit. Assoc. Adv. Sci. Report of the 96th Meeting: pp. 77- 98.
Murpock, G. R. & S. VOGEL. 1978. Hydrodynamic induction of water flow through a keyhole limpet (Gastropoda, Fis- surellidae). Comp. Biochem. Physiol. 61A:227-231.
STEPHENSON, T. A. 1924. Notes on Haliotis tuberculata. J. Mar. Biol. Assoc. U.K. 13:480-495.
Page 21
VoGEL, S. 1981. Life in moving fluids: the physical biology of flow. Willard Grant Press, Boston, Mass. 352 pp.
VoGEL, S. & M. LABARBERA. 1978. Simple flow tanks for research and teaching. BioScience 28:638-643.
YONGE, C.M. 1947. Pallial organs in aspidobranch gastropods and their evolution throughout the Mollusca. Phil. Trans. R. Soc. Lond. B 232:443-518.
The Veliger 26(1):22-25 (July 1, 1983)
THE VELIGER © CMS, Inc., 1983
Shell Strength in Corbicula sp.
(Bivalvia: Corbiculidae) from the
Potomac River, Maryland
VICTOR S. KENNEDY
Horn Point Environmental Laboratories, University of Maryland, Cambridge, Maryland 21613
JAY A. BLUNDON
Department of Zoology, University of Maryland, College Park, Maryland 20742
Abstract. Forces required to crack intact shells of the freshwater Asiatic clam, Corbicula sp., were determined. They are higher than those which crack the wedge clam, Rangia cuneata, a globose, strong- shelled, oligohaline bivalve. Asiatic clam shell shape and strength may explain published data on crayfish predation on this animal in Oklahoma and Tennessee, in which predation was successful only on clams less than 6 mm in size or those with holes in the shell. Strong shells may also help prevent damage during periods of high river flow or strong water movement.
INTRODUCTION
CLAMS OF THE ASIATIC genus Corbicula were apparently introduced to western North America early in this cen- tury, becoming widespread in the ensuing years (BRITTON & Morton, 1979; CounTs, 1981). Recently, laboratory experiments by CovicH ef al. (1981) revealed that two species of freshwater crayfish were able to feed only on specimens of Corbicula that were less than 6 mm in size or that had damaged (perforated) shells. The Asiatic clam is globose in shape and the shell is relatively thick, giving the impression of strength. MACKIE (1978) noted that the thickness of the shell of Corbicula fluminea was greater than the shells of 22 other species of sphaeriacean bivalves he investigated.
In an earlier study of crustacean predation on estuarine bivalves, we examined shell strength of eight species of clams (BLUNDON & KENNEDY, 1982). Here we present measurements of shell strength of the Asiatic clam, com- pare them with the strength of the estuarine bivalves, and relate the results to the findings of CovicH et al. (1981) concerning crayfish predation on Corbicula.
TAXONOMY oF EXPERIMENTAL ANIMALS
There has been much confusion associated with the tax- onomy of Corbicula in North America, with BRITTON & Mor Ton (1979) having declared the species to be Corbic- ula fluminea. However, HILLIS & PATTON (1982) have presented evidence that two species of Corbicula (a “white form” and a “purple form’) are present in the Brazos River, Texas. The specimens we tested in this report re- sembled the “white form” in color of nacre. Our speci- mens were collected from the Potomac River at Whites Ferry, Maryland (approximately 39°09’N; 77°31’W) in shallow water close to the river bank, a habitat in which HILuis & PATTON (1982) found the “white form” to pre- dominate. However, the mean number of growth rings (“annuli”) for our sample was less than for the Texas sample and, when number of annuli was plotted against shell mass for each clam, all our values fell below the “envelope” surrounding the values that HILLIs & PATTON (1982) derived (their Figure 1) for the “white form” in Texas.
V.S. Kennedy & J. A. Blundon, 1983 Page 23
400
300
200 o Cc . ro) Corbicula sp. eel logY=1.96 log X-0.30 c uJ 2 86 3 log Y= 2.31 Le
Rangia cuneata log Y= 2.42 log X -1.73 —~> 10 | 5 10 20 30 40 50 LENGTH (mm) Figure 1 Predictive regression ( ) and geometric mean functional regressions (----- ) for shell strength of Asiatic clam
(Corbicula sp.) and wedge clam (Rangia cuneata) from Maryland. Wedge clam data are from BLUNDON & KENNEDY
(1982).
We agree with HILLIs & PATTON (1982) that the as- signment of a species name to populations of Corbicula is unwarranted until conclusive taxonomic studies are per- formed; thus we have called our bivalves Corbicula sp. in this report. In referring to the reported work of others, we have kept the species names they used. Specimens from our study population have been deposited with the Smith- sonian Institution’s National Museum of Natural History (USNM 804414).
METHODS
To test for shell strength, we used an Instron testing ma- chine, an industrial instrument that measures compression applied to a surface (BLUNDON & KENNEDY, 1982). Clams were crushed with a steel bar, 11 mm in diameter, which moved vertically downward at a velocity of 4 mm/s. Clams were crushed in the umbo region, parallel to the dorso- ventral axis. A chart recorder was used to record force (in
newtons) required to crack the clam shell. A 10-newton weight was used to calibrate the Instron before and during the experiment. Clams for crushing were collected from Whites Ferry and were crushed immediately upon return to the laboratory (within 2 h of collection).
RESULTS
Initially, log,, force (Y) was regressed on log,, length (X), length being the maximum anterior—posterior axis in mm, and a regression line (log Y = 1.96 log X — 0.30) was fitted (Figure 1). The coefficient of determination, R?, was equal to 0.73 (n = 70). Because the measurements of force and size are subject to error of measurement, a geometric mean estimate of the functional regression may be a more appropriate linear regression (RICKER, 1973). The resul- tant equation (Figure 1) is: log Y = 2.31 log X — 0.76. This curve is significantly different from zero (P < 0.001).
As a comparison with these data, the geometric mean
Page 24
regression for Rangia cuneata, an oligohaline bivalve res- ident in Chesapeake Bay, is presented in Figure 1. Rangia cuneata, like the Asiatic clam, is a globose bivalve with a thick shell and closely fitting valves. It was the strongest bivalve we tested in our survey of shell strength of eight estuarine bivalves (BLUNDON & KENNEDY, 1982). How- ever, the Asiatic clam had a stronger shell than did R. cuneata (Figure 1). The slopes of the geometric mean regression for the two species were not significantly dif- ferent (P > 0.05), according to the test statistic of CLARKE (1980). However, the elevations of the two curves were significantly different (P < 0.001), as determined by Ho- telling’s T? (MorRISON, 1967).
DISCUSSION
As noted earlier, MACKIE (1978) found that the shell of Corbicula fluminea was the thickest of the shells of 23 species of sphaeriacean clams he studied. Neither MACKIE (1978) nor CoUNTs & PREZANT (1982) present evidence that the shell of Corbicula fluminea is unusual in its struc- tural material or in the arrangement of that material. In addition to shell thickness, the globose shape of the Asiatic clam, like Rangia cuneata, is probably an important reason for the crushing resistance being so high.
CovicH et al. (1981) noted that freshwater crayfish, Procambarus clarkiu, attacked the edge of the shell of Asiat- ic clams with their mandibles. Repeated chipping of the shell led to eventual penetration. Such chipping away at shell edges should allow a relatively weak predator to open a strong-shelled bivalve. This chipping method was successful only with clams less than 6 mm long. Asiatic clams greater than 6 mm were successfully preyed upon by the crayfish Cambarus bartoni if the clams had suffered damage, such as perforations in the shell, which allowed the crayfish to reach their first walking leg into the soft clam body.
BROWN et al. (1979) found that a 33.7-g specimen of Procambarus clarku could exert an average force of 9.9 newtons in the region of the base of the chelipeds, with force decreasing to 3.4 newtons near the tip of the che- lipeds. The P. clarkit used by Covicu et al. (1981) ranged in size from 21.0-34.6 g, averaging 27.8 g. Using our geometric mean regression equation, we find that a 4-mm and 6-mm long Asiatic clam (respectively, the minimum and maximum size of undamaged prey that P. clarki opened, according to COVICH et al., 1981) have an average shell strength of about 4 newtons (4-mm clam) to 11 new- tons (6-mm clam). Thus, if our data are transferable to southern clams, the crayfish used by CovIcH et al. (1981) may not have been able to crush the Asiatic clams greater than 6 mm long, even if they had used their chelipeds in a crushing attempt (Covich et al. do not report any at- tempts by P. clarki to use their chelae to crush shells).
The Veliger; VoljZoyiNowm
Theoretically, the larger crayfish (e.g., 34.6 g) could crush the smallest (4 mm) clams available, assuming that the chelae could grip the globose shell appropriately.
With regard to other sources of shell damage that might leave Asiatic clams susceptible to crayfish predation, our clams were collected from a substrate of gravel and peb- bles covered with silt, with cobble stones and boulders also present. Fast river flow during floods (e.g., in spring) might cause substrate movement, with tumbling of clams or rocks and with grinding and pressure on shells. Strong shell structure would seem a useful protective measure under such conditions. CovicH et al. (1981) found damaged (perforated) shells in a rocky region of variable water flow below a dam. We have not noted much broken or damaged shell in our monthly surveys of Asiatic clams in our col- lecting area; most dead shell has consisted of intact valves.
We conclude that the thickness and globose shape of the shell of the Asiatic clam, which probably accounts for its considerable strength, should provide protection from predator crushing attack, especially for larger clams. This strength may also protect the clams in situations where they, or rocks, are being tumbled about in fast-flowing waters.
ACKNOWLEDGMENTS
Partial support for this research was provided by Power Plant Siting Program Contract P87-82-04 from the Maryland Department of Natural Resources. We ac- knowledge the assistance of Laurie Van Heukelem. Deb- orah Kennedy drew Figure 1. Contribution No. 1378HPEL of the Center for Environmental and Estua- rine Studies.
LITERATURE CITED
BLUNDON, J. A. & V. S. KENNEDY. 1982. Mechanical and behavioral aspects of blue crab (Callinectes sapidus Rathbun) predation on Chesapeake Bay bivalves. J. Exp. Mar. Biol. Ecol. 65:47-65.
BRITTON, J. C. & B. Morton. 1979. Corbicula in North America: the evidence reviewed and evaluated. Jn: J. C. Britton (ed.), Proceedings, First International Corbicula Symposium. pp. 249-287.
Brown, S. C., S. R. Cassuto & R. W. Loos. 1979. Biome- chanics of chelipeds in some decapod crustaceans. J. Zool. (Lond.) 188:143-159.
CLARKE, M. R. B. 1980. The reduced major axis of a bivariate sample. Biometrika 67:441-446.
Counts, C. L. 1981. Corbicula fluminea (Miiller) on the Del- marva Peninsula. Veliger 24:187-188.
Counts, C. L. & R. S. PREZANT. 1982. Shell microstructure of Corbicula fluminea (Bivalvia:Corbiculidae). Nautilus 96: 25-30.
Covicu, A. P., L. L. DyE & J. S. Mattice. 1981. Crayfish predation on Corbicula under laboratory conditions. Am. Mid]. Nat. 105:181-188.
Hiuis, D. M. & J. C. Patron. 1982. Morphological and electrophoretic evidence for two species of Corbicula (Bival-
V.S. Kennedy & J. A. Blundon, 1983 Page 25
via: Corbiculidae) in North America. Am. Midl. Nat. 108: Morrison, D. F. 1967. Multivariate statistical methods. 75-80. McGraw-Hill, New York. 338 pp. Mackig, G. L. 1978. Shell structure in freshwater Sphaerea- Ricker, W. E. 1973. Linear regressions in fishery research.
cea (Bivalvia:Heterodonta). Can. J. Zool. 56:1-6. J. Fish. Res. Board Can. 30:409-434.
The Veliger 26(1):26-29 (July 1, 1983)
THE VELIGER © CMS, Inc., 1983
Relationship Between Beak Morphometrics and Live Wet Weight of the Giant Pacific Octopus, Octopus dofleint martini (Wiilker)
by
SHAWN M. C. ROBINSON anp E. BRIAN HARTWICK
Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6
Abstract.
Twelve separate beak measurements were taken on 73 different sets of beaks and a
relationship was established with the live weight of Octopus doflein: martin: (Wiilker). The pigment upper-lateral-wall length best predicted the weight of the octopus after taking the natural logarithm of each measurement. Pigment lengths were found to be slightly more accurate than the corresponding total lengths. We could find no set of measurements which would permit discrimination between sexes
based on beak morphometrics.
INTRODUCTION
THE HORNY MANDIBLES, called beaks, found within the buccal mass of cephalopods have received attention for a number of different reasons. There has been considerable interest in their function during feeding (ALTMAN & Nixon, 1970), the organization of their movements (BOYLE et al., 1979a, b) and their potential in taxonomic work (CLARKE, 1962a, b; AKIMUSHKIN, 1965; MANGOLD & FIORONI, 1966; CLARKE & MacLEop, 1980; IVERSON & PINKAS, 1971). Studies also indicate the possibility of us- ing beak measurements to estimate cephalopod body size (CLARKE, 1962b; Nixon, 1969, 1973) and in the case of the squid Illex illecebrosus to differentiate between sexes (MERCER ef al., 1980).
The ability to identify cephalopods by their beaks and to estimate their size from measurements of these hard parts provides considerable opportunity to extract infor- mation from stomach analyses of marine predators. Such information includes indications of predator migratory patterns (CLARKE & STEVENS, 1974), predator diet (see, for example, PITCHER, 1981; RANDALL et al., 1981), ceph- alopod distribution (CLARKE, 1962c), and the relative im- portance of cephalopods in the ecology of the oceans (CLARKE, 1977). Clarke’s report of 18,000 beaks in the stomach of one sperm whale gives some impression of their importance to these marine mammals.
