MBL/WHOl THE NAUTILUS Volume 106 1992-1993 AUTHOR INDEX Askew, T. M 130 Bailey, J. F 60 RiELER, R 15 Ross, K. J 21 Emerson, \V. K 39, 147 eversole, .\. g 119 Goodfriend, G. a 55 CioODSELL, J. G. 119 I I.^HASEWYCH, M. G 1, 43, 130 Healy, J. M 1 Hunter, R. U 60 KooL, S. P 21 Marshall, B .^ 24 McLean. J. H 39,115,125 Oleinik, a. E 137 Petit, RE 43 Petuch, E. J 68 Potter, E, 72 QuiNN. J. E, Jr 50. 77 Rehder, ha 123, 127 Rex, ma 72 Tucker, J K 76 Verhecken, a 43 NEW TAXA PROPOSED IN VOLUME 106 (1992-1993) n. sp. GASTROPODA Pleurotoniariidae Pcrotrochtis maureri Harasew\cli & Askew, 1993, n C'lypeosectidae Pseitdorimula inidatlaniica McLean, 1992 Trocliidae Calliostomii allfrninn Ouiiin, 1992, n. sp. Calliostoma argcnlinn Ouiiin, 1992, n. sp. CallioHloma atlanluidcs Quinn, 1992, n. sp. C'.aUiostoina aiilicurn Quitin, 1992, n. sp. CUilliosliima axclolsaoni Quinn, 1992, n. n. C'allioslotrm hcnmidcnsc Qninn, 1992, n. sp- CaUiofitunia brunncopictum Quinn, 1992, n. sp Calliostoma cnidophiluni Quinn, 1992, n. sp. Calliostoma coronatum Quinn, 1992, n. sp. Calliostoma citbensc Quinn, 1992, n. sp Calliostoma debilc Quinn, 1992, n. sp Calliostoma denlalum Quinn, 1992, n. sp. Calliostoma furosnm Quinn, 1992, n. sp. . . Calliostoma gncsti Quinn, 1992, n. sp. ... Calliostoma hilarc Quiiui, 1992, n. sp. Calliostoma hirlum Quiiui, 1992, n. sp. Calliostoma moscaltetlii Quinn, 1992, n. sp. Calliostoma purpureiim Quinn, 1992, n. sp. Calliostoma rota Quinn, 1992, n. sp. Calliostoma rude Quiiwi, 1992, n. sp Calliostoma rngosum Quinn, 1992, n. sp. CUilliostoma sralrnum Quiiui, 1992, n. sp. Calliostoma snirra Quinn. 1992, n. sp. Calliostoma semisuavc Quinn, 1992, n sp Calliostoma serratulum Quinn, 1992, n. sp. Calliostoma tenebrosum Quinn, 1992, n. sp. Calliostoma vinosum Quinn, 1992, n. sp Calliostoma viscardii Quinn, 1992^ n. sp. Solariella cristata Quiiui, 1992, n sp. Solariella quadricincta Quinn, 1992, Solariella slaminea Quinn, 1992, ii. sp 130 115 96 103 102 97 105 86 85 83 102 93 90 87 95 106 78 97 87 95 100 83 103 92 110 85 78 87 96 85 52 50 53 Colunibellidae Cotonopsis monfilsi Emerson, 1993, n. sp 147 Faseiolariidae Buccinofiisus patuxcntensis Petuch, 1993, n. sp. 165 Meloiigenidae Bustjcotyptis choptankensis Petuch, 1993, n. sp. 166 Tiirrifulgur manjlandicus Petuch, 1993, n. sp. 166 Turrifulgur prunicola Petuch, 1993, n. sp. 167 Thaidinae Ecphora (Ecphora) chesapeakensis Petuch, 1992, n. sp. 68 Ecphora (Ecphora) turneri Petuch, 1992, n. sp. 70 Ecphora (Trisecphora) scientisensis Petuch, 1992, n. sp. 70 Ecphorosycon lindajoyceac Petucli, 1993, n. sp. 164 Muricidae Patuxentrophon Petuch, 1993, n gen 165 Volutidae Ftilgoraria (Musashia) novoilpinica Oleinik, 1993, n. sp. 138 Ftilgoraria (Musashia) genuata Oleinik, 1993, n sp. 140 Fnlgoraria (Musashia) cordata Oleinik, 1993, n. sp. 140 Fulgoraria (Musashia) lilitschikensis Oleinik, 1993, n. sp. 140 Harpidae Harpa cabriti Relider, 1992 n. n 124 Harpa goodtvini Rehder, 1993, n, sp 127 Gancellariidae Trilonoharpa leali Harasew \ch. Petit & \ erhecken, 1992, n. sp 45 Cancellaria petuchi Harasewych, Petit & Verhecken, 1992, ii..sp ' 47 Turridae Buridrillia dcrmjorum Emerson & McLean, 1992, n. sp. 39 Calverturris Petuch. 1993, n. gen. 167 Calverturris schmidti Petuch, 1993, n. sp 168 Drillia macleani Tucker, 1992, n. n 76 Transmariaturris Petuch, 1993, n. gen 168 Helminthoglyptidae Hemitrochus bowdcncnsis (Jncidfriend. 1992, n. sp. 55 rHE NAUTILUS Volume 106, Number 1 February 27, 1992 ISSN 0028-1344 A quarterly devoted to malacology. Dry MR 6 my f i ^^' Hole, Mass. J EDITOR-IN-CHIEF Dr. M. G. Harasewych Division of Mollusks National Museum of Natural History Smithsonian Institution Washington, DC 20560 ASSOCIATE EDITOR Dr. R. Tucker Abbott American Malacologists, Inc. P.O. Box 2255 Melbourne, FL 32902 CONSULTING EDITORS Dr. Rudiger Bieler Department of Invertebrates Field Museum of Natural History Chicago, IL 60605 Dr. Robert T. Dillon, Jr. Department of Biology College of Charleston Charleston, SC 29424 Dr. William K. Emerson Department of Living Invertebrates The American Museum of Natural History New York, NY 10024 Mr. Samuel L. H. Fuller 1053 Mapleton Avenue Suffield, CT 06078 Dr. Robert Hershler Division of Mollusks National Museum of Natural History Smithsonian Institution Washington, DC 20560 Dr. Richard S. Houbrick Division of Mollusks National Museum of Natural History Smithsonian Institution Washington, DC 20560 Mr. Richard I. Johnson Department of Mollusks Museum of Comparative Zoology Harvard University Cambridge, MA 02138 Dr. Aurele La Rocque Department of Geology The Ohio State University Columbus, OH 43210 Dr. James H. McLean Department of Malacology Los Angeles County Museum of Natural History 900 E.xposition Boulevard Los Angeles, CA 90007 Dr. Arthur S. Merrill % Department of Mollusks Museum of Comparative Zoology Harvard University Cambridge, MA 02138 Ms. Paula M. Mikkelsen Harbor Branch Oceanographic Institution, Inc. Ft. Pierce, FL 33450 Dr. Donald R. Moore Division of Marine Geology and Geophysics Rosenstiel School of Marine and Atmospheric Science University of Miami 4600 Rickenbacker Causeway Miami, FL 33149 Dr. Gustav Paulay Marine Laboratory University of Guam Mangilao, Guam 96923 Mr. Richard E. Petit P.O. Box 30 North Myrtle Beach, SC 29582 Dr. Edward J. Petuch Department of Geology Florida Atlantic University Boca Raton, FL 33431 Dr. David H. Stansbery Museum of Zoology The Ohio State University Columbus, OH 43210 Dr. Ruth D. Turner Department of Mollusks Museum of Comparative Zoology Harvard University Cambridge, MA 02138 Dr. Geerat J. Vermeij Department of Geology University of California at Davis Davis, CA 95616 SUBSCRIPTION INFORMATION The subscription rate per volume is US $25.00 for individuals, US $40.00 for institutions. Postage outside the United States is an additional US $5.00 for surface and US $12.00 for air mail. All orders should be accompanied b\ payment and sent to: THE NAUTILUS, P.O. Box 7279, Silver Spring, MD 20907-7279, USA. Change of address: Please inform the publisher of your new address at least 6 weeks in advance. All communications should include both old and new addresses (with zip codes) and state the effective date. THE NAUTILUS (ISSN 0028- 1344) is published quarterly by Trophon Corporation, 8911 Alton Parkway, Silver Spring, MD 20910. Second Class postage paid at Silver Spring, MD and additional maihng offices. POSTMASTER: Send address changes to: THE NAUTILUS P.O. Box 7279 Silver Spring, MD 20907-7279 THEf7NAUTILUS CONTENTS e 106, Number I Februani 27 , 1992 ISSN 0028-1344 John M. Healy !V1.G. Harasewvch Spermatogenesis in Perotrochus quoyanus (Fischer 6i Rernardi) (Gastropoda: Pleurotomariidae) 1 Riidiger Bieler Tcnagodiis of Siliquaria'-' L'rira\elini; taxonornic confusion in marine "worm-snails iCerithioidea: Sili(iuariidae) 15 Silvard P. Kool Niirclla Hodinn, 1798 ((Gastropoda: Muricidae) t\pe species 21 Kenneth J. Boss Bruce A. .Marshall A revision ot the Recent species of Eudoliuni Uall, 1889 (Gastropoda: Toiinoidea) 24 VCilliam K. Emerson James H. McLean Biiridrillia dcroijorurn. new species from the Galapagos Islands, a li\inu record of a Neogene Turrid genus 39 THE NAUTILUS 106(1):1-14, 1992 Page 1 Spermatogenesis in Perot rochus quoyanus (Fischer & Bernardi) (Gastropoda: Pleurotomariidae) John IVI. Healy Departnu'iil of Zoology The University of Queensland Si. Lueia, Brisbane Queensland, ALSTRALIA 4()H7 M.G. Harasewych Department of Invertebrate Zoology National Museum of Natural History Smithsonian Institution Washington, DC: 20560 USA ABSTRACT The male reproducti\e system, ultrastructure of spermatozoa and spermatogenesis are described for the pleurotomariid Pcr- otrochus quotjanus (Fischer i Bernardi) CIross morpholog\ of the male reproductive system of P. qtiotjanus agrees in all essential details with that of Mikadot rochus beyrichii. In all features, spermatozoa of Perotrochus quoyanm closely resem- ble those of Perotrochus westralis Whitehead, 1987, as well as spermatozoa of certain members of the Trochoidea (Trochidae, Liotiidae) Spermatozoa of P. quoyanus have a conical acro- somal vesicle with a finely ridged anterior layer, a short, rod- shaped nucleus with numerous lacunae, a midpiece consisting of five (rareK four) mitochondria surrounding a pair of cen- trioles, a rootlet cotmecting the centrioles and axonenie to the nucleus, and a flagelluni (55-58 ^m long) that is continuous with the distal centriole. Investigated species of Haliotidae and Scissurellidae {Sinezona sp.) differ from Perotrochus in acro- somal substructure, and, in the case of Sinczuna. also in mid- piece and nuclear morpholog\ Key Words. Spermatozoa, Spermatogenesis, Mollusca, Gas- tropoda, Pleurotomariidae, Perotrochus, male reproductive tract INTRODUCTION Living species of the Pleurotomariidae have a host of primitive gastropod features including a prominent la- bial shell slit as well as paired gills, auricles, osphradia, kidneys, and hypobranchial glands (Woodward, 1901; Bouvier & Fischer, 1902; Fret'ter, 1966; Hickman, 1984; Haszprunar, 1988). The Haliotidae and Scissurellidae, which share these features and classically have been as- signed to the Pleurotomarioidea, are now considered suf- ficiently different from the Pleurotomariidae to warrant their placement into separate superfamilies, while the Pleurotomarioidea is considered most closely related to the Trochoidea based on the shared presence of a glan- dular urinogenital duct in females (for discussion see Haszprunar, 1988, 1989; McLean, 1989). Basic features of pleurotomariid anatomy, including radular morphol- ogy, have been known for more than a century (Dall, 1889; Bouvier & Fischer, 1899, 1902; Pelseneer, 1899; Woodward, 1901; Fretter, 1964, 1966), but it is only in recent years that the advent of deep-sea submersible craft has allowed the biology and habitat of living specimens to be studied in detail and in situ (Yonge, 1973; Hara- sewych et ai, 1988, 1992). The field of comparative spermatology has, over the last twenty years, contributed greatly to the resolution of taxonomic and phylogenetic problems in numerous phyla (Baccetti & Afzelius, 1976; Wirth, 1984; Jamieson, 1987), including the Mollusca (Nishiwaki, 1964; Popham, 1979; Giusti, 1971; Kohnert & Storch, 1984a,b; Koike, 1985; Healy, 1983, 1986, 1988a; Hodgson et ai. 1988). Among the Gastropoda, studies of archaeogastropod (,s-./. ) spermatozoa and spermiogenesis (Kohnert & Storch, 1983; Azevedo et ai, 1985; Koike, 1985; Hodgson & Bernard, 1988; Healy, 1988b, 1989, 1990a,b) are becoming in- creasingly important since it is from this broad assem- blage that origins for the caenogastropod and euthyneu- ran groups are sought (Cox, 1960; Ponder, 1973; Haszprunar, 1988). The recent discovery of pronounced sperm dimorphism in the trochoidean Zaiipais laseroni Kershaw, 1955, including a multi-tailed, oligopyrene paraspermatozoon (Healy, 1990b), has drawn attention to the fact that comparatively little is known of the range of sperm morphologies existing in the Vetigastropoda. Healy (1988b) provided the first ultrastructural infor- mation on spermatozoa of the Pleurotomariidae [Pero- trochus westralis Whitehead, 1987,' as Plcurotomaria ajricana (Tomlin, 1948)], but, because of limitations im- posed by the state of preservation of the testes, was unable to trace e\ents of spermatogenesis or give substructural detail of certain sperm features. L'sing glutaraldehyde- fixed testicular material of Perotrochus quoijanus, we present the first ultrastructural study of sperm devel- opment in a pleurotomariid gastropod. ' For a discussion of the nomenclature of this species, see Wagner and O>onians (1990). Page 2 THE NAUTILUS, Vol. 106, No. 1 MATERIAL AND METHODS Three male specimens of the pleurotomariid Perot rochus quoyanus (Fischer & Bernardi, 1856) were collect ed us- ing the research submersible JOHNSON-SEA-LINK II, 1.03 nautical miles west of Ilets-a-Goyaves. off Basse Terre, Guadeloupe, West Indies' (16°10'33"N, 6r49'00"W) at a depth of 350-360 m. Specimens were maintained in refrigerated aquaria for six days prior to cracking the shells and excising the testes. For scanning electron microscopy (SEM), samples were prepared by teasing apart sections of fresh testes in filtered seawater, transferring droplets of sperm suspension to coverslips, and fixing with glutaraldehyde vapor (25% glutaralde- hyde in a covered petri dish). The coverslips were passed through a graded acetone series (20-100%), critical-point dried, and coated with gold-palladium. The sperm were examined using a Hitachi S-570 SEM at an accelerating voltage of 10 kv. Measurements are based on SEM pho- tographs of sperm and calibration grids of standard size (2160 lines/mm at 15,000 X for acrosomes, nuclei, and mitochondria, 19.7 lines/mm at 1,500 X for tails). For transmission electron microscopy (TEM), l-2mm^ pieces of testicular tissue were fixed with 5% glutaraldehyde in 0.2 M cacodylate buffer and shipped to the senior author. Upon arrival, samples were further fixed in cold 3% 0.2M cacodylate-buffered glutaraldehyde and washed thor- oughly in cacodylate buffer before being placed into a 