A Review of Morphological Characters of Hydrobioid Snails ROBERT H ERSHLER and WINSTON F. PONDER Ifc SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 600 SERIES PUBLICATIONS OF THE SMITHSONIAN INSTITUTION Emphasis upon publication as a means of "diffusing knowledge" was expressed by the first Secretary of the Smithsonian. In his formal plan for the Institution, Joseph Henry outlined a program that included the following statement: "It is proposed to publish a series of reports, giving an account of the new discoveries in science, and of the changes made from year to year in all branches of knowledge." This theme of basic research has been adhered to through the years by thousands of titles issued in series publications under the Smithsonian imprint, commencing with Smithsonian Contributions to Knowledge in 1848 and continuing with the following active series: Smithsonian Contributions to Anthropology Smithsonian Contributions to Astrophysics Smithsonian Contributions to Botany Smithsonian Contributions to the Earth Sciences Smithsonian Contributions to the Marine Sciences Smithsonian Contributions to Paleobiology Smithsonian Contributions to Zoology Smithsonian Folklife Studies Smithsonian Studies in Air and Space Smithsonian Studies in History and Technology In these series, the Institution publishes small papers and full-scale monographs that report the research and collections of its various museums and bureaux or of professional colleagues in the world of science and scholarship. The publications are distributed by mailing lists to libraries, universities, and similar institutions throughout the world. Papers or monographs submitted for series publication are received by the Smithsonian Institution Press, subject to its own review for format and style, only through departments of the various Smithsonian museums or bureaux, where the manuscripts are given substantive review. Press requirements for manuscript and art preparation are outlined on the inside back cover. Robert McC. Adams Secretary Smithsonian Institution SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 600 A Review of Morphological Characters of Hydrobioid Snails Robert Hershler and Winston F. Ponder ISSUED JUL 101996 SMITHSONIAN INSTITUTION SMITHSONIAN INSTITUTION PRESS Washington, D.C. 1998 ABSTRACT Hershler, Robert, and Winston F. Ponder. A Review of Morphological Characters of Hydrobioid Snails. Smithsonian Contributions to Zoology, number 600, 55 pages, 21 figures, 1998.—We provide herein a description of morphological characters of aquatic gastropods of the family Hydrobiidae and of several other families of Rissooidea that resemble these snails in general features. The hydrobiid gastropods comprise the largest group of freshwater mollusks, with more than 1,000 species and more than 400 Recent and fossil genera. This compilation is a prelude to the first rigorous phylogenetic analysis of the higher taxa of this cosmopolitan, yet poorly understood, group, for which at least 70 family-group taxa have been proposed. It also was prepared to fulfill a need for standardization of terminology and interpretation of characters used in taxonomic descriptions of these small, often morphologically simple, snails. Given that taxonomic study of these animals has long been hampered by reliance on a limited number of morphological features, all aspects of the shell and the soft-part anatomy are reviewed as part of this treatment, and we attempt to be maximally inclusive in listing characters. Emphasis is placed on characters considered potentially useful in recognizing and defining hydrobiid clades, although features having utility for species-rank descriptions are summarized in an appendix. For 202 characters, sufficient information was available to delineate states and tentatively identify plesiomorpbic conditions (based on outgroup comparisons). Features utilized are from the shell (29 characters), operculum (13), external features (32), pallial cavity (10), digestive system (29), life history (6), female reproductive system (52), and male reproductive system (31). Discussion of many characters is augmented by schematic diagrams and in almost all cases by reference to taxa and published figures illustrating given states. Many characters are extensively annotated, and in some cases new concepts of homology and/or division of characters are proposed. OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Annals of the Smithsonian Institution. SERIES COVER DESIGN: The coral Montastrea cavernosa (Linnaeus). Library of Congress Cataloging-in-Publication Data Hershler, Robert. A review of morphological characters of hydrobioid snails / Robert Hershler and Winston F. Ponder. p. cm. — (Smithsonian contributions to zoology ; no. 600) Includes bibliographical references. 