Much of the work on beaks has centered on various species of squids, although NIxon (1969, 1973) has car-
ried out studies on Octopus vulgaris beaks. No information is available on beaks of the giant Pacific octopus, Octopus dofleini, although a brief description is given by WINKLER & ASHLEY (1954) and PICKFORD (1964). Pickford de- scribes possible growth lines on beaks and records rostral length indices for this species.
Octopus dofleint martin: is an abundant, fast-growing form inhabiting the coastal waters of British Columbia and extending as far south as California. Its current sta- tus, as a candidate for fisheries development (HARTWICK et al., 1978), means that information on its distribution, mortality and predator-prey size relationships is desirable. Since examination of beaks may provide such information, an attempt was made to measure a series of beak dimen- sions and to relate these to body size and sex.
MATERIALS anp METHODS
During May, 1981, to February, 1982, 73 animals (15 males, 58 females) were captured in Clayoquot Sound on the west coast of Vancouver Island, British Columbia. SCUBA was used to collect the octopuses, and the first animals encountered were captured and taken to a vessel at the surface. After draining the mantle cavities, live wet weights were taken using spring scales sensitive to 0.25 kg for animals over 3 kg and 0.025 kg for animals less than 3 kg. The entire buccal mass was then removed from the animal and stored in 10% formalin in seawater. Later, beaks were gently excised from the surrounding muscle
S. M. C. Robinson & E. B. Hartwick, 1983
Page 27
UPPER BEAK
1-UHL 2-PUCL 3-TUCL 4-PULWL 5- URW
LOWER BEAK
6-LHL 7-PLWL 8-TLWL 9-TSLWL 10-PLCL 11-TLCL 12-LRW
Figure 1
Measurements taken on upper and lower beaks of Octopus do-
fleini.
tissues and measured, using Vernier calipers, to the near- est 0.05 mm. Twelve measurements per beak were taken using terminology modified from CLARKE (1962b). As the octopus grows, new chitin is added to the edge of the wings, crest, and lateral wall (NIxon, 1969). This leaves a translucent margin on the edges where it has not become dark and horny. The interface of this translucent area with the pigment is used for the measurement of the pig- ment length. The measurements taken were: pigment up- per-crest length (PUCL), pigment lower-crest length (PLCL), pigment upper-lateral-wall length (PULWL), pigment lower-wing length (PLWL), total upper-crest length (TUCL), total lower-crest length (TLCL), total lower-wing length (TLWL), total standard-lower-wing length (TSLWL), upper hood length (UHL), lower hood length (LHL), upper rostral width (URW), and lower rostral width (LRW) (Figure 1).
Analysis of the data was carried out using least-squares regression and discriminant analysis, both statistical com- puter package programs (MIDAS). Correlation tests were taken from SOKAL & ROHLF (1969, p. 521).
RESULTS anp DISCUSSION
In this study, we attempted to predict the live wet weight of the octopus from the beak measurements. This was chosen over other measurements, such as the dorsal man- tle length, since body weight seems to be a more accurate measurement of size than length in live material (NIXON, 1968). The weight range of animals measured was from
Table 1
Regression statistics of the natural logarithm of beak mea-
surements (mm) versus the natural logarithm of live wet
weight (kg) for Octopus dofleini (n = 73). (r = correlation
coefhicient; SE = standard error of regression; m = slope; b = y-intercept.)
Measurement Toa SE m 19)
In PULWL 0.970 0.044 0.274 2.674 In PLWL 0.967 0.045 0.265 2.969 In PUCL 0.965 0.048 0.277 B22 In PLCL 0.959 0.050 0.268 DO In TLWL 0.946 0.053 0.245 3.074 In TSLWL 0.938 0.058 0.248 2.926 In TUCL 0.934 0.060 0.247 BATS In TLCL 0.927 0.068 0.264 2.832 In UHL 0.921 0.061 0.228 2.382 In LHL 0.909 0.074 0.253 1.954 In URW 0.885 0.082 0.244 1.216
In LRW 0.784 E13) 0.261 1.059
* All r’s are highly significant at the 99% confidence level.
0.95 to 22.75 kg with a mean weight of 7.64 kg. There was a non-linear increasing function of beak measure- ments on wet weight so the natural logarithms of both axes were taken in order to obtain a linear function. A transformation to the cube root of the live wet weight was also attempted, to test whether a better fit of the data to a line was obtained, but the fit was not as good as taking the natural logarithm of both axes.
The relationships between the twelve measurements on the upper and lower beaks may be seen in Table 1. It is apparent from this table that all the beak measurements are good predictors of octopus weight with the correlation coefficients (r) ranging from 0.784 to 0.970. Although the best measurement is the pigment upper-lateral-wall length (PULWL), shown in Figure 2, there is really very little difference among the first three measurements. All of the beak measurements in Table 1 have been grouped from the highest correlation coefficient to the lowest and this resulting hierarchy allows one to choose the best mea- surement that is available. A hierarchy of possible mea-
Table 2
Significance of the correlation coefficient values between corresponding pigment and total length beak measure- ments (Fisher’s z transformation).
Comparison 1 vs. 2 n z(1) z(2) IP <<
In PUCL In TUCL if 2.0191 1.6902 0.052 In PLCL In TLCL 73 1.9345 1.6376 0.080 In PLWL In TLWL 73 2.0484 1.7943 0.133
Page 28 3.6 An A A 3.45 Ae
3.2- A
In Pigment Upper Lateral Wall Length (mm)
2.87 OA A 205 = Th Rae sa = 0 1 2 3 4
In Octopus Weight (Kg) Figure 2
The relationship between pigment upper-lateral-wall length and live wet weight of Octopus dofleini (natural logarithms of both axes).
surements would be advantageous if only one of the beaks was available and/or it was damaged in some way neces- sitating an alternate measurement.
Our results compare favorably with those of NIXON (1973) with Octopus vulgaris. She found that after boiling the beaks in a 5% potassium hydroxide solution to remove the surrounding muscle tissue, there was a high degree of correlation (r = 0.97 with n = 77) between the logarithm of live wet weight and the logarithm of crest length of the upper beak. It is interesting to note that the correlation coefficient for the pigment upper-crest length (PUCL) in our study is essentially the same as Nixon’s with approx- imately the same number of samples taken, and that an upper-beak measurement is generally more accurate in predicting weight than its corresponding one on the lower beak.
In our study, essentially two types of measurements were made: pigment lengths and total lengths, although four measurements—UHL, LHL, URW, and LRW— were not readily assignable to either of these. As can be seen from Table 1, there is a distinct grouping of mea- surements with the pigment lengths in every case having higher correlation coefficients than the total lengths. To
The Veliger, Vol. 26, No. 1
determine whether a significant difference existed between these two types of measurements, Fisher’s z-transforma- tion test was carried out (Table 2). Three sets of corre- sponding measurements were used, and the data show that there is only a slightly significant difference between them (ranging from P < 0.05 to P < 0.13). Despite the low levels of significance, the use of pigment lengths over total lengths is warranted by the fact that often the delicate translucent edge will be destroyed if the beak is not care- fully removed from the muscle tissue of the buccal mass.
Although MERCER et al. (1980) were able to differen- tiate between sexes of the squid Illex illecebrosus using beak morphometrics in a discriminant analysis, our at- tempts to find a set of beak measurements in Octopus dofleint which would separate sexes using this technique were unsuccessful. Although this may have been due, in part, to a small sample size of males, there was a large degree of overlap between the generated male and female discriminant values.
ACKNOWLEDGMENTS
This work was supported by a National Sciences and Engineering Research Council grant and a Canada Fish- eries and Oceans grant to E. B. Hartwick. We gratefully acknowledge the help of D. Trotter, L. Tulloch, M. Walsh, and G. Cox for their valuable assistance in the field and to R. Lockhart for his advice with the analysis.
LITERATURE CITED
AKIMUSHKIN, I. I. 1965. Cephalopods of the seas of the USSR. Translation of 1963 Russian edition by A. Mercado, Je- rusalem. 223 pp.
ALTMAN, J. S. & M. Nixon. 1970. Use of beaks and radula by Octopus vulgaris in feeding. J. Zool. (Lond.) 161:25-38.
BoyLeE, P. R., K. MANGOLD & D. FROESCH. 1979a. The man- dibular movements of Octopus vulgaris. J. Zool. (Lond.) 188: 53-67.
Boy.e, P. R., K. MANGOLD & D. FROESCH. 1979b. The or- ganization of beak movements in Octopus. Malacologia 18: 423-430.
CLARKE, M. R. 1962a. Significance of cephalopod beaks. Na- ture 193:560-561.
CLARKE, M.R. 1962b. The identification of cephalopod “beaks” and the relationship between beak size and total body weight. Bull. Br. Mus. (Nat. Hist.) 8:419-480.
CLARKE, M. R. 1962c. The identification of cephalopod beaks and their significance in systematic and ecological studies of squids and their predators. Rep. Challenger Soc. 3(14):43- 44.
CiarkE, M. R. 1977. Beaks, nets and numbers. Symp. Zool. Soc. Lond. 38:89-126.
CriarkE, M. R. & N. MacLeop. 1980. Cephalopod remains from sperm whales caught off western Canada. Mar. Biol. 59(4):241.
CLARKE, M. R. & J. D. STEVENS. 1974. Cephalopods, blue sharks and migration. J. Mar. Biol. Assoc. U.K. 54:949- 957.
Hartwick, E. B., P. A. BREEN & L. TULLOCH. 1978. A re- moval experiment with Octopus dofleini (Wiilker). J. Fish. Res. Board Can. 35(11):1492-1495.
S. M. C. Robinson & E. B. Hartwick, 1983
Page 29
Iverson, I. L. K. & L. Pinkas. 1971. A pictorial guide to beaks of certain eastern Pacific cephalopods. Calif. Dep. Fish. Game, Fish Bull. 152:83-105.
MANGOLD, K. & P. FIORONI. 1966. Morphologie et biométrie des mandibules de quelques céphalopodes Méditerranéens. Vie et Milieu 17:1139-1196.
Mercer, M. C., R. K. Misra & G. V. Hurvey. 1980. Sex determination of the ommastrephid squid Illex ilecebrosus using beak morphometrics. Can. J. Fish. Aquat. Sci. 37: 283-286.
Nixon, M. 1968. Growth of radula in Octopus vulgaris. J. Physiol. (Lond.) 196:28P-30P.
Nixon, M. 1969. Growth of the beak and radula of Octopus vulgaris. J. Zool. (Lond.) 159:363-379.
Nixon, M. 1973. Beak and radula growth in Octopus vulgaris. J. Zool. (Lond.) 170:451-462.
PICKFORD, G. E. 1964. Octopus dofleini (Wiilker). Bull. Bing- ham Oceanogr. Coll. 19(1):1-70.
PircHer, K. W. 1981. Prey of the Steller sea lion, Eumetopias jubatus, in the Gulf of Alaska. U.S. Nat. Mar. Fish. Serv. Fish. Bull. 79(3):467-472.
RANDALL, R. M., B. M. RANDALL & E. W. KLINGELHOEFFER. 1981. Species diversity and size ranges of cephalopods in the diet of jackass penguins from Algoa Bay, South Africa. S. Afr. J. Zool. 16(3):163-166.
SOKAL, R. R. & F. J. ROHLF. 1969. Biometry. W. H. Free- man, San Francisco. 776 pp.
WINKLER, L. R. & L. H. ASHLEY. 1954. The anatomy of the common octopus of northern Washington. Walla Walla Coll. Publ. Biol. Sci. Number 10 (November 10, 1954).
The Veliger 26(1):30-36 (July 1, 1983)
THE VELIGER © CMS, Inc., 1983
Studies on the Reproductive Biology of Some
Prosobranchs from the Coast of Pakistan Bordering
the Northern Arabian Sea. II]. Egg Capsules and
Larvae of Four Species of Thais
SOHAIL BARKATI anp MUZAMMIL AHMED
Institute of Marine Biology, University of Karachi, Karachi-32, Pakistan
Abstract. Egg masses of four species of Thais, namely, 7. rudolphi, T. carinifera, T. bufo, and T. tissoti, are reported from the coast of Pakistan for the first time. Based on the incidence of their egg capsules, the respective breeding seasons of the four species are: June to September, February to November, April to August, and March to August. The four species deposit benthic egg capsules from which free-swimming veligers are hatched. A comparative account of numbers and dimensions of capsules, number and sizes of eggs, and developmental periods of shelled larvae is presented.
INTRODUCTION
THE EGG MASSES and capsules of prosobranch mollusks, apart from the fact that they are of scientific interest in themselves, yield information about the breeding seasons of the parent species, may prove of assistance in the precise identification of closely related species, and provide larval stages and juveniles should there be a need for their com- mercial rearing. Although the literature in this field is vast, only the following are the major publications on the gastropods of the Arabian Sea: (THORSON (1940) from the Persian Gulf; NATARAJAN (1957) from the Gulf of Ma- nnar and Palk Bay; GOHAR & EISAWAY (1962, 1967a, b) from the Red Sea; and DEsal (1962), GANAPATI & SASTRY (1973), RAMAMOORTHY & NATARAJAN (1973), and Ka- SINATHAN et al. (1974) from different parts of the Indian coast. No information is available on the egg masses and larval development of marine gastropods from the coast of Pakistan bordering the northern Arabian Sea. It was in view of this paucity of information that a project was initiated in 1976 at the Institute of Marine Biology, Uni- versity of Karachi, to study the same. Observations on the juveniles of the gastropod Planaxis sulcatus from the coast of Karachi have already been published (BARKATI & AHMED, 1982). The present report on four species of Thazs is the second in the series.