1% solution of osmium tetroxide (prepared in 0.2M cac- odylate buffer) for two hours. Tissues were again rinsed in buffer, then dehydrated using an ascending series of ethanols (20-100%). Spurr s epoxy resin was used to em- bed the tissues (Spurr, 1969). Ultrathin sections were cut with an LKB IV Ultratome, collected on uncoated 200- mesh copper grids, and stained using either the double lead stain of Daddow (1983) or a single leatl procedure (20 minutes uranyl acetate, 10 minutes lead citrate). Sec- tions were examined using a Hitachi 300 transmission electron microscope operated at 75 kV. Remaining soft tissues were fixed in 10% formaldehyde in seawater and transferred to 70% ethanol for dissection. Shell fragments retained as voucher specimens are housed in the National Museum of Natural Historv, Smithsonian Institution (USNM 878154). RESULTS Male Reproductive Sy.stem The mustard-colored testis (fig. 1, te) lines the right wall of the digestive gland (fig. 1, dg) , and empties into a thin-walled testicular duct (fig. 1, td) situated ventral to both these organs. This duct becomes tubular along the ventral surface of the stomach (fig. 1, sto) and continues anteriorly, emptying (fig. 1, ga) into the ureter portion of tlie right kidney (fig. 1, u) anterior and to the right of the opening (fig. 1, o) of the anterior lobe of the right kidne\ (fig. 1, ark), which is situated in the cephalic hemocoel. The ureter/ urinogcnital duct (figs. 1. 2, u) runs anteriorly along the roof of the mantle cavity to the Sto rav rko Fipure§ 1-2. Male reproductive tract of Perotrochus qiioy- (titiis (Fischer & liernardi), I. Diagrammatic representation of male reproductive system, viewed from right side. Walls of pericardium and right kidney removed to reveal contents 2. Transverse section midway along paiiial gonoduct, viewed from anterior, ark, anterior lobe of right kidney; dg, digestive gland; ga, genital aperture; Ik, left kidney; o, opening of anterior lobe of right kidney; pc, pericardium; r, rectum; rav. right afferent liranchial vessel; rk, right kidney; rko, right kidney opening; sto, stomach; td, testicular duct; te. testis; u, urinogenilal duct. right of the rectum (figs. 1, 2, r), envelops the right afferent branchial vessel (figs. 1,2, rav), and drains into the mantle cavity through a transversely oriented right kidney opening (fig. 1, rko), approximately 1/4 of the distance from the rear of the mantle cavity to the rear of the mantle slit The urinogenital ducts of all three individuals lacked a glandular lining. The testes of two animals were full of mature sper- matozoa, while that of the third animal were almost entirely spent. .Although onl\ scattered groups of devel- oping cells remained, we were able to identif>- basic features of spermatogonia, spermatocytes and sperma- tids. Mature Testic;ular Spermatozoa (SKM observations) Spermatozoa of Perotrochus quoyanus consist of a con- ical acrosomal complex (fig. 4, a), a rod-shaped nucleus (fig 4, ii), a cluster of five, equal-sized, spherical mito- chondria (fig. 4, m, fig. 5, mp) at the base of the nucleus, and a single 55-58 ^m long Dagellum (figs. 3-4, f, table J. M. Healy and M. G. Harasewych, 1992 Page 3 Figures 3-5. Perotrochus quoyanus- Mature testicular sperm, SEM. 3. Two spermatozoa including entire Qagella (f). 4,5. Acrosome (a), nucleus (n) and mitochondria (m) of two spermatozoa. Nuclear lacuna (nl) and detached midpiece (mp) consisting of five mitochondria visible in figure 5. Scale bars: 3=10 ^m; 4,5 = 2 /um. 1). The acrosomal complex (externalK, the acrosomal vesicle proper) is approximately 1.15 ^m long, tapers slightly at contact with the nucleus, and has a maximum diameter of 1.18 //m (figs. 4,5, table 1). The nucleus measures 3.7 ^m in length, is broadest posteriorly, with a maximum diameter of 1.4 nm. Irregular indentations on the nuclear surface (Bg. 5, nl) can be correlated by TEM with nuclear lacunae (figs. 6, 7, 11, nl) occurring beneath the nuclear and plasma membranes. These in- dentations are not, therefore, nuclear pores. Spherical mitochondria (diameter 0.8 /im) obscure the attachment site of the Dagellum. The flagellum narrows markedly towards its insertion point within the midpiece (figs. 13,15). Mature Testicular Spermatozoa (TEM observations) Acrosome: The acrosomal vesicle is broadly conical, with a rounded anterior surface and flattened basal sur- face (fig. 7, av). The vesicle has a length of 0.90-0.93 nm and the maximum diameter of 1.28 ixm at its base is wider than the apex of the nucleus (figs. 7,8, n). A deep, narrow invagination extends anteriorly from the base of the vesicle and is filled with a diffuse, faintly fibrous material (figs. 8, 10, sm). Some sections clearly indicate an eccentric, slightly angular alignment for the invagination relative to the sperm longitudinal axis (figs. 8, 10). Beneath the anterior face of the acrosomal vesicle is an electron-lucent layer containing fine ridges with a periodicity of 12-14nm (figs. 7,9, rl). A similarly electron- lucent layer, lacking discernible ridged substructure, forms the basal rim of the acrosomal vesicle (fig. 7, br). A loose, fibrous deposit of subacrosomal material occupies the space between the base of the acrosomal vesicle and the nuclear apex (fig. 8, sm). Nucleus: The mature nucleus (fig. 6, n) is short (3.7 ^m) and almost cylindrical, with a shallow depression ante- riorly (figs. 7, 8, n) and five (rarely four) shallow de- pressions surrounding a centriolar fossa posteriorly (figs. 14, 15, n). The anterior depression is associated with subacrosomal material (fig. 8, sm), while the posterior depressions act as sockets for the midpiece mitochondria (fig. 15, m). Dense material linking the proximal and Page 4 THE NAUTILUS, Vol. 106, No. 1 Table 1. Dimensions of mature spermatozoa from SEM ob- servations. Linear measurements in fin\. (n = .30, 10 sperm from each of three individuals.) Standard deviation Mean Range (<7) Acrosome Length Lie 1.01-1.19 0.07 Width LOS 1.01-1.18 0.05 Nucleus Length 3.67 3.52-3.78 0.08 Width (anterior) 0.98 0.95-1.03 0.02 Width (posterior) L19 1.13-1.34 0.08 Mitochondria Diameter 0.80 0.68-0.93 0.09 Flagellum Length 56,5 .52.7-61.1 3.26 distal centrioles is continuous with a hollow rootlet (figs. 14, 15, r), the bulbous end of which fills the centriolar fossa. Numerous irregularly shaped lacunae (figs. 6, 7, 11, nl) occur within the nucleus, some of which open underneath the nuclear membranes, though not to the plasma membrane or cell surface. Nuclear contents are highly electron dense and consist of tightly