1. Hydrobiidae—Morphology. 2. Mesogastropoda—Morphology. I. Ponder, W. F. II. Title. III. Series. QLI.S54 no. 600 [QL430.5.H9] 590 s—dc21 [571.3' 1432] © The paper used in this publication meets the minimum requirements of the American National Standard for Permanence of Paper for Printed Library Materials Z39.48—1984. Contents Page Introduction 1 Methods 2 Acknowledgments 3 Description of Characters 3 Shell 3 Protoconch 3 Teleoconch 5 Operculum 8 Head-Foot 10 Cephalic Tentacles 10 Snout 12 Neck 13 Foot 13 Pallial Cavity 16 Ctenidium 16 Osphradium 18 Hypobranchial Gland 18 Digestive System 18 Radula 18 Digestive System Apart from Radula 24 Life History 25 Female Reproductive System 26 Genitalia 26 Sperm Storage 31 Sites with Oriented Sperm 31 Sites with Unoriented Sperm 31 Sites with Sperm of Unknown Orientation 34 Oviduct Glands 34 Point of Entry of Sperm 35 Pallial Genital Opening(s) 35 Male Reproductive System 37 Genitalia Apart from Penis 37 Penis 39 Nervous System 42 Other Anatomical Features 42 Appendix: Characters Used to Distinguish Species of Hydrobioid Snails 43 Literature Cited 49 in Dedication To George M. Davis, who has spearheaded modern study of hydrobioid systematics and inspired many students of the group, including ourselves. A Review of Morphological Characters of Hydrobioid Snails Robert Hershler and Winston F. Ponder Introduction of anatomical structures, however, particularly study of histological details, can considerably improve character defini- The incorporation of cladistic methodology into systematic tion and can be applied to well-fixed museum material. and evolutionary studies of Mollusca has been a slow process Among the mollusks, the small-sized aquatic snails of the compared to that involving other large groups, such as insects family Hydrobiidae are especially promising candidates for and vertebrates. This may be due in part to the far greater evolutionary studies because they are extremely diverse (the number of active students of those groups, but it also reflects family contains more than 1,000 Recent species (Boss, 1971) the traditional approach of many practicing malacologists, the and over 400 Recent and fossil genera (Kabat and Hershler, perception that mollusks generally are unsuited for cladistic 1993)), are an old group (which has been diversifying since the analysis owing to paucity of characters and extensive homo- late Paleozoic; Solem and Yochelson, 1979), exhibit consider- plasy (Gosliner and Ghiselin, 1984; Gosliner, 1985; Hershler able morphological variation (e.g., Hershler and Thompson, and Thompson, 1992), and the reality that much emphasis still 1992), and have distributional, ecological, and life history must be focused on describing these poorly known animals. attributes that render them ideal for inquiries ranging from The soft bodies of mollusks and their "plastic" shells lends to biogeography on the global scale (Taylor, 1988) to local an interpretation (albeit largely untested) that morphological investigations of speciation (e.g., Ponder et al., 1994). The convergence is the rule and identification of unique synapo- currently chaotic state of hydrobiid taxonomy at virtually all morphy is the exception in this group. Anatomical characters ranks (Kabat and Hershler, 1993) provides an additional reason can, however, be usefully employed in cladistic analyses of for preparing a rigorous phylogenetic framework for the family. gastropods if recognized states are truly homologous and are as This paper is intended as a forerunner to such an analysis. finely discriminated as possible (Ponder and Lindberg, 1997). Ponder's (1988b) analysis of rissooidean (the superfamily to Much putative homoplasy is undoubtedly the result of which the hydrobiids belong) phylogeny detailed relationships inadequate character definition. Relatively sophisticated stud- between hydrobiids and related family groups. The related ies, employing ontogenetic, histochemical, ultrastructural, and family Pomatiopsidae has been subject to a series of phylo- molecular methodologies, will be required in some cases to genetic analyses by Davis and collaborators, initially based on confidently determine homology, but these methods are time set theory or generated by hand (e.g., Davis and Greer, 1980; consuming (therefore expensive) and are often impossible to Davis et al., 1983; Davis and Silva, 1984) but later derived apply to existing museum material. More precise examination using parsimony algorithms (Davis et al., 1984; Davis, 1992; Davis, Chen, Zeng, et al., 1994). There have been few such studies of hydrobiids, and of these the only analyses using parsimony are by Ponder and Clark (1990), Altaba (1993), Robert