MATERIAL anp METHODS
In order to collect egg masses and capsules of local gas- tropods, regular biweekly visits were made during the period June, 1976, to July, 1977, to Buleji, which is a rocky and partly sandy-cum-muddy beach about 18 km northwest of Karachi. Egg capsules were also collected rather irregularly from some other beaches in the Karachi area, namely, Manora Island, Keamari Seawall, Paradise Point, and Korangi Creek, and from Gawader and Jiwani on the Mekran coast, about 600 km northwest of Karachi. Some egg capsules had been collected prior to June, 1976, and others after July, 1977. Except for a couple of rainy months in summer the salinity at all these sites is high, ranging from 36-40%. In most of the cases the spawning female snails were present near their egg masses. It was difficult to ascertain the number of egg capsules spawned by individual snails since the capsules are laid together. During the study, therefore, only representative samples of egg capsules were collected although some of these con- sisted of the entire lots of capsules spawned by individual snails.
Attempts to spawn specimens of the different species of Thais in the laboratory in limited quantities of water did not succeed. The egg capsules, and the larvae hatching from these, were maintained in filtered and aerated sea
S. Barkati & M. Ahmed, 1983
Page 31
water in 1600-ml glass bowls. They were fixed in 5% formalin and then preserved in 70% ethanol for subse- quent study. Measurements of the size of capsules, eggs, and larvae were made with an ocular micrometer on a microscope. Illustrations were prepared with a camera lucida.
OBSERVATIONS Breeding Season
The four species of Thais investigated occur near the low and mid-tidal zones of the rocky beaches of the coast of Pakistan. The number of egg masses of four species collected from different localities is given in Table 1. It is apparent from this table that 7. rudolphi (Lamarck) spawns from June to September, 7. tissot: (Petit) from March to August, and 7. bufo (Lamarck) from April to August. An egg mass of 7. carinifera (Lamarck) was taken at station 45 (63°46/N latitude) along the Mekran coast on March 1, 1977, in a purse seine haul of the Norwegian Fisheries Research Vessel “Dr. Fridtjof Nansen” (egg capsules of this species in THORSON’s [1940] collection from the Persian Gulf were obtained from a depth of 11- 22 m). Since some of the capsules in this egg mass were of purple color they must have been spawned in February. Recently, an egg mass of 7. carinifera was also collected from Port Qasim, about 30 km southeast of Karachi. The spawning season of 7. carinifera on the coast of Pakistan, therefore, seems to extend from February to November.
Characteristics of Egg Capsules, Eggs, and Larvae
Egg capsules of 7. rudolphi (Figure 1A, B), like those of other species of Thais, are creamy white in color when deposited and become dark gray with the advancement of embryonic development. A change in color from yellow to gray was also observed by NATARAJAN (1957) in 7. bufo. The capsules are deposited in clusters of several irregular, short rows imparting a circular shape to the egg mass in general. There is always one layer of capsules the basal plates of which unite to form a common basal membrane that is firmly glued to the substratum. Each capsule has translucent, tough leathery walls. An aperture for the re- lease of larvae, 0.32 mm in diameter, is present slightly off center on the flattened, apical surface of each capsule and is covered with a transparent membrane which rup- tures at the time of larval hatching. Dimensions of cap- sules, eggs, and larvae of this species are given in Table 2. The larvae just after hatching (Figure 1C, D) possessed shell lengths of 211 to 251 um and widths of 171 to 182 um. They swam actively and gathered near the walls of the glass bowls. Their shells consisted of one and a half whorls. They measured 353 to 376 wm in height and 274 to 285 wm in width 36 h after hatching.
The egg mass of 7. carinifera consists of closely spaced, stalkless, somewhat curved and thin tubular capsules that
Table 1
The incidence of egg masses of four species of Thais on the coast of Pakistan. Exposure of shore abbreviated as: Exposed, E; Protected, P; Semi-exposed, SE; Subtidal,
ST. Expo- Egg Locality sure Date Year masses T. rudolphi Manora Island E June 9 1970 Many Buleji E June 15 1976 1 Manora Island E June 16 1976 2 Buleji IE; July 2 1976 2 Buleji E July 3 1977 4 Buleji E August 13 1976 1 Paradise Point E August 26 1975 1 Buleji E September 8 1975 1 Buleji E September 9 1976 2 Paradise Point E September 9 1976 1 T. carinifera Mekran Coast ST March 1 1977 1 Jiwani SE April 29 1979 g Korangi Creek P April 30 1978 1 Native Jetty le May 1972 Many Buleji E June 14 1980 1 Keamari Seawall 1? August 1 1976 3 Port Qasim P November 1 1982 1 T. tissot Sandspit Bridge P March 16 1979 1 Jiwani SE April 29 1979 2 Korangi Creek P April 30 1978 1 Buleji SE June 4 1980 1 Manora Island E June 9 1970 Many Keamari Seawall rR August 1 1976 1 Korangi Creek 12 August 21 1977 Many T. bufo
Jiwani SE April 29 1979 1 Keamari Seawall P May 1975 3 Keamari Seawall P May 18 1976 1 Manora Island E June 9 1970 Many Keamari Seawall P June 13 1975 1 Manora Island E June 13 1979 1 Keamari Seawall P August 1 1976 1
have very smooth translucent walls without any ridges (Figure 2A, B). They are of uniform width but taper at the apex to form a nipple-like structure. The apex func- tions as an operculum which is shed at the time of hatch- ing so as to provide an exit for the larvae. This aperture is 0.4 mm in diameter. Dimensions of capsules, eggs, and larvae of this species are given in Table 2. The larvae 12 h after hatching (Figure 2C, D) measured 388 X 295 um. Their shell walls were smooth and transparent and con- sisted of one and a half whorls. They attained a size of 401 X 301 wm (Figure 2E) after 36 h of development. Very few larvae survived in the laboratory for 60 h with- out food. The egg mass of 7. carinifera was described
Page 32
The Veliger, Vol. 26, No. 1
Figure 1
Thais rudolphi: A. dorsolateral view of a portion of an egg mass; B. dorsolateral view of an egg capsule; C. ventral view of a larval shell just after hatching; D. dorsal view of the same; E. ventral view of 36-h larval shell.
earlier by ANNANDALE & Kemp (1916) from Chilka Lake, India, and by THORSON (1940) from the Red Sea. Na- TARAJAN (1957) also described an egg mass that closely fits the above description but he was not able to assign it to any species.
Egg capsules of 7. tissot: are stalkless (Figure 3A, B) and attach themselves to the substratum by their basal plates, which unite to form a basal membrane. The cap- sules are smaller than those of 7. carinifera. They are cylindrical, somewhat broader in the middle, taper at both ends, and curve on one side. Their walls are smooth and without ridges. A preformed aperture for the release of larvae does not exist but the apex of the capsule sheds off at the time of hatching. The part shed measures 0:72 X 0.32 mm across. Dimensions of capsules, eggs, and larvae of this species are given in Table 2. The larval shell (Fig- ure 3C) soon after hatching consists of one and a half whorls. Changes in the size of the larval shell of this species with time are shown in Table 3. The larvae thrived in the laboratory without food for about nine days but showed very little increase in shell dimensions after 84 h. The maximum shell dimensions recorded were: height 467 pm and width 456 um.
The capsules of 7. bufo (Figure 4A, B, C) have smooth and very thick walls, are tubular in shape, and have long thin stalks which unite at the base and are glued to the substratum. The proximal end of the capsules is swollen
and carries a rounded aperture for the exit of larvae. The aperture measures 0.49 to 0.58 mm in diameter and is covered by a thin membrane. The larvae (Figure 4D, E) hatch from the capsules as free-swimming veligers. Their dimensions appear in Table 2.
The egg mass of 7. bufo was earlier described from south Indian waters by Gravely (1942, in NATARAJAN, 1957), Chari (1950, in NATARAJAN, 1957) and by Na- TARAJAN (1957) and the above account describes it closely.
An egg mass was collected from the bottom of a crevice of a steep rocky ledge at Paradise Point that might be from a fifth species of Thais (or another muricid). This ball-like egg mass measured 2.4 X 2.2 cm across and con- sisted of two layers of low rounded and irregularly shaped capsules which were stalkless, with their basal plates united to form a common membrane.
DISCUSSION
Observations made during the present study show that three of the four species of 7hais examined, namely, 7. bufo, T. tassoti, and T. carinifera, spawn for about six to seven months in the spring and summer during the period February to August, whereas 7. rudolphi has the shortest spawning season of four months, restricted to the summer months of June to September. There is evidence that spawning in at least two of these species, namely, 7. bufo
S. Barkati & M. Ahmed, 1983
Page 33
Figure 2
Thais carinifera: A. dorsolateral view of a portion of an egg mass; B. lateral view of a single egg capsule; C. ventral view of veliger shell 12 h after hatching; D. dorsal view of the same; E. ventral view of larval shell 36 h after
hatching; F. front view of the same.
Table 2
A comparative account of the characteristics of egg capsules, eggs, and larvae of four species of Thavs.
as averages with the range of values given in parentheses.
Data are presented
Characteristics T. rudolphi T. carinifera T. tissoti T. bufo Approximate size of females (cm) 6.8 4.6 32 5.8 (4.0-8.0) (3.5-6.0) (2.5-4.0) (4.0-7.0) Number of egg capsules per mass 170 247 257 80 (97-257) (220-268) (255-295) (65-92) Capsule height (mm) 4.6 91 4.2 7.9 (3.8-5.0) (8.0-10.5) (4.0-4.4) (7.2-9.0) Capsule width (mm) 533 13) 1.2 2.0 (4.0-6.1) (1.2-1.5) (1.1-1.2) (1.8-2.5) Number of eggs per capsule 1094 140 37 228 (813-1422) (120-160) (25-40) (183-268) Egg diameter (um) 142 230 215 252 (137-148) (216-250) (200-250) (198-350) Hatching time (days) UF 19 19 20 (16-18) (18-20) (18-20) (18-22) 8220x255
Larval size at hatching (Lx W) (um) 224 x 173 340 X 276 231 x 198
Page 34
The Veliger, Vol. 26, No. 1
Figure 3
Thats tissott: A. dorsolateral view of a portion of an egg mass; B. lateral view of a single egg capsule; C. ventral view of veliger shell taken out of a capsule; D. ventral view of 24-h veliger shell; E. front view of 84-h veliger
shell; F. front view of larval shell 13 days after hatching.
and 7. carinifera, may commence slightly earlier on the coast of Mekran than on the coast of Karachi. Be as it may, spawning in the four species of 7hazs seems to occur with the rising temperatures of spring and summer when a lowering of salinity may also occur due to the southwest monsoon rains (see AHMED, 1980).
The study shows that 7. rudolphi produces the highest
Table 3
Changes in the size of the larval shell of Thais tissott. Egg size 1s 200-225 um.
Size (um) Just after hatch- ing 12h 36h 60h 84h 9d Length 231 281 313 338 385 460 Width 198 229 232 269 302 442
numbers of eggs per capsule, and 7. carinifera, T. bufo, and 7. tissote follow it in that order. Survival of the brood in the natural environment seems to be in the same pro- portion, since 7. rudolphi is the most abundant species of Thais on the coast of Karachi followed by 7. carinifera. Thais rudolphi has not been recorded from Gawader and Jiwani on the Mekran coast where 7. carinifera does occur (AHMED et al., in press). Thais rudolphi, the species with the highest fecundity, also has been found in the present study to have eggs and larvae of the smallest size among the four species. Larvae of the four species spend about 16-22 days within egg capsules but those of 7. rudolphi hatch the earliest.
Species of Thais are known to display two types of larval development. The first is the indirect development in which pelagic planktotrophic or lecithotrophic veliger larvae hatch from egg capsules. The second is direct or non-pelagic development in which crawling miniature snails emerge from egg capsules and where a planktonic stage is missing. The four species of 7hais examined in the present study also possess indirect development, which
S. Barkati & M. Ahmed, 1983
Page 35
Figure 4
Thais bufo: A. lateral view of an egg mass; B. and C. dorsal and ventral views of egg capsules; D. ventral view of a veliger shell taken out of a capsule just before hatching; E. front view of the same; F. tip of an egg capsule.
is shown by a majority of the species of Thais studied so far in different parts of the world: for instance, 7. cari- nifera (THORSON, 1940); 7. fasciata (LEBOUR, 1945); 7. coronata (KNUDSEN, 1950); 7. bufo, T. tissotz, and three unidentified species of Thais from India (NATARAJAN, 1957); and 7. haemastoma (D’AsaArRo, 1970). Species that show direct development are 7. hippocastaneum (THORSON, 1940), 7. lapillus (see THORSON, 1940), 7. lamellosa, T. emarginata (=T. lima), and T. canaliculata (see AHMED & SPARKS, 1970), and 7. emarginata (LEBOEUF, 1972; SPIGHT, 1976). There are, however, instances where members of the same species of 7hais may behave differently under different environmental conditions. For instance, 7. hae- mastoma is believed to have pelagic larval development in Louisiana but direct development in the West Indies (see THORSON, 1950; NATARAJAN, 1957). Lyons & SPIGHT (1973) have considered the members of the Muricacea as sufficiently variable that geographically separated species may develop according to the local conditions. We wish to point out here that some workers feel that the above reference to direct development in the West Indian species of Thais is based on misinformation and should not be attributed to either Thorson or Natarajan.
It is generally believed that species of prosobranch mol- lusks occurring in cold waters of higher latitudes show direct development but those occurring in warm tropical and subtropical latitudes possess pelagic indirect devel- opment (THORSON, 1950). However, MILEIKOvSKyY (1971) pointed out, as an exception to Thorson’s generalization, that pelagic development is not altogether absent in colder waters of higher latitudes and that an occasional species may display such a developmental pattern. Also as an exception can be mentioned the case of the gastropod Planaxis sulcatus which shows direct development on the coast of Karachi, a subtropical locality (BARKATI & AHMED, 1982).