packed fibers (diameter 16 nm) set in a finely granular matrix. Midpiece: Five (rarely four) spherical (diameter 0.6- 0.8 ^m) mitochondria (figs. 12, 15, m), each having curved, plate-like cristae, surround the proximal and dis- tal centrioles to form the sperm midpiece (fig. 12). The centrioles (figs. 14, 15, pc, dc), arranged at a 90° angle to each other, are hollow, cylindrical structures composed of triplet microtubules and emliedded in a pericentriolar matrix (triplets often obscured by matrix, see fig. 15 inset). Nine satellite fibers (figs. 15, 16, sf) connect the distal centriole to an annulus (figs. 15,16, an), a ring- shaped deposit of material lining the inner surface of the plasma membrane. The flagellar axoneme, therefore, is anchored to the midpiece and nucleus via the centrioles and rootlet as well as by the radial set of satellite fibers. Flagellum: The flagellum measures approximately 55- 58 yuni ill length and consists of a 9 + 2 axoneme enclosed by the plasma membrane (figs. 15, f; 17). Many sper- matozoa were observed with an angularly offset flagellar- centriolar apparatus (fig. 13). This misalignment could be due to tight packing of sperm within the testis or even slight immaturity, since our .SEM observations on free sperm show a normal, posteriorly projecting flagellum (figs. 3-5). Occasionally, a dense body is enclosed with the axoneme by the plasma membrane (fig. 17, db). Its position along the flagellum could not be determined. Further study is required to determine whether this structure is a true sperm feature of P. quoyanus or an artifact of fixation. In the distal region of the flagellum, the 9 + 2 substructure of the axoneme degenerates into singlet microtubules (fig. 17, arrow). Spermatogenesis Spermatogenic cells present within the testis consisted principally of isolated clumps of spermatocytes and sper- matids (fig. 18, spc, spt). Most of the testis space in ripe males was found to be almost totally occupied by tightly packed mature spermatozoa. To some extent the process of reconstructing events of spermatogenesis was ham- pered by the occurrence of many abnormally developing spermatocytes and spermatids. The morphology and pos- sible significance of these cells is treated in the final section of these results. Spermatogonia: Spermatogonia (fig. 19) were only rare- ly observed. They can be distinguished from spermato- cytes and spermatids by their oblong, usualK lobulate nucleus (fig. 19, n; length 6.0 ^m, breadth 4.0 /um), prom- inent nucleolus (fig. 19, nc; diameter 0.7 nm), well-de- veloped nuclear pores (fig. 19, arrows), numerous small mitochondria (fig. 19, m; diameter 0.3-0.4 ^m), and more extensive cytoplasm. Endoplasmic reticular cisternae, where visible, are scattered and poorly developed. The presence of centrioles and Golgi complex could not be confirmed in the limited number of observed cells. Spermatocytes: Spermatocytes (fig. 20) have a spherical to ovoid nucleus (fig. 20, n; diameter 4.0-4.5 ^m) that appears to lack either a nucleolus or prominent nuclear pores. The small electron-dense patches visible in many cells (fig. 20, arrowheads) ma\ be sites of s\naptinemal complexes, although these structures are more easily dis- cerned in moribund spermatocytes that have partially lost nuclear contents (fig. 38, arrows). Mitochondria (fig. 20, m; diameter 0.6-0.75 jum) markedK larger than those of spermatogonia are pressed slightK into the surface of the nucleus. Highly electron-dense proacrosomal vesicles (fig. 20, pav; diameter 0.1-0.2 ^l^\) of Golgian origin are foimd throughout the cytoplasm. The axoneme (fig. 21, ax) de\elops intracellularly from one of a pair of or- thogonally arranged centrioles (fig. 21, pc, dc) positioned close to the concave face of the Golgi complex (fig. 21, G). Even at this early stage in axoneme formation, sat- ellite fibers (fig. 21, sf) are associated with the future Figures 6-17. Perotrochus quoyanus. Mature testicular sperm, TEM 6. Acrosome (a), nucleus (n), nuclear lacunae (nl), and mitochondria (m) of two spermatozoa. 7,8. Acrosomal vesicle (av) showing ridged layer (rl), basal rim (br), subacrosomal material (sm), and apex of nucleus (n) with nuclear lacuna (nl). 9. Detail of ridged laser (rl) in acrosome 10. Transverse section throng!) acrosomal vesicle showing subacrosomal material (sin). I 1. Transverse section through nucleus showing nuclear lacuna (nl). 12. Transverse section ihrougli midpiece, five mitochondria (m) surround the distal centriole (dc) 1.3. ,\ngularl\ offset centriolar (c) — flagellum (f) apparatus of a spermatozoon. 14. Detail of centriolar fossa and attached rootJcl \r), proximal (pc) and di.stal centrioles •^i -^ 15 (dc), and mitochondria (m), 15. Base of nucleus (n), rootlet (r), proximal (pc) and distal (dc) centrioles, satellite fibers (sf ), annulus (an), flagelluni (f), and mitochondria (m). Inset: triplet microtubules of proximal centriole (arrowheads). 16. Oblique section showing distal centriole and three of nine satellite fibers (sf) attached to annulus (an). 17. Transverse section through flagella. Note distal region (right) and dense bod> (db) (left). .Arrow indicates singlet microtubules in distal region of flagelluni. Scale bars: 6 = 1 Mm; 7,8,10-17 = 0.25 mi"; 9 = 0. 1 m'". Page 6 THE NAUTILUS, Vol. 106, No. 1 distal centriole. Endoplasmic reticular cisternae are poor- ly developed. Spermatids (Speriiiiogenesis): Spermatids can be di- vided into three categories based on the condensed state of the nucleus: early cells, middle-stage cells, and ad- vanced spermatids. In early spermatids the nucleus (fig. 22, n) is spherical with pale-staining, fibrous contents. Middle-stage sper- matids (figs. 23,24) are distinguished from earlier cells liy a marked increase in the electron densit\ of the nu- clear fibers, and by a tendency of the mitochondria and centrioles to move toward the incipient posterior pole of the nucleus. Although multiple proacrosomal vesicles are still apparent within the c\ toplasm of middle-stage sper- matids (figs. 24, 25, pav), it is during this phase of sper- miogenesis that the definitive acrosomal vesicle is formed by fusion of proacrosomal vesicles. In advanced sper- matids, mitochondria and the acrosomal vesicle come to lie in shallow depressions of the nucleus, while the nu- cleus itself becomes oblong and its constituent fibers more condensed (figs. 26,27,36,37). In addition, the acrosomal vesicle undergoes pronounced changes in shape and sub- structure. Initially, the acrosomal vesicle is round and underlain by a thin disjointed layer of subacrosomal ma- terial (fig. 26, sm). As seen in figure 26, the site of first contact between the definitive acrosomal vesicle and nu- cleus may occur close to where the mitochondria are situated. Following attachment of the acrosomal vesicle to the condensing nucleus, vesicle contents become dif- ferentiated into a cluster of coarse granules (fig. 27, g) and a more extensive homogeneous portion (fig. 27, h). These granules become partitioned into two deposits that occupy anterior and posterior depressions in the homo- geneous portion (fig. 28). Subsequently, an invagination of the homogeneous portion, but not the acrosomal mem- brane, begins to form anteriorly (fig. 29, arrowhead). The anterior cluster of granules transforms into a finely ridged layer (figs. 28-34, rl). As this layer grows, it ex- tends into a deepening invagination of the homogeneous portion (figs. 29-31, arrowhead). The posterior cluster of granules forms the electron-lucent basal rim of the ac- rosomal vesicle. A thin deposit of dense material defines the basal region of the acrosomal membrane (figs. 28,29, dm). Late in spermiogenesis, the basal invagination of the acrosomal vesicle develops and is filled with suba- crosomal material (fig. 31, sm). The anterior invagination of the homogeneous portion, which is not an invagination of the vesicle membrane, and the basal invagination of the vesicle are distinct and unconnected structures. The anterior invagination ultimately disappears, perhaps by a process of eversion, leaving the ridged electron-lucent layer (figs. 31,34,35, rl) and a small electron-lucent i)late (figs. 31,34,35, asterisk). Nuclear lacunae, so clearly apparent in mature testic- ular spermatozoa, only become evident in the very last stage of spermiogenesis. These spaces are not in contact with the exterior of the spermatid. The ccntriolar fo.ssa (fig. 36, arrowhead) forms through invagination ol the nuclear extension that lies between the posteriorly po- sitioned mitochondria Origins of the pericentriolar ma- trix and centriolar rootlet were not determined. Presum- ably the centrioles play some role in the growth of these structures. Aberrant spermiogenic cells: In addition to spermat- ogonia, spermatocytes and spermatids, the testes also con- tained numerous abnormally developing spermatocytes and spermatids. Some of these spermatocytes appear moribund (fig. 38). The spermatids, however, are clearly recognizable by their angular shape, evidently the result of cytoplasmic pressure from adjacent cells (figs. 18, spt; 39). Nuclear condensation and proacrosomal vesicle pro- duction seem to proceed as in normally developing cells. Gradually, however, the nucleus becomes oblong then angular and ultimately irregular in shape (figs. 39-42). Like normal spermatozoa, mature nuclei of the abnor- mal, presumably abortive, lines have numerous lacunae (fig. 42, nl) and a fibro-granulate substructure (figs. 40- 42). The proacrosomal vesicles, rather than forming a definitive acrosomal vesicle, remain as a clump of un- fused entities (Figure 40, inset, pav). Mitochondria, lo- cated in depressions of the nucleus, and axonemal profiles are often observed in developing and mature aberrant spermatozoa (figs. 40, m; 41, ax). The position and num- ber of centrioles was not determined. DISCUSSION Reproductive System: The morphology of the male re- productive system of Perotrochus quoyanus agrees in all major features with that of Mikadotrochus bcyrichii. the only other species of pleurotomariid for which the male reproductive system has been documented (Woodward, 1901). The female reproductive system of pleurotoma- riids differs from the male reproductive s\stem in that the pallial portion of the right kidney, the urinogenital duct, is glandular. To date, only M. beyrichii (Wood- ward, 1901) and Perotrochus midas (Fretter, 1966) are confirmed to have glandular female urinogenital ducts. The duct of the holot\ pe of Perotrochus amabilis (Bayer, 1963), an "immature' female on the basis of gonadal sections, lacked glandular elements, prompting Fretter (1964:179) to suggest that this was a young individual that had never spawned, and that glands may develop in the walls of this duct only as the gonad becomes mature. Examination of the shells of more than a dozen specimens collected in the intervening decades reveals that the holotype of M. arnahilis is among the larger specimens known of this species. It is therefore unlikely that the holotype is an immature individual. Gonadal development of several western Atlantic pleurotomariids varies with season (Harasewych, unpublished observa- tions), suggestitig that the glandular lining of the uri- nogenital duct of females may develop and diminish cyclically. As evidenced by the three specimens used in this stud) , the urinogenital ducts of male pleurotomariids arc not glandular, even during the spawning season. Nev- ertheless, absence of a glandular urinogenital duct may 18 •*•• 19 • /' s^^ 'M Figure§ 18-24. I'crotrvchus qiioyanus. Spermatogenesis, 18. Survey section of testis showing spermatozoa (spz), developing spermatocytes (spc), and advanced spermatids (spt). Arrows indicate aberrant spermatids. 19. Spermatogonium, Note lobulate nucleus (n), large nucleolus (nc), nuclear pores (arrows), and numerous small mitochondria (m), 20. Spermatocytes. Note mito- chondria (m), nucleus (n), presence of proacrosomal vesicles (pav), and putative synaptinemal complexes (arrowheads). 21. Sper- matocyte Golgi complex (G) close to proximal and distal centrioles (pc, dc) and axoneme (ax). Note satellite fibres (sf) associated with distal centriole. 22. Early spermatids (spt) with homogeneously granular nuclei (n) and proacrosomal vesicles (pav). 23. Middle stage spermatids with very electron dense fibrillar nuclei (n) and mitochondria (m). 24. Middle stage spermatid showing pair of centrioles (c), proacrosomal vesicles (pav), and mitochondria (m). Scale bars: 18 = 10 ^m; 19,20.22-24 = 1 Mm; 21 = 0.5 Mm. Pages THE NAUTILUS, Vol. 106, No. 1 y. a; FiguiT., 2.> .>.i (.;. Ini:. quuy.iiui.; \k icwiiiif (Ifvelupmeiil. 25. (iruup of proacTo.sonial vesicles (pav) near mitochondrion (m) and axoneme (ax). 26. Spermatid with acrosomal vesicle (av) contacting nucleus (n) near mitochondrion (m) Subacrosomal J. M. Heal) and M. G. Harasewych. 