LITERATURE CITED
AHMED, M. 1980. The breeding and recruitment of marine animals of the coast of Pakistan bordering the Arabian Sea. Proc. First Pakistan Cong. Zool: pp. 55-96.
AHMED, M., H. N. Rizvi & M. MoazzaM. The distribution and abundance of intertidal organisms on some beaches of Mekran coast in Pakistan (northern Arabian Sea). Pakistan J. Zool. (in press).
AHMED, M. & A. K. Sparks. 1970. A note on the chromosome
Page 36
number and interrelationships in the marine gastropod ge- nus Thais of the United States Pacific coast. Veliger 12:293- 294.
ANNANDALE, N. & S. Kemp. 1916. Fauna of the Chilka Lake. Mollusca, Gastropoda and Lamellibranchiata with an ac- count of the anatomy of the common Solen etc. Mem. Ind. Mus. Calcutta: pp. 328-366.
BARKATI, S. & M. AHMED. 1982. Studies on the reproductive biology of some prosobranchs from the coast of Karachi (Pakistan) bordering the northern Arabian Sea. I. Obser- vations on Planaxis sulcatus (Born, 1780). Veliger 24(4): 355-358.
D’Asaro, C. N. 1970. Egg capsules of prosobranch mollusks from South Florida and the Bahamas with notes on spawn- ing in the laboratory. Bull. Mar. Sci. 20:414-440.
Desal, B. N. 1962. A preliminary note on the eggs and larvae of some marine molluscs of Bombay. Curr. Sci. (Bangalore) 4:158-159.
GanapaTl, P. N. & S. R. Sastry. 1973. The spawn of a cymatid gastropod, Cymatium pileare. Curr. Sci. (Bangalore) 42(1):25.
Gonar, H. A. F. & A. M. Elsaway. 1962. The egg masses and development of Trochus erythraeus from the Red Sea. Publ. Mar. Biol. Sta. Al-Ghardaqa, Egypt, No. 12:191- 203.
Gonar, H. A. F. & A. M. Etsaway. 1967a. The egg masses and development of four taenioglossan prosobranchs from the Red Sea. Publ. Mar. Biol. Sta. Al-Ghardaqa, Egypt, No. 14:109-147.
Gouar, H. A. F. & A. M. ElsAway. 1967b. The egg masses and development of five rachiglossan prosobranchs. Publ. Mar. Biol. Sta. Al-Ghardaqa, Egypt, No. 14:215-268.
The Veliger, Vol. 26, No. 1
KASINATHAN, R., K. GOVINDAN & R. NATARAJAN. 1974. Notes on spawning and hatching of three species of Gastropoda. Malacol. Rev. 7:133-135.
KNUDSEN, J. 1950. Egg capsules and development of some marine prosobranchs from tropical west Africa. Atl. Rep. 1: 85-130.
LEBOEUF, R. 1972. Thais emarginata: description of the veliger and egg capsule. Veliger 14(2):205-211.
Lrespour, M. V. 1945. The eggs and larvae of some proso- branchs from Bermuda. Proc. Zool. Soc. Lond. 114:462- 489.
MILEIKovsky, S. A. 1971. Types of larval development in marine bottom invertebrates, their distribution and ecolog- ical significance: a re-evaluation. Mar. Biol. 10(3):193-213.
Lyons, A. & T. M. SpicHT. 1973. Diversity of feeding mech- anisms among embryos of Pacific Northwest Thais. Veliger 16:189-194.
NATARAJAN, A. V. 1957. Studies on the egg masses and larval development of some prosobranchs from the Gulf of Man- nar and the Palk Bay. Proc. Ind. Acad. Sci., Sect. B. 46: 170-228.
RAMAMOORTHY, K. & R. NATARAJAN. 1973. Spawning in Te- lescopium telescoprum. Venus 31(4):157-159.
SpiGHT, T. 1976. Hatching size and the distribution of nurse eggs among prosobranch embryos. Biol. Bull. 150:491-499.
THORSON, G. 1940. Studies on the egg masses and larval de- velopment of Gastropoda from the Iranian Gulf. Danish Scientific Investigations in Iran, Part IJ:159-238. Ejner Munkegaard, Copenhagen.
TuHorson, G. 1950. Reproductive and larval ecology of marine bottom invertebrates. Biol. Rev. 25:1-45.
The Veliger 26(1):37-46 (July 1, 1983)
THE VELIGER © CMS, Inc., 1983
Comparison of Northern and Southern Populations
of Epitonium tinctum (Carpenter, 1864)
Onethe California Coast
CAREY RESCH SMITH
Santa Barbara Museum of Natural History, 2559 Puesta Del Sol Road, Santa Barbara, California 93105
AMY BREYER
Department of Biology, Sonoma State University, Rohnert Park, California 94928
Abstract. Epitonium tinctum (Carpenter, 1864) was collected for several years from Bodega Head to the north and from Carpinteria Beach to the south of Point Conception, California. Northern populations contained longer shells than southern populations. Northern snails became sexually mature and changed sex at a larger size than southern snails. There were no distinguishable differences in the weight and width of specimens between northern and southern snails of similar length. Variation in shell shape (squat versus elongate) between populations did not exceed variation within each population. Shell length and the number of body whorls overlapped substantially between the two sites. The size and abundance of snails collected monthly fluctuated more throughout the year in the northern popu-
lation than in the southern population.
INTRODUCTION
ALONG THE WEST coast of North America the wentletrap Epitonium (=Nitidiscala) tinctum is found intertidally in association with the aggregate or clonal anemone Antho- pleura elegantissima (Brandt, 1835). Epitonium tinctum ranges from Magdalena Bay, Baja California to Forrester Island, Alaska (DUSHANE, 1979). As protandric her- maphrodites, the snails mature first as malesyjthen, at a larger size they change sex and function as females (BULNHEIM, 1968; BREYER, 1982). Females produce a number of sand-encrusted egg cases which are strung to- gether with a strong elastic mucous thread attached to the substrate or to the shell. When exposed at low tide, snails bury themselves in the sand between anemones and are often aggregated around a cluster of egg cases. When sub- merged during high-tide periods the snails become active and feed on the expanded tentacles of the anemones (HocHBERG, 1971; SMITH, 1977; BREYER, 1982). In order to feed, the snails evert an acrembolic proboscis and either
slip the distal end over a tentacle tip or attach it at some point along the length of the tentacle. Jaws and radula are used to sever a portion of the tentacle which is then ingested upon retraction of the proboscis (RESCH, 1972).
The shell of Epztonium tinctum can grow to over 10 mm in length. It has three nuclear whorls and up to 8 post- nuclear whorls with about 12 thin axial costae continuous from whorl to whorl. STRONG (1941) examined shells from north and south of Point Conception, California, and not- ed that northern specimens were longer and appeared to be heavier and broader than southern individuals. He sug- gested the subspecific name of swbcoronatum for the north- ern form. Although DUSHANE (1979) described similar differences, she did not recognize the subspecies suwbcoro- natum because radulae from northern and southern snails were indistinguishable.
Individuals of populations living in food-rich environ- ments or in warm climates may be expected to grow faster than those living in more severe environments. This faster
Page 38 128° 126° 124° 122° —- DN 42° * Bodega Head / / ( 40° San 1 Francisco \ St 38° Point ‘ Conception \ SC
Carpinteria Beach—
Los \ e Angeles
36°
34°
7 A
Figure 1
Map of California showing two study sites located north (Bodega Head) and south (Carpinteria Beach) of Point Conception.
growth may lead to an altered size at maturity and per- haps an important difference in generation time. In the present work we document differences within and be- tween populations of Epitonium tinctum to the north (Bo- dega Head) and to the south (Carpinteria Beach) of Point Conception, California (Figure 1). Providing the major basis for comparison are shell parameters, which include: length, width, weight, and number of whorls and costae. Distinct population modes were computed from measure- ments of shell length. The mean minimum size at. onset of sexual maturity and sex change were calculated from lengths of juveniles, males, and females. Additionally, fluctuations in size and abundance were noted monthly from July, 1977, to July, 1979, for populations at Bodega Head, and from July, 1978, to June, 1980, for popula- tions at Carpinteria Beach.
MATERIALS ann METHODS Collection Sites
The northern collecting site was in Horseshoe Cove located on the exposed outer coast of Bodega Head, So-
The Veliger, Vol) Zo3Noml
25]
BE Bodega Head (n= 1692)
[) Carpinteria Beach (n=840)
no (eo) —
= = fo) a ——_ —
Percent of Total Number of Snails Collected o 4
1 2 3 4 5 6 7 8 9 ie) 4 Size Class (mm shell length)
Figure 2
Comparison of E. tinctum shell length and the percentage of total number of snails collected from 1977 to 1980.
noma County, California. In a protected area on the northern side of the cove, a 3-m-wide surge channel lo- cated about 10 m from shore is bordered on one side by a cliff. The channel is parallel to the cliff for about 15 m until its mouth opens toward the west. Wave disturbance in this channel is reduced, not only because waves break to the south, but also because it is protected by an exten- sive rock shelf. At this site clones of Anthopleura elegan- tissima cover extensive areas on the sides and bottom of the channel. In the summer and fall, when wave action is reduced, the sand between the anemones is fine grained and at least 10 mm deep. During the winter, when wave action is heaviest, the amount of fine sand between the anemones is reduced, disappears altogether, or is replaced by coarser sand. Snails were collected from the anemone beds on both sides of the channel.
The rocky reef area at Carpinteria Beach State Park, Santa Barbara County, California was the southern col- lecting site. Carpinteria Beach, like much of the southern California coastline south of Point Conception, is char- acterized by sandy beaches interrupted by intermittent rocky outcrops or headlands. The Carpinteria Beach site consists of a sandy beach extending out from the cliff about 100 m to where the first rock outcrop begins. In the mid-intertidal region of the rocky reef both clonal and solitary Anthopleura elegantissima are present. Epitonium tinctum is most often found in protected areas on these rocks in sand which accumulates within pockets between clonal anemones and beneath the algal cover of Ulva lobata (Kutzing, 1849) and Gigartina canaliculata (Harvey, 1841).
C. R. Smith & A. Breyer, 1983
Page 39
Bodega Head
Number of Individuals
2 3 4 5 Shell Length (mm)
7 8 9 10 11 12
[] Juvenile Ao As [9
Carpinteria Beach
i 8 9 10 11 12
Figure 3
Comparison of £. tinctum shell length versus the number of juveniles, males, and females in each population. Snails in transition from male to female (possessing both spermatozeugmata and ova) are also indicated.
Although this area receives gentle surf year around, a perceptible change occurs in the structure of the beach between summer and winter. In summer, a sand bar fills in the area between the shore and the first rock outcrop. Sand, several centimeters in depth, fills in the crevices between clonal anemones and covers many of the solitary anemones, which are primarily located lower in the in- tertidal. Algae flourish during this time and cover exten- sive surfaces of rocks. During winter storms much of the sand cover is removed from between the clonal anemones and the algal cover on the rocks is reduced.
Methods
Epitonium tinctum was collected approximately month- ly at low tide from each site; from July, 1977, to June, 1979, at Bodega Head and from July, 1978, to June, 1980, at Carpinteria Beach. Additional collections were made in 1980 and 1981 at both locations. Snails were collected by carefully searching among aggregations of
Anthopleura elegantissima in an area approximately 3 m? for 30 minutes. Similar areas, exposed at mean lower low water, were used for repeated collections at each site. Snails were located by visually scanning the area or by lightly stroking the anemones with fingertips. Pressure on the anemone body caused the release of a small amount of fluid which washed over the anemone bed and removed some sand and debris. When the tip of a snail or a clump of eggs was spotted it was carefully removed by hand. Often a mucoid thread was attached from the snail or eggs being removed to other snails and eggs in an aggregation. Care was taken to remove all snails and eggs in a partic- ular aggregation before searching for additional snails. Lengths and widths of snails were measured using a variety of dissecting microscopes with calibrated ocular micrometers. The number of post-nuclear whorls was de- termined by placing the shell with the operculum facing upward and counting from the largest body whorl to the smooth nuclear whorls. Axial costae were counted from the first costa behind the outer lip, around the body whorl,
994
504
Percent Sexually Mature Individuals
e Bodega Head
x Carpinteria Beach
0.01
1 2 3 4 5 6 7 8 9 10
Size Class (mm shell length)
Figure 4
Mean minimum size of E. tinctum at onset of sexual maturity. A. Males replaced juvenile snails at an average length of 2.6 mm in Bodega Head and 1.9 mm in Carpinteria Beach. B. Females replaced males at an average shell length of 7.3 mm in Bodega Head and 5.4 mm in Carpinteria Beach. No significance test was run between sets of lines; an appropriate test is not yet in print (Wenner, in preparation).
to the point where the first costa met the costa directly above it. Weights (to 0.1 mg) were obtained on a Mettler balance from animals and shells originally preserved in 50% isopropyl alcohol, which were removed from the al- cohol and allowed to air dry 24 hours at room temperature before weighing. ;
To determine sex, snails preserved in 70% ETOH or 50% isopropyl alcohol were first measured and then placed in a vial filled with Bouin’s solution for 24 hours to dis- solve their shells. Individuals were then examined with a dissecting microscope at approximately 50. Males were recognized by the presence of spermatozeugmata, which were clearly visible as very white, almost iridescent strands densely packed in the gonad especially to the right of the stomach. Females were distinguished by the absence of spermatozeugmata and the presence of oocytes and ova. Several snails, termed hermaphroditic, were characterized
The Veliger, Vol. 26, No. 1
by having proximally located spermatozeugmata and dis- tally located oocytes and ova in their gonads.