1992 Page 9 not be a sufficient criterion for identifying male speci- mens. Spermatogenesis: Despite the complicating factor of moribund and abnormally developing cells within the testis, spermatogenic stages of Perotrochus quoyanus re- semble those reported for the Trochoidea (Kohnert & Storch, 1983; Azevedo et a/., 19S5; Koike, 1985; Healy, 1989). Using museum-preserved tissues, Healy (1988b) was able to determine that acrosomal development in Perotrochus westralis involved the production of mul- tiple proacrosomal vesicles. Fusion of proacrosomal ves- icles into a definitive acrosomal vesicle has been dem- onstrated in many bivalves (Longo & Dornfeld, 1967; Kubo, 1977; Bernard & Hodgson, 1985; Hodgson & Ber- nard, 1986; Eckelbarger et ai, 1990), and, outside the Mollusca, in groups as disparate as the Polychaeta (Fran- zen, 1987) and Echinodermata (Dan & Sirakami, 1971; Chia & Bickell, 1983). In contrast, acrosome develop- ment in patelloidean gastropods centers on the produc- tion of a single, electron-lucent vesicle to which small vesicles from the Golgi cisternal edges fuse and contrib- ute (Hodgson & Bernard, 1988). Our study has discov- ered details of acrosome development previously unde- scribed in the Vetigastropoda, including the differentiation of anterior and posterior extremities of the vesicle and formation of fine ridges in the anterior electron-lucent layer. There are reasons for believing that these events also occur in the Trochoidea. Mature ac- rosomes of trochids frequently show anterior and pos- terior electron-lucent layers (the anterior layer with ridg- es: HeaK & Daddow unpublished). In spermatids of Omphalius pfeifferi (Philippi, 1846), the definitive ac- rosomal vesicle (Koike, 1985:plate 3D) closely corre- sponds to the stage illustrated herein for Perotrochus quoyanus (fig. 30). The origin of the subacrosomal ma- terial in P. quoyanus and in Giblntla umbilicalis (da Costa, 1778) (see Azevedo et ai, 1985) is unknown. A Golgian source seems unlikely, as this secretory organelle has migrated posteriorly by the time the definitive ac- rosomal vesicle has formed (the stage when subacrosomal material becomes visible). Possibly, the acrosomal vesicle itself is capable of organizing the accretion or polymer- ization of extravesicular materials within the cytoplasm. Takaichi & Dan (1977) proposed a similar origin for subacrosomal material in the pulmonate Euhadra hick- onis (Kobelt, 1879). An interesting feature of spermio- genesis in Perotrochus quoyanus is the often distant po- sitioning of the nuclear-contacted acrosomal vesicle relative to this vesicle's final position at the nuclear apex (see fig. 26). A comparable situation occurs in the trochid Calliotropis glyptus (Watson, 1879) (see Healy, 1989) and evidently in the turbinid Lunella granulata (Gmelin, 1791) (see micrographs of Koike, 1985). In Perotrochus, Calliotropis, and Lunella, however, the mature acro- .somal vesicle lies at the nuclear apex, indicating that by some means, perhaps via nuclear shape change late in spermiogenesis or acrosomal movement, the vesicle at- tains its final position. The pattern of nuclear condensation in Perotrochus quoyanus differs from that occurring in the Trochoidea in two respects: (1) the heterochromatin forms a ho- mogeneous network of dense fibers, whereas the hetero- chromatin forms distinct granules in Trochoidea; and (2) nuclear lacunae appear only at the last stage of spermatid development, whereas the lacunae are well developed and visible at earlier stages in Trochoidea (Kohnert & Storch, 1983; Azevedo et a!., 1985; Koike, 1985; Healy, unpublished data). Unfortunately, no comparative in- formation exists on nuclear condensation or, in fact, on any aspect of spermiogenesis, in the Haliotidoidea, Scis- surelloidea, or Fissurelloidea. Initially thecentriolar fossa of Calliotropis glyptus spermatids resemble the mature fossa of Perotrochus spp., but late in spermiogenesis, the solid rootlet and attached centrioles of C. glyptus become drawn into a greatly expanded fossa (Healy, 1989). Incorporation of the future flagellar axoneme within the cytoplasm of spermatocytes and spermatids in Per- otrochus warrants some comment. The same phenom- enon can be seen in published micrographs of developing spermatids in the trochid Monodonta turbinata (Born, 1778) (see Kohnert & Storch, 1983) and in the turbinid Lunella granulata (see Koike, 1985). Unfortunately, nei- ther Kohnert and Storch (1983) nor Koike (1985) offer a discussion of this positioning of the axoneme. In sper- matids of the caudofoveate Chaetoderma sp., the prox- imal and distal centrioles each give rise to an axoneme within the cytoplasm (Buckland-Nicks & Chia, 1989). Of these two axonemes, only that associated with the future distal centriole survives into the mature sperma- tozoon. A similar situation has been reported by Eckel- barger et al. (1989) in paraspermatozoan development of the abyssal sea urchin Phrissocijstis multispina, with the exception that both axonemes survive in the mature cell. Given the large number of abnormally developing spermatids observed in the ripe testes of our specimens of Perotrochus quoyanus, it cannot be ruled out that the intracellular axoneme in spermatids of this species may material (sin) is thin. Arrowheads indicate axonemal profiles. 27. Acrosomal vesicle showing granule cluster (g) and homogeneous portion (h) of vesicle contents. Note also subacrosomal material (sm ), 28. Granules (g) distributed in anterior and posterior depressions of homogeneous portion (h). Note ridged layer (rl) and basal rim defined by dense material (dm). 29. Beginning of invagination (arrowhead) of homogeneous portion (h). 30. Penetration of ridged layer (rl) into deepening invagination (arrowhead) of homo- geneous portion. 3 1 . Acrosome of late spermatid showing developing basal invagination of acrosomal vesicle as well as invagination of homogeneous portion (arrowhead). Asterisk indicates electron-lucent plate 32-34. Sequence of ridged layer (rl) development shown in detail Granule cluster (g). .'Vsterisk indicates electron-lucent plate. 35. Nearly mature acrosome. Electron-lucent plate indicated h\ asterisk. Subacrosomal material (sm). Scale bars: 25,26 = 0.5 nm. 27-35 = 0.25 ^m. Page 10 THE NAUTILUS, Vol. 106, No. 1 be an aberrant rather tlian normal feature. Examination of testes from animals collected at the commencement of the reproductive season should resolve this question. Aberrations in spermatogenesis: Few ultrastructural studies have dealt w itli the incidence of spermatogenic abnormalities in niollusks. Takaichi (1979) detailed ra- diation-induced malformations of the mitochondrial sheath and nucleus and duplication of the axoneme in spermatids of the pulmonale Euhadra hickonis. Dorange and Le Peiinec (1989) noted binuclear spermatids and angularly dislocated axonemes in late spermatids of Pec- ten maximus (Linne, 1758) and regarded these features as true aberrancies. O'Foighil (1985) suggested that an- gular dislocation of the axoneme in testicular sperm of the bivalve Lasaea suhviridU Dall, 1899 could be due to slight immaturity. In Perotrochus quoyanus we have observed numerous spermatocytes and spermatids that were undergoing a form of development clearly different from normal spermatogenesis. Leaving aside the phe- nomenon of sperm dimorphism (a well-documented and 'normal' occurrence in many Caenogastropoda — see Healy, 1988a for discussion), the irregular shape of the condensed nucleus (pressed into shape by abutting cells), and the apparent inability of proacrosomal vesicles to fuse into a single acrosomal vesicle, strongly suggest that these are abnormal cells. Bearing in mind that a certain background level of spermatogenic abnormality proba- bly exists in many if not most animal species (Bryan & Wolosewick,1973; Baccetti & Afzelius, 1976), we believe the appearance of aberrant cells in P. quoyanus is prob- ably a normal event heralding the end of the annual reproductive phase in this species. We base this view on the fact that all three males examined were either spent or contained principally mature spermatozoa in the testis (with isolated pockets of developing and aljnormal sper- matogenic stages). Spermatozoa: Healy (1988b) has previously drawn at- tention to the structural similarities between spermatozoa of Perotrochus westralis and those of the Trochoidea, particularly Trochidae. Our observations on glutaral- dehyde-fixed testis sperm of P. quoyanus have enabled us not only to confirm these similarities but also to expand on details of the Perotrochus spermatozoon as recon- structed by Healy from sea-water formalin/ethanol-pre- served material. The electron-lucent anterior layer of the Perotrochus acro-somal vesicle contains regularly spaced ridges. Sim- ilar ridges have elsewhere been observed in the Trochi- dae [A!/.s7ro('Of/j/ra roni^ric^a (Lamarck, 1822), Banhivia australis (Menke, 1830); Healy & Daddow unpublished] and in the liotiid Liotina peronii (Kiener, 1839) (Healy & Ponder unpublished). It is interesting to note that the acrosomal vesicle of other pleurotomarioidean (s./.) fam- ilies (Haliotis spp. — Haliotidae, Lewis et al., 1980; Sakai et al., 1982; Sinezona sp. — Scissurellidae, Healy, 1990a) lack an electron-lucent anterior layer, whereas in the fissurellids Scutiis antipodes Montfort, 1810 and Mont- fortuhi conoidea Reeve, 1842, a layer is present but exhibits no discernible ridged substructure (Healy, un- published). The acrosomal complex in Haliotis and in Sinezona also differs from that of Perotrochus b\ having an extensive subacrosomal deposit similar to that seen in spermatozoa of some fissurellids (Scutus antipodes, Montforttila conoidea — see Healy, 1990a for illustra- tions) and many bivalve species (see references in Po- pham, 1979). The difference in appearance of subacro- somal material between Perotrochus westralis (rod-like) and P. quoyanus (diffuse, with some evidence of fibrous texture), may be due to use of different fixation methods (P. westralis — sea water formalin/ethanol; P. quoyan- us— glutaraldehyde in cacodylate buffer). Azevedo et al. (1985) state that exposure of spermatozoa of Gibbula unihilicalis to sea water for five minutes resulted in a clearly defined rod (or perforatorium), deri\ed from a formerly diffuse subacrosomal substance. It therefore seems possible that the subacrosomal rod of P. westralis may also be an end product of prolonged exposure to sea water. The dense layer of material visible within the subacrosomal material in the vicinity of the nuclear apex (see figs. 7, 8) may also be involved in rod formation. This layer was observed by Healy (1988b) in sea water- formalin/ethanol fixed sperm of P. westralis and inter- preted as the possible remnants of nuclear membranes. Our observations, based on glutaraldehyde-fixed sperm ot P. quoyanus, show that such material truly lies outside the intact nuclear and acrosomal membranes, and there- fore constitutes part of the subacrosomal material. The close resemblance of the crypt-like nuclear fossa of Perotrochus spp. (HeaK, 198Sb; this study) to the spermatid fossa of Calliotropis glyptus (Healy, 1989) has already been mentioned. In most vetigastropods and the Patellogastropoda, the centrioles are only superficially attached to a shallow nuclear invagination. In Haliotis, the proximal centriole itself sometimes occupies the shal- low fossa (Lewis et al, 1980; Sakai et al.. 1982), while in Sinezona (Scissurellidae) and Calliotropis (Trochidae) the centriole(s) and proximal portion of the a.xoneme are Figures 36-42. Perotrochus quoyanus '.ib.'.M. IJcvt'lopiiig iiucleu.s (n), iiiidpiece niitoclidndria (m). axoneme (ax), centrioiar fossa (arrowhead), and proxiiiiu! (pel and (iLslai (("iitrioies ulc) of advanced spermatids. 36 Inset. Triplet microtubules of centriole in advanced spermatid 38. Morihund spermatoc\te sliowing s\ iiaptinemal complex (arrows), mitocliondria (m). proacrosomal vesicles (pav), and axoneme profiles (arrowheads). 3'>. .\herrant spermatit! Note angular shape of cell and its condensing nucleus (n), as well as the presence ot proacrosomal vesicles and milocliondria (m) M). Mature' aberrant spermatozoon wedged between early, prohabb normal spermatids. Note mitociiondria (ni) in depressions al base of nucleus (n) Inset. Detail of unfused proacrosomal vesicles (pav) from aberrant spermatozoon. 41. Fully "condensed' nucleus (n) of aberrant spcini showing irregular shape and multiple axonemal profiles (ax). 