Probability Paper Analysis of Polymodal Frequency Distributions
The technique of plotting cumulative normal distribu- tions on probability graph paper, first descrbed by Har- DING (1949), with methodology presented by CAssIE (1950), is a valuable graphical method with which to ana- lyze bimodal or polymodal size-frequency distributions in a population. In a polymodal size-frequency sample, in- dividual modes may be expanded and the mean and stan- dard deviation calculated from each mode (see CASSIE, 1954, for method). If modes are compared from two or more populations, subtle differences may be distinguished. Probability paper analysis has been utilized to compare sex ratios and size in crustacean populations (WENNER, 1972) and to define and compare the mean minimum size at onset of sexual maturity in populations of the sand crab Emerita analoga (Stimpson, 1857) from different locations (WENNER et al., 1974).
RESULTS
A compilation of size-frequency data for all snails col- lected and measured over a two-year period in Bodega Head and Carpinteria Beach is presented in a histogram (Figure 2). From these data a polymodal analysis of each population was calculated by the use of probability graph paper. That analysis indicated larger snails were more prevalent at the northern site than at the southern site. The modes that appear in each population were then ex- panded, also by the use of probability paper. Three dis- tinct modes were calculated for each population consisting of small, medium, and large snails. For Bodega Head these values were, respectively, as follows: x = 2.20 + 0.55 mm, n= 152; x = 5.40 + 1.20 mm, n= 1134; x= 8.35 + 1.15 mm, n = 406. For Carpinteria Beach values were, respectively: x = 2.65 + 0.77 mm, n=193; x= 4.75 + 0.90 mm, n = 487; x = 7.20 + 0.90 mm, n = 160. Since these snails are protandric hermaphrodites, chang- ing from juveniles to males and then from males to females as they grow, the modes that appear possibly represent the juveniles, males, and females in each population. More than 600 snails were examined for the presence or absence of spermatozeugmata during spring and fall (Figure 3). The size at which these protandric hermaph- rodites became sexually mature and changed sex was greater in the northern population than in the southern population. In the transition from male to female in each population, snails were occasionally found with both sper- matozeugmata and ova present. The data for transition of juveniles to males and males to females were plotted on probability paper (Figure 4) and the mean minimum size was calculated (e.g., WENNER et al., 1974). The mean size of females was larger at Bodega Head (7.3 mm) than at
C. R. Smith & A. Breyer, 1983
Page 41
Dh
NO [o) ———e
= oa fi
= ——
Log Snail Weight (mg)
e Bodega Head
x Carpinteria Beach
T aa fo T
1 2 3 4 5
Vier aa ree T
6 7 8 9 10 11
Snail Length (mm)
Figure 5
Comparison of E. tinctum length versus weight. A complete overlap existed between sets of points, so only one
curve was fitted (by inspection).
Carpinteria Beach (5.4 mm). The mean size of juveniles was also larger at Bodega Head (2.6 mm) than at Car- pinteria Beach (1.9 mm).
The weights of snails (from 1.7 to 91.3 mg) in each population were obtained for snails ranging in length from 1.9 to 11.0 mm (Figure 5). The results revealed little variation in weight of snails at the same length between populations. The width of snails relative to shell length from both populations varied somewhat (Figure 6). We observed that some snails within each population ap- peared to have either a more squat or more elongate shell shape than the others. Although the range of variation within each population was notable, regression lines did not differ significantly between northern and southern populations. Snails of similar lengths varied considerably in number of body whorls (Figure 7), but did not differ appreciably between populations. The number of axial costae on the largest body whorl of shells from both lo- cations ranged between 11 and 14, which agreed with DUSHANE’s (1979) findings.
The size and abundance (Figure 8) of Epitonium tinc- tum collected monthly at Bodega Head fluctuated more than in similar collections from Carpinteria Beach. Small snails (less than 3 mm) were found occasionally through- out the year at Bodega Head; however, they were most common from late winter to early summer. In 1978 many small snails were found in March and April; in 1979 few small snails were found until June; in 1980 many small snails were found in January. Every year during the sum- mer and early fall, snails were common. In 1978 the mean shell length increased every month during this period. In the fall large females (longer than 8 mm) were most com- mon, and particularly large clusters of egg cases associated with large aggregations of snails were found (Figure 9A). In the late fall and early winter the abundance of snails declined. Snail abundance decreased from December, 1977, to February, 1978, and from February to May, 1979. Snails remained rare until an influx of small snails ap- peared.
No clear annual pattern was shown at Carpinteria
Page 42
ithe Vieligern) Vols Zo Noms
5.5
5.0
4.5
4.0
Shell Width (mm)
KS) a
2.0
e Bodega Head x Carpinteria Beach
a a enn ne 7
T T T
a 1 2 3 4 5
6 7 8 9 10 11
Shell Length (mm)
Figure 6
Comparison of E. tinctum length versus width. The slopes of the lines were not significantly different (P > 0.01). The regression for Bodega Head was y = 0.22 + 0.43x (n = 95) and Carpinteria Beach was y = 0.33 + 0.39x (n=
94).
Beach for size or abundance of snails collected from July, 1978, to June, 1980. The mean snail length (4.5 to 6.0 mm) remained fairly constant through time. Newly settled snails (less than 3 mm in length) occurred commonly at all seasons. The largest individuals were observed sporad- ically throughout the year. Egg masses were recorded in the field in all collections in equal abundance. Snails with eggs most commonly occurred as individuals or in small groups (2-4 individuals) with few egg capsules per egg mass (less than 50 to about 500). Larger snail groups (10- 15 individuals) and large egg masses (1000-5000 eggs) occurred without respect to season (Figure 9B). During the winter of 1981, severe storms washed away large amounts of sand from Carpinteria beaches. It was difficult to cross on foot from the cliff to the first rock outcrop, because of the diminished sand coupled with large waves. In February, 1981, the population of snails was greatly reduced. An influx of small snails (mean length 3.5 mm)
was noticed in the spring (April, 1981). A population fluctuation occurred at Carpinteria Beach that year sim- ilar to fluctuations observed at the Bodega Head site.
DISCUSSION
Our results support the literature on physiological varia- tion in intertidal molluscs summarized by NEWELL (1964). He concluded that northern species generally attain a larger final size than southern ones. WEYMOUTH et al. (1931) studied the razor clam Stliqua patula (Dixon, 1789), and concluded that growth in southern localities was ini- tially more rapid, but less sustained and hence led to smaller total lengths. There are several reasons why snails may grow larger at higher latitudes. Higher latitudes gen- erally imply a decrease in temperature coupled with an increase in environmental stresses. CHOW (1975) conclud- ed that the largest Littorina scutulata (Gould, 1849) had
C. R. Smith & A. Breyer, 1983
Page 43
5
Number of Individuals
5
Number of Post-Nuclear Whorls >
| Bodega Head
O Carpinteria Beach
1 2 3 4 5
7 8 9 10 11
Shell Length (mm)
Figure 7
Comparison of E. tinctum shell length and number of post-nuclear whorls. Along each line the numbers of
individuals are arranged by collecting locality.
higher tolerances to desiccation, wave shock, and osmotic stress. Thus, a larger snail may be equipped to survive the harsher environment of higher latitudes better than a smaller snail.
Recently Breyer (personal observation) observed that southern California Epitonium tinctum, collected from Santa Barbara and raised in the laboratory at the Uni- versity of California, Santa Barbara, are capable of grow- ing as large as northern California snails. At present we do not know why snails in the field in southern California do not grow as large as those collected in northern Cali- fornia.
Latitudinal variations in populations of Epitonium tinc- tum closely resemble those found by FRANK (1975) for the black turban, Tegula funebralis (A. Adams, 1855). In ad- dition to finding larger snails in northern latitudes, Frank found that individuals in northern 7egula populations ma- ture at a larger size and have irregular recruitment.
ROBERTSON (1981) reported similar size differences be- tween populations of Epztonium albidum (Orbigny, 1842) in the British Virgin Islands and Barbados. The largest Virgin Island males were 8 mm long and females ranged to 16 mm. The largest Barbados Island males were 6 mm long while females reached 14 mm although most were 11 mm or less in length.
The northern California population of Epztonium tinc- tum fluctuated in size and abundance more than the south- ern California population and had a definite periodicity. In winter, snail populations declined markedly in the north. Severe winters are known to cause increased mortality in intertidal molluscs unless animals can migrate or are pas- sively washed to deeper waters, or unless they can escape into crevices to hide (CRISP, 1964). Epitonium tinctum was difficult to locate among anemones during winter. It was assumed that most snails were washed off the rocks and died, but others may have escaped and lived out the winter in protected areas. Even if adults do survive the winter months, there is evidence that they may not increase in size appreciably until the spring. Thais (=Nucella) lapillus (Linné, 1758) grows little from October to March (Lar- GEN, 1967), and shell growth in Tegula funebralis ceases completely from November to February (FRANK, 1975). The return of spring signifies a period of larval settlement and the cycle continues. Snails grow during summer and fall until the onset of winter storms. Southern California, in contrast to the north, generally has milder winters, calmer waters, and warmer temperatures. In the southern area it is common to see all stages in the life cycle of a snail throughout the year.
In the north, Epztonium tinctum larvae may survive in
Page 44
Bodega Head
= (o}
a
Snail Length (mm)
The Veliger, Vol. 26, No. 1
JASONDJIFMAMJJASONDJFMAMJJASONDJFMAMJJASONDJFMAMJJA
Carpinteria Beach
= fo)
Snail Length (mm) a
B
JASONDJFMAMJJASONDJSFMAMJSJASONDJFMAMJJASONDJFMAMJJA
= a (o}
= fo} {>}
Number of Snails Collected a °
> Bodega Head
Carpinteria Beach
JASONDJFMAMJJSASONDJFMAMJJSASONDJSFMAMJJASONDJFMAMJJA
1978 1979
1980 1981
Figure 8
Size (including mean and standard deviation) and abundance of snails collected at Bodega Head and Carpinteria Beach from June, 1977, to July, 1981. A. Bodega Head, size. B. Carpinteria Beach, size. C. Bodega Head and
Carpinteria Beach, abundance.
the plankton from late September until settlement, which often occurs as late as June. In the south, young snails and eggs are found throughout the year. Preliminary ob- servations indicate the larvae of E. tinctum grow consid- erably before they undergo metamorphosis. Before hatch- ing, veligers of E. tinctum measure about 70 um in length. In the laboratory we have kept them alive for more than two months, at which time they had attained a size of more than 250 um but had not yet metamorphosed. In the
field the smallest snail observed during more than two years of study was 1.1 mm; apparently, veligers grow considerably in the plankton before they settle. DEHNEL (1955) looked at growth rates of embryos and larvae of northern and southern gastropod populations. He con- cluded that the rates of growth of embryos and larvae in northern gastropod populations are often 2 to 9 times greater than in southern populations of the same species at a given temperature.
C. R. Smith & A. Breyer, 1983
Page 45
Figure 9
Comparison of the largest groups of snails and their associated egg masses found in fall 1980 collections. A. Bodega Head (26 September 1980; SBMNH 33878). B. Carpinteria Beach (23 October 1980; SBMNH 33879).
Once veligers metamorphose, growth in general is faster in warm than in cold seas, but this does not necessarily mean the largest species live in warm seas. The largest snails may be the slow-growing species found in cold water; and within a species, an individual is likely to grow more slowly, but become larger and older, at the northern limits of its distribution (FRANK, 1969). This theory is consistent with our observations. Larger Epitonium tinctum were found north of Bodega Bay in Fort Bragg, and the largest specimens were recorded from Forrester Island, Alaska, the northern limit of distribution for this species.
ACKNOWLEDGMENTS
The authors would like to thank Drs. Roger Seapy, Jo- seph Rosewater, Demorest Davenport, Robert Robertson, James Nybakken, and Diane Perry for critically review- ing the manuscript, and Laurie Marx for preparing the text figures. Dr. Adrian Wenner assisted at all stages with the statistical interpretation. Our special thanks go to Dr. F. G. Hochberg for his continued support and help throughout this study.
LITERATURE CITED
BREYER, A. 1982. Observations on the reproduction, feeding and ecology of the wentletrap Epitonium tinctum (Gastrop- oda: Mesogastropoda). Master’s thesis, Sonoma State Uni- versity. 50 pp.
BULNHEIM, H. P. 1968. Atypische Spermatozoenbildung bei Epitonium tinctum. Ein Beitrag zum Problem des Sperma-
tozoendimorphismus der Prosobranchia. Helgol. Wiss. Meeresunters. 18:232-252.
Cassie, R. M. 1950. The analysis of polymodal frequency distributions by the probability paper method. N.Z. Sci. Rev. 8:89-91.
CassiE, R. M. 1954. Some uses of probability paper in the analysis of size frequency distributions. Aust. J. Mar. and Freshwater Res. 5:513-522.
Cuow, V. 1975. The importance of size in the intertidal dis- tribution of Littorina scutulata. Veliger 18(1):69-78.
Crisp, D. J. 1964. The effects of the severe winter of 1962- 63 on marine life in Britain. J. Anim. Ecol. 33:165-210.
DEHNEL, P. A. 1955. Rates of growth of gastropods as a func- tion of latitude. Physiol. Zool. 28:115-144.
DuSHANE, H. 1979. The family Epitoniidae in the northeast- ern Pacific. Veliger 22(2):91-134.
FRANK, P. W. 1969. Growth rates and longevity of some gas- tropod mollusks on the coral reef at Heron Island. Oecologia 2:232-250.
FRANK, P. W. 1975. Latitudinal variation in the life history features of the black turban snail Tegula funebralis (Proso- branchia: Trochidae). Mar. Biol. 31:181-192.
HarDING, J. P. 1949. The use of probability paper for the graphical analysis of polymodal frequency distributions. J. Mar. Biol. Assoc. U.K. 28:141-153.
HocuBerG, F. G. 1971. Functional morphology and ultra- structure of the proboscis complex of Epitonium tinctum (Gastropoda: Ptenoglossa). ECHO (West. Soc. Malacol.) 4: 22-23.