42. Nuclear lacunae (nl) of aberrant spermatozoon Scale bars: 36,37,40 Inset,4l,42 = 0.25 tim. 38-40 = 1 m"i J. M. Healy and M. G. Harasewych, 1992 Page 11 Page 12 THE NAUTILUS, Vol 106, No. 1 actually contained within the fossa (Healy, 1989, 1990a). The ball-and-socket fitting of rootlet and centriolar fossa of Perot rochtis spp. is unusual among gastropods, al- though a similar configuration occurs in the shipworm bivalve Lyrodus bipartita (Jeffreys, 1860) (see Figure 4 of Popham, 1974). Examination of other genera {Mi- kadotrochtts. Entemnotrochus) may show this type of nuclear fossa to be a feature of all Pleurotomariidae. Nuclear lacunae are widely reported in spermatozoa of externally fertilizing mollusks, polychaetes, brachio- pods, echinoderms, as well as of some internally fertil- izing groups (e.g. some teleosts, Homo) (Baccetti & Afzel- ius, 1976). Their occurrence or degree of development seems to be more closely linked with the mode of nuclear condensation than with the degree of modification of nuclear shape occurring during spermiogenesis. For ex- ample, in the trochoid Zaiipais lascroni. the euspermatid nucleus undergoes marked elongation during conden- sation (fibro-granular pattern), but retains lacunae that ultimately fuse to form an axial tube within the mature, filiform nucleus (Healy, 1990b). Lacunae are usually not observed where nuclear condensation proceeds through either or both longitudinal fibrillar and lamellar phases (see Kaye, 1969; Horstman, 1970, Maxwell, 1983; Koh- nert & Storch, 1984b; Koike, 1985). The midpiece and satellite fiber/centriole complex of Perotrochus spp. are essentially as observed in the ma- jority of Vetigastropoda and Patelloidea (Koike, 1985; Hodgson & Bernard, 1988; Healy, 1990a; Healy & Dad- dow unpublished), the Bivalvia (for references see Po- pham, 1979), Scaphopoda (Dufresne-Dube et al, 1983) and Caudofoveata (Buckland-Nicks & Chia, 1989). The same arrangement of these organelles, clearly one asso- ciated with sperm tail attachment and stability, also oc- curs in spermatozoa of many other externally fertilizing animal species (for major references see Baccetti & Afzel- ius, 1976; Wirth, 1984). The flagellum consists of an axoneme (9 + 2 microtu- bular substructure) sheathed by the plasma membrane. Our scanning electron micrographs reveal that the fla- gellum is narrower in diameter close to the nucleus. TEM observations suggest that this is probably the result of a more closely applied plasma membrane in this region of the flagellum, although slight narrowing of the axoneme does occur near the distal centriole (see figs. 4, 15). At present we caruiot clarify the origin of the dense body .sometimes observed within the flagellum (see fig. 17). It was not observed in longitudinal sections through the immediate post-nuclear region of the flagellum and could yet prove to be an artifact of fixation. Systematic Considerations: If spermatozoa of Perotro- chus spp. are representative of the Pleurotomariidae, then a closer relationship between this family and the Trochoidea (particularly Trochidae) than with the other pleurotomarioidean {s.l.) families Haliotidae and Scis- surellidae seems evident. This conclusion accords both with Ilas/.prunar's (1988, 1989) finding that no synapo- morphies exist to unite the Pleurotomarioidea (s.l.), and with his decision to place the Haliotidae and Scissurel- lidae into separate superfamilies within the Vetigastro- poda. The question as to whether ancestral vetigastropods were more like scissurellids than pleurotomariids (see Haszprunar, 1988, 1989 for discussion) cannot yet be resolved using sperm data alone because too many sig- nificant taxa (including the new hydrothermal vent groups) remain unstudied. Based on the present evi- dence, however, we suspect that spermatozoa of any stem vetigastropod would have resembled more closely the unmodified type of Perotrochus (Healy, 1988b; this pa- per) than the modified type of Sinezona (Healy, 1990a). Vetigastropoda, Patellogastropoda and Neritimorpha can be distinguished on the basis of sperm features (es- pecially acrosomal and nuclear) and features of sper- miogenesis (dimorphic in the case of the Neritimorpha; rarely so in the Vetigastropoda) (Koike, 1985; Healy, 1988a, 1990a, b). It will be interesting to determine whether the cocculinids — once included in the Vetigas- tropoda (Salvini-Plawen, 1980) but since removed to a separate archaeogastropod suborder, Cocculiniformia (Salvini-Plawen & Haszprunar, 1987) — also show char- acteristic sperm and spermiogenic features. ACKNOWLEDGMENTS We are grateful to the crews of the Johnson-Sea- Link II submersible and the R/V Seward Johnson for their assistance in collecting and maintaining the specimens upon which this study is based. Thanks are are extended to Professor G. Grigg of the Department of Zoology, University of Queensland for providing access to TEM facilities and to Mrs. L. Daddow and Mr. T. Gorringe (also Department of Zoology) for assistance with TEM and photography. Financial support for the work has been provided by a Queensland Museum Postdoctoral Research Fellowship (to J.M.H.). This study represents contribution number 284 of the Smithsonian Marine Sta- tion at Link Port, and contribution number 881 of the Harbor Branch Oceanographic Institution. LITERATURE CITED Azevedo, C, A. Lobo-Da-Cunha, and E. Oliveira 198.5 Ul- trastructure of the spermatozoon in Gibbula umbilicalis (Gastropoda, Prosobranchia), with special reference to ac- rosomal formation. 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Woodward, M F. 1901 The anatomy of PIciirotornaria beyr- ichi Hilg. Quarterly Journal of Microscopical Science 44(2): 21.5-268. Y'onge, C. M. 1973. Observation of the pleurotomariid En- temnotrochus adansoniana in its natural haliitat. Nature 241(5.384):66-68. THE NAUTILUS 106(l):15-20, 1992 Page 15 Tenagodus or Siliqiiaria? Unraveling Taxonomic Confusion in Marine "Worm-Snails" (Cerithioidea: Siliquariidae) Riidiger Bieler Department of Zoology Field Museum of Natural History Roosevelt Road at Lake Shore Drive Chicago, IL 60605, L'SA ABSTRACT The nomenclatural history and availability of some genus- and family-group names in the marine "worm-snair' family Sili- quariidae are discussed: (1) Tenagodus Guettard, 1770 (type species; Serpula anguina Linne, 17.5iS) has priority over its objective junior synon\m Siliqiiaria Bruguiere, 1789. Tena- godes. Tenagoda and Silicaria are unjustified emendations Siliqiiaria Schumacher, 1817 (also subsequently emended to Silicaria) is a junior homonym described in the Bivalvia. (2) Siliquarius Montfort. 1810 (type species: Siliqitarim angiiiliis Montfort, 1810) is an available name. (3) Angiiinaria Schu- macher, 1817, is preoccupied by Angninaria Lamarck, 1816 (Bryozoa). (4) Montfortia Delia Campana, 1890 (non Mont- forlia Recluz, 1843), and its replacement name Hcmitcnago- diis Rovereto, 1899, are based on the type species Tenagodus bernardii Morch, 1860. (.5) Agaihirscs Montfort, 1808, is based, b\ original designation, on (he t\pe species .A^af/ilr,sc.s/iir('<'//i(.s Montfort, 1808 (a senior synon\ni of Siliqiiaria spinosa La- marck, 1818). Agathyrsus Herrmannsen, 1846, is an unjustified emendation; "Agathinus," "Agathirsis" and 'Agathirsus ' are incorrect subsequent spellings. (6) The family name Siliquarii- dae Anton, 1838, has priority over its objective junior synonym Tenagodidae Gill, 1871 Key uords: Ta\