LarGEN, M. J. 1967. The influence of water temperature upon the life of the dog-whelk Thais lapillus (Gastropoda: Prosobranchia). J. Anim. Ecol. 36:207-214.
NEWELL, G. E. 1964. Physiological variation in intertidal mol- luscs. In: K. M. Wilbur & C. M. Yonge (eds.), Physiology
Page 46
of Mollusca. Vol. 1. Academic Press, New York. pp. 59- 87.
REscH, C. 1972. Chemical recognition of prey in the gastropod Epitonium tinctum (Carpenter). Master’s thesis, Univ. Cal- if., Santa Barbara. 61 pp.
ROBERTSON, R. 1981. Protandry with only one sex change in an Epitonium (Ptenoglossa). Nautilus 95(4):184-186. SMITH, C. REscH. 1977. Chemical recognition of prey by the gastropod Epitonium tinctum (Carpenter, 1864). Veliger
19(3):331-340.
SOKAL, R. R. & F. J. ROHLF. 1969. Biometry. W. H. Free- man, San Francisco. 776 pp.
The Veliger, Vol. 26, No. 1
STRONG, A. M. 1941. Notes on Epitonium (Nitidiscala) tinctum (Carpenter). Nautilus 55(2):46-47.
WENNER, A. M. 1972. Sex ratio as a function of size in marine Crustacea. Am. Nat. 106:321-350.
WENNER, A. M., C. FUsARO & A. OATEN. 1974. Size at onset of sexual maturity and growth rate in crustacean popula- tions. Can. J. Zool. 52:1095-1106.
WEyYMoOuTH, F. W., H. C. MCMILLAN & W. H. RicH. 1931. Latitude and relative growth in the razor clam Siliqua pa- tula. J. Exp. Biol. 8:228-249.
The Veliger 26(1):47-51 (July 1, 1983)
THE VELIGER © CMS, Inc., 1983
The Reproductive Cycle of the Trochid Gastropod
Oxystele variegata (Anton, 1839)
M. A. P. JOSKA ano G. M. BRANCH
Zoology Department, University of Cape Town, Rondebosch. 7700, South Africa
Abstract.
Oxystele variegata (Anton, 1839) is a trochid gastropod found commonly in the southern
African intertidal region. Monthly samples over a one-year period were examined for gonadal devel- opment by comparing dry somatic and gonadal tissue weights and histological sections. Mature oocytes and sperm could be found in monthly samples of the gonads of all animals over 10 mm in size throughout the year, but based on changes in gonadal weights two spawning peaks were detected—one in February and a second in September to October. It seems likely that this temperate species is able to spawn throughout the year but that spawning is intensified during these peak periods.
INTRODUCTION
Oxystele variegata (Anton, 1839) is a trochid gastropod which occurs commonly in the rocky intertidal zone in estuaries and along the southern African coast from south- ern Angola (KENSLEY & PENRITH, 1972) to Durban in South Africa (Day, 1974). It is one of four species in the genus Oxystele that are found in the balanoid zone, where it is very prominent. Because of its abundance O. variegata must be a major contributor to the energy budget of this zone. Based on measurements of the metabolic rate of this species, KING (1974) estimated that the annual population production was 46.4 kJ-m™~?-yr'. McQualb (1980, 1982a) has described how the population of O. variegata is zoned according to size with the largest animals in the upper balanoid zone and the smallest lower on the shore. No attempt has yet been made to ascertain the breeding cycle with any certainty, but McQuarp (1980) hypothesized from settlement patterns that spawning occurred through- out the year, with a peak in February and two smaller peaks in May/June and September/October, 1977. Monodonta lineata, a related trochid of the northern cool temperate regions, has been investigated by DEsaI (1966), who found that this species spawned from May to August with male and female gonads showing similar cycles. UNDERWOOD (1972) investigated the breeding cycle of the British trochids M. lineata, Gibbula umbilicalis, and G. cineraria. He found that M. lineata and G. umbilicalis spawned throughout July and August and less in Septem- ber. However, G. cineraria did not provide clear evidence
of spawning since histological sections of the gonads ap- peared the same throughout the year.
UNDERWOOD (1974) also found that the trochid Auws- trocochlea constricta, which occurs on the west and south- west coast of Australia, did not show any seasonal change in the appearance or histology of the gonad, and he con- cluded that this species spawned throughout the year with a peak in October/November. PAINE (1971), using energy content as a measure of reproductive state, concluded that the western North American trochid Tegula funebralis spawned once a year during the summer.
In this paper a description is given of the breeding cycle of Oxystele variegata, based on changes in the ratio of gonadal/somatic dry weight and gonadal histology during the course of a full year.
MATERIAL ann METHODS
Monthly samples of Oxystele variegata were collected at random from the upper balanoid zone at Dalebrook on the Cape Peninsula (47°07’S, 18°27’E) during the period April, 1980, to March, 1981. The animals were preserved in a 5% formalin solution until they could be examined.
Fifteen to 20 animals of each sex were dissected each month. Every shell was measured across the base at the widest point and the animal was then removed and the operculum cut off and measured. The gonad was dissected out of the somatic tissue and both gonadal and somatic tissue were dried in an oven at 55°C for 24 h. The dry
Page 48
Table 1
Mean monthly shell sizes and opercular diameters of Ox- ystele variegata sampled for gonadal development.
Opercular
Shell size (mm) diameter (mm)
Month 3 Q é g
April, 1980 14.9 14.8 5.4 5.5) May 16.4 16.0 6.0 5.8 June 16.0 16.0 5.8 5.6 August 15.5 16.2 5.4 Dod) September 16.8 16.7 6.0 6.0 October 16.6 16.5 6.0 59) November 16.8 16.4 5.8 5.8 December 15.6 16.0 6.1 59) January, 1981 15.6 15.5 5.6 5.8 February 16.5 16.5 5.9 5.9 March 15.3 16.5 5.4 6.0 Annual mean 16.0 16.1 5.8 5.8
weights of the gonad and of the somatic tissue for each animal were measured.
In addition to the above animals, two to five specimens of each sex were collected each month and used to obtain histological sections of the gonads. The gonads of these preserved specimens were dehydrated in alcohol and blocked in paraffin wax. Transverse sections were cut through the center of the gonads at 10 um. The sections were dehydrated in alcohol and stained with hematoxylin and eosin.
The male and female gonadal weights were linearly regressed on somatic tissue weights for each month. The data obtained from these regressions were used to calcu- late monthly gonadal indices. These indices were defined as the ratio of gonadal to somatic weight, expressed as a percentage for a standard animal of 0.07 g somatic weight (with an opercular diameter averaging 5.8 mm).
RESULTS
All specimens dissected, ranging from 13.6 mm to 21.6 mm shell width, had mature gonads throughout the sam- pling period. Individuals of Oxystele variegata less than 10.0 mm shell width lacked gonads and progressively ‘larg- er gonads could be found in animals with a shell width of 10.0 mm and upwards.
In both males and females of O. variegata the gonads lie adjacent to and above the digestive gland, extending into the shell spiral up to the apex. As with most archaeo- gastropods, trochids release the unfertilized gametes di- rectly to the surrounding environment where fertilization occurs (FRETTER & GRAHAM, 1962; DESAI, 1966; PAINE, 1971; UNDERWOOD, 1972; BRANCH, 1974). Oxystele var- vegata probably conforms to this pattern since we observed no egg laying or egg masses. The male gonad is a pinkish, densely constituted tissue. Histological sections showed that
The Veliger, Vol. 26, No. 1
FEMALE
o +A HA .
oe \ ! 60 somatic weight
0.04 gonadal index 0
0.02 20
is \
J A Ss
gonad weight 0.00
A M J
N
OOL xX anssi} 91eWoSs/peUuoy
0.08
Gonadal & Somatic tissue weights (g)
0.06 gonadal index 0.04 0.02 0.00 1980 1981 Figure 1
Gonadal and somatic dry tissue weights (g) of “standard”? Ox- ystele variegata with an opercular diameter of 5.8 mm and the gonadal index (expressed as a ratio of gonad : somatic weight X 100) plotted against time (month). (Bars indicate 95% confidence levels.)
there were ripe spermatozoa present throughout the year. The ratio of spermatozoa to spermatids and spermatocytes differed from individual to individual in the same month, but spermatozoa never constituted less than 50% of the area of the testis (as determined from grid counts of the gonadal sections). The female gonad contains a mass of white or creamy oocytes, each within a clear jelly coat which is a feature of the trochids (FRETTER & GRAHAM, 1962; Dersal, 1966; DucH, 1969; UNDERWOOD, 1972, 1974; SIMPSON, 1977; WEBBER, 1977; HESLINGA, 1981). Mature oocytes were present throughout the year and had an average diameter of 180 wm, not including the jelly coat. Histological sections showed immature oocytes were also present throughout the year, but not common from January to February or from August to September. No difference existed in mean shell or opercular diameters between the sexes of the animals sampled (Table 1). The gonadal indices show strong correlation between the sexes, both peaking from September to October, 1980,
M. A. P. Joska & G. M. Branch, 1983
Page 49
and in February, 1981, and both dropping in November, 1980, and March, 1981 (Figure 1). Since this gonadal index can be affected by changes in somatic weight, an independent assessment of changes in somatic and gonadal weights was also undertaken. Both gonadal and somatic weights were linearly regressed on opercular diameter for each month. These regressions are shown in Table 2. From these regressions the gonadal and somatic weights of an- imals with a standard opercular diameter of 5.8 mm could be calculated for each month. The somatic weights fluc- tuated about a mean of 0.07 g for each sex. As shown in Figure 1 the somatic weights of both sexes peaked above the mean in September and November and dropped below the mean in April. The gonadal weights of both sexes reflected the gonadal indices almost completely, thus con- firming that in spite of slight changes in the somatic weight the gonadal index is a reliable measure of reproductive activity.
The number of non-significant correlations between go- nadal weight and opercular diameter seen in Table 2 in- dicates a wide “scatter” amongst the population in certain months, particularly the males. This scatter is due to the fact that some individuals are sexually mature at a time when others have just spawned. Again, however, there was a strong correlation between the sexes for both the gonadal and somatic tissue weights, and we are confident that the gonadal index and changes of gonadal weights do reflect reproductive cycles.
DISCUSSION
It appears that Oxystele variegata, as with some other tro- chids (UNDERWOOD, 1972, 1974; SIMPSON, 1977) exhibits continuous gametogenesis once mature. Synchronization of spawning still remains important since fertilization is external and, indeed, the male and female gonadal weights do peak and fall in unison (Figure 1). Oxystele variegata congregates in large numbers in the upper balanoid zone at Dalebrook thus also ensuring proximity of the sexes during spawning. DeEsal (1966), DucH (1969), and SIMPSON (1977) also found this clustering behavior in tro- chids.
Despite this, the gonadal tissue weights (relative to opercular diameter) showed marked variation between in- dividuals, particularly around the periods of peak spawn- ing. However, in all samples dissected during other months there were always some specimens whose gonadal weights were well above or below the average and these were considered to be in pre- or postspawn states respectively. Such variation in the gonadal weights within the popu- lation probably indicates that there are some individuals that spawn out of phase with the bulk of the population. The presence of some spawned individuals in virtually every month of the year suggests that spawning occurs year round although peaking twice a year. These varia- tions in gonadal weight are reflected in the number of months in which there were non-significant correlations
between gonadal weights and opercular diameter (Table 2), in contrast to the generally high correlations between somatic tissue weight and opercular diameter. The two main gonadal peaks indicate spring and late summer spawnings with the build up to the spring spawning (Sep- tember to October) being more prolonged. At present we have no evidence whether these peaks repeat each year.
It is also apparent from the histological sections, which showed a constant supply of ripe ova and sperm in the gonads, and from the irregular but continuous settlement of recruits to the low shore (McQualp, 1982b), that spawning probably occurs throughout the year, peaking in the spring and late summer.
The somatic tissue weights of standard-sized animals of both sexes remained steady at a mean of 0.07 g, except for April when they declined. This fall in somatic weight is possibly because during this period there is a recruit- ment of new individuals to this zone (McQuaIp, 1982b) and we speculate that increased feeding competition may strain existing food sources. By May to June the popu- lation has declined due to mortality and the somatic weight increases (Figure 1) together with new algal growth in autumn. In the upper balanoid zone, from where our sam- ples were taken, there are only two main macroalgae— Porphyra capensis and Gelidium pristoides. MCQUAID (1980) found that both these species have varied calorific values during the year. Porphyra capensis declined in cal- orific value during autumn whilst G. pristoides had a max- imum value in autumn. The drop in calorific value of some of the food available for Oxystele variegata could affect the somatic weights, but we found that O. variegata were not commonly seen on macroalgae, and they possibly mainly feed on microalgae and sporelings rasped from the substratum. This is also the opinion of McQualp (1982a). A drop in the number of sporelings has been found during April in an analysis of monthly colonization carried out by Joska (in preparation) and this, too, could explain the lower somatic weight during this month.
In archaeogastropods the larval stage is brief (FRETTER & GRAHAM, 1962; DEsal, 1966; UNDERWOOD, 1972; WEBBER, 1977) and settlement on the shore should take place within a week of spawning. McQualip (1982a, b) found that 5 to 6-mm specimens of O. variegata were de- tectable in large numbers in February with a smaller peak in June/July. In addition, small numbers could be found throughout the year. Since specimens of O. variegata take about four months to reach a size of 5 to 6 mm, these juveniles probably settled about four months earlier, and are likely to have been the result of, respectively, the spring and late summer spawnings that we have recorded.
Temperature is a factor often cited as being of great importance for spawning or reproduction in marine in- vertebrates. During the period of sampling the sea tem- peratures rose during the spring spawning but fell at the time of the late summer spawning (Figure 2). Apart from suggesting that a minimum temperature exists for spawn- ing, there is no obvious influence of temperature on the
Page 50 The Veliger, Vol. 26, No. 1
Table 2
Regression coefficients for regressions of gonad weight (y) on operculum diameter (x): y = a) + a,x and coefficients of determination (r’) with the probability that r? is significant (P).
Month ao a, ie P g April, 1980 —0.0155 0.0382 0.2729 0.05 May —0.0340 0.0794 0.4638 0.001 June —0.0152 0.0436 0.2915 0.05 August 0.0194 —0.0046 0.0026 Not significant September —0.0290 0.1103 0.2988 0.01 October —0.0034 0.0630 0.0232 Not significant November —0.0252 0.0672 0.3400 0.01 December —0.0093 0.0399 0.2495 0.05 January, 1981 0.0058 0.0251 0.0214 Not significant February —0.0676 0.1691 0.5365 0.001 March : —0.0281 0.0666 0.5426 0.001 ) April, 1980 —0.0222 0.0531 0.1509 Not significant May : 0.0374 - =0,0317/ 0.0228 Not significant June —0.0661 0.1363 0.5817 0.001 August —0.0017 0.0439 0.1618 Not significant September —0.0310 0.1093 0.1910 0.05 October —0.0195 0.0870 0.1710 0.05 November —0.0152 0.0535 0.4046 0.01 December 0.0020 0.0231 0.1047 Not significant January, 1981 —0.0239 0.0707 0.1925 0.05 February —0.0820 0.1823 0.6314 0.01 March —0.0156 0.0433 0.0940 Not significant
Regression coefficients for regressions of somatic tissue weight (y) on operculum diameter (x): y = a, + a,x and coefficients of determination (r?) with the probability that r* is significant (P).
Month Aly ay r? P g April, 1980 0.0346 0.0317 0.9934 0.001 May —0.1638 0.4054 0.8411 0.001 June —0.0601 0.2269 0.4540 0.01 August 0.0622 0.0144 0.0049 Not significant September —0.0863 0.2825 0.7607 0.001 October —0.1844 0.4410 0.7384 0.001 November —0.0926 0.2923 0.5173 0.001 December —0.0940 0.2788 0.4958 0.001 January, 1981 —0.1105 0.3049 0.7235 0.001 February —0.1199 0.3335 0.5736 0.001 March : —0.1688 0.4166 0.8663 0.001 ) April, 1980 —0.0229 0.1282 0.4085 0.01 May —0.0199 0.1610 0.2331 0.05 June —0.1480 0.3823 0.5455 0.001 August 0.0370 0.0659 0.1417 Not significant September —0.1046 0.3129 0.6867 0.001 October =O1B27 © 0.3571 0.8634 0.001 November —0.0941 0.2979 0.6955 0.001 December —0.0296 0.1709 0.5703 0.001 January, 1981 —0.0758 0.2295 0.6760 0.001 February —0.1319 0.3389 0.8117 0.001
March 0) UZS7/ 0.3222 0.5280 0,001
M.A. P. Joska & G. M. Branch, 1983
Page 51
24 om O — ¢ 5 20 — 0 hh o a — 16 o ~~ 0 o YM 12
= 1980 1981
Figure 2
Mean monthly sea temperatures during the sampling period. Bars indicate maximum and minimum temperatures. (Temper- ature records kindly supplied by the Department of Maritime Defence, Simonstown.)
reproductive cycle in this species. Dalebrook lies in False Bay, which because of its shallow waters and current pat- terns affords year round moderate conditions and pre- dictable seasonal changes in temperature. Rather more variant conditions on the west coast could possibly pro- duce different spawning peaks.
ACKNOWLEDGMENTS
We would like to thank Dr. John Pearse for his pains- taking criticism of an earlier manuscript of this paper. The research was supported by a grant from the South African Committee for Oceanographic Research.
LITERATURE CITED
BRANCH, G. M. 1974. Ecology of Patella Linnaeus from the Cape Peninsula, South Africa. 2. Reproductive cycles. Trans. R. Soc. S. Afr. 41(2):111-160.
Day, J. H. 1974. A guide to marine life on South African shores. A. A. Balkema, Cape Town. 300 pp.
Desai, B. N. 1966. The biology of Monodonta lineata (Da Costa) Proc. Malac. Soc. Lond. 37:1-17.
Ducu, T. M. 1969. Spawning and development in the trochid gastropod ELuchelus gemmatus (Gould, 1841) in the Hawai- ian Islands. Veliger 11(4):415-417.
FRETTER, V. & A. GRAHAM. 1962. British prosobranch mol- luscs. Ray Society, London. 755 pp.
HEsLINGA, G. A. 1981. Larval development, settlement and metamorphosis of the tropical gastropod Trochus niloticus. Malacologia 20(2):349-357.
KENSLEY, B. & M.-L. PENRITH. 1972. Monodonta (Oxystele) fulgurata Philippi, a synonym of Oxystele variegata (Anton). J. Conchol. 27:349-352.
KING, J. M. 1974. Population respiration of Oxystele variegata (Gastropoda). Zoology Honours Project, University of Cape Town.
McQuaip, C. D. 1980. Spatial and temporal variations in rocky intertidal communities. Doctoral thesis, Zoology, Uni- versity of Cape Town.
McQuaip, C.D. 1982a. The influence of desiccation and pre- dation on vertical size gradients in populations of the gas- tropod Oxystele variegata (Anton) on an exposed rocky shore. Oecologia 53:123-127.
McQuaip, C. D. 1982b. Population dynamics and growth of the gastropod Oxystele variegata (Anton) on an exposed rocky shore. S. Afr. J. Zool. 18:56-61.
PAINE, R. T. 1971. Energy flow in a natural population of the herbivorous gastropod Jegula funebralis. Limnol. Oceanogr. 16(1):86-98.
SIMPSON, R. D. 1977. The reproduction of some littoral mol- luscs from Macquarie Island (Sub-Antarctic). Mar. Biol. 44:125-142.
UNDERWOOD, A. J. 1972. Observations on the reproductive cycles of Monodonta lineata, Gibbula umbilicalis and G. cine- raria. Mar. Biol. 17:333-340.
UNDERWOOD, A. J. 1974. The reproductive cycles and geo- graphical distribution of some common eastern Australian prosobranchs (Mollusca:Gastropoda). Aust. J. Mar. Fresh- water Res. 25:63-88.
WEBBER, H. H. 1977. Gastropoda:Prosobranchia. In: A. C. Giese & J. S. Pearse (eds.), Reproduction of marine inver- tebrates. Academic Press, New York. pp 1-114.
The Veliger 26(1):52-61 (July 1, 1983)
THE VELIGER © CMS, Inc., 1983
The Larval Biology of Brachidontes modiolus (Linné, 1767) (Bivalvia: Mytilidae)
ANGELA FIELDS anp EUNA MOORE
Department of Biology, University of the West Indies, Cave Hill, Barbados
Abstract. Larvae of Brachidontes modiolus were reared in the laboratory from eggs through to settled juveniles. Egg sizes ranged between 67.3 and 77 um. Straight-hinge veligers appeared 15 to 17 h after fertilization of the eggs. The length of shelled larvae increased from 96 to 221 um: the straight-hinge stage from 96 to 176 um, the umbo stage from 168 to 221 um, and the pediveliger stage from 180 to 221 um. Settlement occurred at lengths of 180 um and upwards. The larval hinge consists of small teeth along the length of the hinge with larger teeth at both ends. Larvae of B. modiolus develop more rapidly and settle at an earlier age than larvae of B. recurvus and B. granulata.
INTRODUCTION
Brachidontes modiolus (Linné, 1767) (=B. citrinus) is a small marine mytilid, the adults of which measure be- tween 38 mm (ABBOTT, 1974) and 46 mm (MCLEAN, 1951). The geographic range for this species is from Flor- ida to the West Indies (ABBOTT, 1974). In Barbados, members of this sublittoral species may be found recessed within beds of the seagrass Thalassia testudinum Konig or attached to the rocky surface of reef flats at depths of O- 2 m. Brachidontes modiolus is highly gregarious and, whether living epifaunally or infaunally, occurs in dense aggregates of individuals.
The specific name Brachidontes citrinus (Réding, 1798) has been widely used. ABBOTT (1974), however, consid- ered this to be a synonym of B. modiolus (Linné, 1767). Indeed the name ‘modiolus’ is singularly apt, for B. mo- diolus exhibits characteristics of the Modiolus group of mytilids, namely the possession of subterminal umbones and a shell shape which is more conical than triangular (STANLEY, 1970, 1972).
The larval biology of Brachidontes modtolus has hitherto been unreported in the literature under any of its syn- onyms. A knowledge of the duration of the planktonic stage of an aquatic larva, the time during which it is exposed to ocean or coastal currents, could contribute to an understanding of the distribution of a species in a given region. This aspect has been discussed by COE (1953) and SCHELTEMA (1971). In addition, a description of the larval stages of B. modiolus would aid in the identification of these larvae when encountered in plankton samples, as
well as establish the life history pattern and strategy of the species.
The identification of bivalve larvae has posed problems in the past. LOOSANOFF et al. (1966) drew attention to the inadequacy of “indirect methods” of identification of bi- valve larvae, and pointed out that these methods have led to discrepancies in the description of larvae of the same species when reported by different authors. Indirect meth- ods include monitoring the development of an unidentified larva found in the plankton through to settling and the assumption of identifiable features of a particular species. These authors recommend “direct methods” of identifi- cation, 1.e., the rearing of larvae from fertilized egg stage through to metamorphosis under controlled laboratory conditions. The development of reliable methods for ob- taining viable gametes and for the rearing of juveniles has resulted in the successful culture of the larvae of several marine bivalves. LOOSANOFF & Davis (1963) reviewed methods for the cultivation of larvae and detailed the spe- cific requirements necessary for the successful culture of 19 species of bivalves. As characters to be used in the identification of marine bivalve larvae, LOOSANOFF e¢ al. (1966) listed the dimensions of the larval shell (the pro- dissoconch), its general shape, prominence of the umbones during growth to metamorphosis, and ratios of length of hinge to maximum length or width of shell. CHANLEY & ANDREWS (1971) and CHANLEY & CHANLEY (1980) pro- vided useful terminology for describing larval shell form and, in order to provide a better description of larval shell length, height and depth relationships. LOOSANOFF et al. (1966) provided a guide to the dimensions and shapes of
A. Fields & E. Moore, 1983
Page 53
20 species of bivalves, and CHANLEY (1970) gave a review of the larval characteristics of the Mytilidae. Within the genus Brachidontes, descriptions of the larvae of B. recur- vus from the western North Atlantic Ocean have been published in CHANLEY (1970), and of B. granulata from central Chile in CAMPos & RAMORINO (1980). The lar- vae of B. senhausi were described in YOSHIDA (1937), but according to KURODA ef al. (1971; cited in CAMPos & RAMORINO, 1980), this species belongs to the genus Mus- culus.
The purpose of this paper is to provide a description of the larval stages of Brachidontes modiolus, with informa- tion on the development and length of the larval life of the species.
MATERIALS anp METHODS
Gametes were obtained from ripe mussels collected during the peak of the reproductive season (June to September). This peak was determined by continuous sampling and histological techniques over a period of two years. In the laboratory the animals were cleaned of sediment and en- crustations and placed in freshly collected sea water. Ini- tially, several methods were employed in an attempt to obtain viable gametes:
(1) temperature shock within the range 24—34°C;
(2) pricking of the posterior adductor muscles of the adults; (3) introduction of sperm and/or eggs obtained from stripped gonads to water containing ripe mussels;
(4) treatment of stripped gonads with a 0.1 N solution of ammonium hydroxide;
(5) exposing the mussels to hydrogen peroxide in alkaline (pH 9.1) sea water as per Morsk et al. (1977). Only this last method was successful; hence, the procedure is detailed below.
Alkaline sea water was prepared with predetermined quantities of Trizma*, hydrochloric acid and natural sea water (pH 7.2). Three or four mussels were placed in- dividually or collectively in beakers containing 50 ml of alkaline sea water per animal (pH 9.1); hydrogen per- oxide was then added with a micropipette to a final con- centration of 5mM. This was the treatment solution. The animals were kept in this solution for one hour, after which time the liquid was decanted and replaced with 100 ml of fresh treatment solution. One hour after the second treatment, the mussels were removed from the al- kaline sea water, rinsed, and placed in beakers containing 100 ml of natural sea water. These were then placed in a water bath at a temperature of 33-34°C. Males and females received the same treatment. The onset time of spawning varied widely, from 30 minutes to several hours after treatment in the hydrogen peroxide solution. Mus-
* A brand name. Use here does not necessarily imply endorse- ment of the product.
sels seen spawning were removed and placed individually in beakers containing natural sea water at 28°C. The eggs were rinsed thoroughly with sea water filtered through glass fiber filter paper. Sperm was added to the egg sus- pension, and the two allowed to remain undisturbed for 10 min to encourage fertilization. In some instances a female in the process of spawning was placed in a weak sperm suspension, and so the eggs were fertilized as they were extruded. The fertilized eggs were rinsed to remove excess sperm and placed in 150 ml of filtered sea water in Erlenmeyer flasks of 250 ml capacity. Possible contam- ination of the cultures was reduced by placing tissue paper in the necks of the flasks and covering the opening of the flask with aluminum foil. If flasks containing larvae were left open to the air, a dense population of ciliates soon developed, with consequent death of the larvae. The em- bryos were left undisturbed for 24 h, at which time the strongly swimming larvae were pipetted off and intro- duced into fresh sea water to a density of 25-30 larvae/ ml. The water containing the larvae thereafter was changed every third day. This was achieved by washing the larvae over a fine nylon mesh which was glued securely over one end of a large open-ended glass tube. Mortality of the larvae during washing was reduced if the mesh was held in a beaker containing filtered sea water, so that the mesh was positioned below the surface of the water. ‘The bottom layer of water in the flask was discarded as dead or weak larvae accumulated there. The flasks were thoroughly washed at each water change, and care was taken to en- sure that no detergents contaminated the sea water. The sea water used for each change was freshly collected and filtered. Best survival rates were obtained when the larvae were reared in unaerated sea water.
The larvae remained unfed for 48 h and thereafter were fed on a mixture of Dunaliella tertiolecta and Nephroselmis tibron. When possible, /sochrysis galbana was added to the diet. Feeding densities in the case of the larger alga, z.e., Dunaliella, was approximately 8000-10,000 cells per ml of culture solution. Concentrations of the smaller alga were higher, 70,000-80,000 per ml of culture solution. Algal concentrations of these magnitudes were cleared by the larvae in 24 h.
Sub-samples of approximately 10 larvae were mea- sured every two days for two weeks. Length was measured as the maximum distance in the antero-posterior direction, height as the maximum distance from the hinge to the ventral margin of the shell, and depth as the maximum left-right dimension (CHANLEY, 1970).
RESULTS
The eggs of Brachidontes modiolus ranged in diameter from 67.3-77 wm, and were a uniform dark brown in color. When spawned, the eggs had an irregular appearance but soon became rounded. No measurements were made of the spermatozoa. The sperm obtained from stripped go-
Page 54 The Veliger, Vol. 26, No. 1
A. Fields & E. Moore, 1983
Page 55
nads appeared less active than those obtained through the mediation of hydrogen peroxide.
As in BAYNE (1965), the stages chosen to evaluate de- velopment times to the straight-hinge stage were those easily recognized and not those with particular embryo- logical significance (Table 1).
Stage 1—First division: the time at which 50% of the sam- ple had undergone first cleavage.
Stage 2—The ciliated blastula: first appearance of cilia, evidenced by slowly rotating larvae (Figure 1a).
Stage 3—The early trochophore: appearance of an apical flagellum (Figure 1b).
Stage 4—Veliger: appearance of long cilia on the apical plate (Figure Ic).
Stage 5—Transitional stage: first appearance of the shell as a transparent object on the dorsal surface of the larva (Figure 1d).
Stage 6—Straight-hinge veliger: the possession of a com- plete shell, the prodissoconch. Very early straight-hinge veligers are darker than the later ones (Figure le).
First division occurred approximately 36 min after fer- tilization and the ciliated blastula appeared 3 h later. The ciliated blastulae swam slowly at first and as time pro- gressed swam upwards towards the surface of the water column. Development of the trochophore occurred 5 h after fertilization, and veligers were first seen 4 h later. Transitional stages between the veliger and the straight- hinge veliger appeared 12 h from zero time, and straight- hinge veligers were seen in cultures 15-17 h after fertil- ization. The color of the larvae underwent a change during development, and stages 1 through 5 were dark brown while stage 6, the straight-hinge veliger, was a pale yellow-brown.
The rate of development of the larvae varied with tem- perature. Larvae reared at 34°C developed into straight- hinge veligers 13 h after fertilization. In cultures kept at 24°C, it was not until 25 h had elapsed that straight-hinge veligers were observed. At the time that straight-hinge veligers were recorded from cultures reared at 28°, 32° and 34°C (7.e., between 13-17 h), larvae reared at 24°C were still at the early trochophore stage.
Larval Dimensions and Shape
The early straight-hinge larvae measure 96 um in length, with a minimum height of 67 wm. No measurement of depth was recorded at the earliest straight-hinge stage. The smallest depth recorded was 56 um at a larval length
Table 1
Summary of the observed development times of the larvae of Brachidontes modiolus. Temperature = 28°C.
Stage Description Time 0 Fertilization 0 1 First division 34-36 min 2 Ciliated blastula 3h 40 min 3 Early trochophore 5 h 15 min 4 Veliger 9h 15 min 5 Transitional stage 12h 6 Straight-hinge veliger 15-17 h
of 152 wm. Straight-hinge larvae attained a size of up to 176 um in 6 days. Heights then ranged from 126-144 um, and depths from 84-104 wm. At lengths greater than 176 um the hinge line invariably showed signs of rounding (Figure 2). Lengths increased faster than height, which in turn increased faster than depth. Between lengths of 96 and 115 wm, heights were 19-29 um less than length, while at a length of 176 um, heights measured 32-50 um less than length. The first indication of umbo development appeared at 168 wm, with heights ranging from 120-136 um and depths from 72-88 um. All observed combinations of larval heights and depths for a given length are given in Figure 3. The length of the hinge at a shell length of 152 um was 120 um, increasing to 128 um at a shell length of 168 wm. The results are summarized in Table 2 and Figure 2.
The straight-hinge larva is roughly ““D” shaped. The hinge line is long relative to the length of the shell. The shoulders slope steeply, with the posterior shoulder short- er and sloping more steeply than the anterior. The pos- terior end is higher and more pointed than the anterior. The ventral margin of the shell is rounded. The hinge line becomes slightly rounded with the development of the umbo, and is at first “round” or “indistinct.”” The umbo may remain low and not clearly defined through lengths of 168-288 wm, becoming “broadly rounded” in later stages. The minimum length at which the umbo was seen to project above the shell margin is 240 wm. The shoulders at this stage are almost straight, the anterior shoulder not sloping as steeply as the posterior. The ventral margin is now markedly elongate, but still rounded. The larval hinge consists of a series of small teeth, fanked by two or three larger teeth.
Figure 1
Stages in the early larval development of Brachidontes modiolus. A. ciliated blastula; B. early trochophore; C. veliger;
D. transitional stage; E. straight-hinge stage.
Page 56
A B 120 x82
E 191 « 146
I 224 x 184
150 x 109
208 x 176
ithe Veligers Volk ZomNomi
Cc D 159x118 173 x 137
218 x 182
J 282 « 264
Figure 2
The larvae of Brachidontes modiolus at different stages of development from the early straight-hinge stage (A) to settlement (G-I). Larvae are positioned with anterior end to the left, except in J. The larva in J is an early juvenile just beginning dissoconch growth. The length and height of the larvae are indicated under each photograph;
measurements are in microns.
The smallest pediveliger larva seen using its foot mea- sured 180 wm (Figure 4) in length, but more generally, ambulatory pediveligers appeared at a length of 184 um. The eye spot first appeared in larvae at length 184 um when cultured at temperatures of 32° and 34°C.
Internal Anatomy of the Larvae
The internal anatomy of the larva was at first indistinct at magnifications of up to 500X. The gut became apparent on the first day as a straight tube running in a posterior
direction. It soon became coiled (Figure 5a). The digestive gland soon became easily visible, as with the onset of feed- ing in the larvae, the organ developed a green-brown color (Figure 5b). The adductor muscles showed clearly by the third day, and the velar retractor muscles were also con- spicuous at this time. The foot was fully developed by day 6, with the pedal retractor muscles clearly visible (Figure 5c, d). The velum increased in size with the development of the larva to the pediveliger stage, and occupied a large portion of the shell cavity. The gill filaments were not clearly visible until after metamorphosis (Figure 5e). The
A. Fields & E. Moore, 1983
Rage y),
Figure 3
Larval dimensions of Brachidontes modiolus. The height and depth co-ordinates run parallel to the length axis. The dots represent length-depth or length-height measurements. The lines enclosing the dots were fitted by eye and represent maximum and minimum height and depth measurements. The three-dimensional figure represents all possible length, height, and depth combinations for B. modiolus (after CHANLEY & VAN ENGEL, 1969). The clear area represents the straight-hinge stage, the lined area the umbo stages, and the stippled area, the transitional stage
between straight-hinge and umbo forms.
larvae of Brachidontes modvolus settled at sizes between 180 and 221 um in length and settlement occurred from day 11 onward, although swimming larvae were still vis- ible in the medium up to the 30th day.
DISCUSSION Induction of Spawning
LOOSANOFF & Davis (1963) list methods used in the induction of spawning in 19 bivalves. They pointed out that where some species responded to thermofluctuation as a stimulus to spawning, others needed the additional stimulus of a sperm or egg suspension. In some instances special methods had to be employed, such as pricking the
Table 2
Summary of larval dimensions of Brachidontes modiolus.
Length Height Depth Stage (um) (um) (um) Early straight-hinge stage 96 76 2 Straight-hinge stage 96-176 67-152 *_100 First indication of umbo 168 120-136 72-88 Umbo stage 168-221 120-184 72-124
* Not measured.
Page 58
The Veliger, Vol. 26, No. 1
Figure 4
Pediveliger of Brachidontes modiolus.
adductor muscle in Mytilus edulis. Other species, like Modiolus demissus, did not respond to any treatment; LOOSANOFF & Davis (1963) were unsuccessful in induc- ing this species to spawn. WILSON & HODGKIN (1967) failed to induce spawning of Brachidontes cf. variabilis in the laboratory. CHANLEY (1970) was finally successful in causing spawning in B. recurvus by placing the mussels in sea water with temperatures fluctuating between 20 and 32°C. Previous attempts to induce spawning in this animal, by adding stripped gametes to the water or stretching or injuring the adductor muscles, had proved unsuccessful. Ripe adults of B. granulata spawned when placed in filtered sea water at 16°C after being held in an incubator at 6°C for 12 h. The account presented above demonstrates the individuality of the response of different species to various spawning stimuli.
Stripping of the gonad of Brachidontes modiolus failed to produce viable gametes for the same reason that the eggs obtained through the mediation of 0.5 M KCl are not fertilizable. RAVEN (1958) stated that maturation of the eggs of most mollusks may begin spontaneously, in- dependent of fertilization, e.g., after spawning in sea water, and continues until metaphase of the first maturation di- vision. Unfertilized eggs are blocked at this stage. Matu- ration is evidenced in part by the dissolution of the ger- minal vesicle. The ova of B. modiolus are not mature while still in the gonad. Eggs from this species, when obtained by stripping or by injection of KCl, possessed an intact germinal vesicle and were therefore immature and were incapable of being fertilized without further treatment (e.g., the addition of NH,OH). In contrast, the eggs extruded from mussels stimulated by the addition of hydrogen per-
oxide had started the maturation process and were easily fertilizable.
Mors et al. (1977) found that the hydrogen peroxide- induced spawning of the abalone Haliotis rufescens may have resulted from a “direct activation of the enzyme- catalyzed synthesis of prostaglandin endoperoxide.” Pros- taglandin endoperoxide (PGEP) is produced from arachi- donic acid through a series of reactions, the first step of which is catalyzed by the enzyme fatty acid cyclooxygen- ase (=PGEP synthetase). These investigators showed that abalone eggs and gonads from ripe animals of both sexes contained large quantities of cyclooxygenase, and further that hydrogen peroxide directly increased the rate of the reaction catalyzed by the PGEP-forming cyclooxygenase from reproductive cells of the abalone. PGEP synthetase has been implicated in the control of spawning not only in abalones, but in Mytilus californianus (MORSE et al., 1977) and sea urchins (MorsE et al., 1978). It is probable that a similar control of spawning exists in Brachidontes modiolus. IWATA (1952) found that electrical stimulation induced maturation of eggs of Mytzlus edulis. He suggested that the stimulus was mediated by the ovary, probably by the secretion of some substance that caused the ova to mature. According to IWATA (1952), spawning in Mytilus appeared to follow automatically as soon as the eggs begin the maturation division, and therefore spawning in this animal depended entirely on whether the maturation pro- cess had taken place. A number of questions arise from a comparison of the results of MorsE et al. (1977) and Iwa- TA (1952). Could the proposed substance of Iwata (1952) be related to PGEP synthetase, or to any of the enzymes or intermediate products of PGEP production? Converse- ly, does PGEP synthetase act to promote maturation of oocytes and hence spawning?
The role of PGEP synthetase in the control of spawning in Brachidontes modiolus would be of interest for further study. Morse et al. (1977) stated that the fatty acid-cy- clooxygenase reaction may be potentially rate-limiting in the physiological sequence of reactions leading to spawn- ing and therefore possibly under hormonal and/or neural control. Thus a knowledge of the levels of this enzyme in B. modiolus, together with information on environmental factors, could help in determining the ultimate factors con- trolling the release of gametes in this species.
Larval Survival and Development
Larvae survived well in unaerated cultures, and change of water every third day proved adequate for removing toxic waste products before harmful levels were reached. Some morphological malformations were observed in some of the larvae, for example concavity of the hinge line or un-equal valve growth; but it could not be determined to what extent these were due to culture conditions. Abnor- mality of the hinge line as seen in Brachidontes modiolus was also reported for other bivalves (LOOSANOFF & DAVIS, 1963). In addition, these authors described another type
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PAM
AAM
Figure 5
Diagrams of conspicuous features of the internal anatomy of Brachidontes modtolus. a. straight-hinge veliger; b. 3- day old larva; c and d. 6-day old larvae; e. spat. Scale bar for a, b, c, and d is 40 um long; for e, it is 60 wm long. AAM, anterior adductor muscle; DG, digestive gland; ES, eye spot; F, foot; Gi, gills; I, intestine; PAM, posterior adductor muscle; PRM, pedal retractor muscle; St, stomach; U, umbo; V, velum.
of larval abnormality in which there was no clear-cut anatomical malformation, but rather the larvae were un- able to feed. Such larvae developed to the straight-hinge stage but grew no further and eventually died. It is prob- able that the larvae found in the bottom layers of cultures of B. modiolus suffered from this type of “feeding” abnor- mality. LOOSANOFF & Davis (1963) reported that this type of abnormality in Mercenaria mercenaria was related
in some instances to the type of food fed to the larvae. This aspect was not investigated in B. modiolus.
That larvae of various species of bivalves show variation in growth rate among individuals reared from the same spawn under similar conditions is well established (LOOSANOFF & Davis, 1963). In addition to individual