The Tribe Alasmidontini (Unionidae: Anodontinae), Part I: Pegias, Alasmidonta, and Arcidens ARTHUR H2 CLARKE SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 326 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 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 cf 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. S. Dillon Ripley Secretary Smithsonian Institution SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 326 The Tribe Alasmidontini (Unionidae: Anodontinae), Part I: Pegias, Alasmidonta, and Arcidens Arthur H. Clarke SMITHSONIAN INSTITUTION PRESS City of Washington 1981 ABSTRACT Clarke, Arthur H. The Tribe Alasmidontini (Unionidae: Anodontinae), Part 1: Pegias, Alasmidonta, and Arcidens. Smithsonian Contributions to Zoology, number 326, 101 pages, 32 figures, 24 tables, 1981.—The taxonomy, morphology, life history, and distribution of fourteen species, comprising four traditional genera, are described. Discussions of morphology include descriptions of the shell, anatomy, and glochidium (where possible) of each species and of character variation, together with statistical tables, illustrations, and scanning electron microscope photographs. Distributional data include organized lists of all museum material, with distribution maps, and with special reference to recently collected specimens that are likely to represent living populations. Also discussed are some quantitative effects of water hardness and temperature on shell weight and on characters linked with shell weight, new glochidial characters as observed with the scanning electron microscope, the indirect determination of sex in non-gravid specimens by examination of the demi- branchs (Ortmann's method), and taxonomic relationships of the Tribe Alasmidontini. Species recognized are: Pegias fabula (Lea), Alasmidonta {Presso- donta) viridis (Rafinesque), A. (P.) heterodon (Lea), A. (Alasmidens) mccordi Athearn, A. {Alasmidonta) undulata (Say), A. (A.) arcula (Lea), A. (A.) wrightiana (Walker), A. (Decurambis) marginata Say, A. (D.) atropurpurea (Rafinesque), A. (D.) raveneliana (Lea), A. (D.) varicosa (Lamarck), A. (/).) robusta (new species), Arcidens (Arkansia) wheeleri (Ortmann and Walker), and A. {Arcidens) confragosus (Say). A new subgenus, Alasmidens, is described. OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Smithsonian Year. SERIES COVER DESIGN: The coral Montastrea cavemosa (Linnaeus). Library of Congress Cataloging in Publication Data Clarke, Arthur Haddleton, 1926- The tribe Alasmidontini (Unionidae, Anodontinae) (Smithsonian contributions to zoology ; no. 326) Bibliography: v. 1, p. CONTENTS: pt.l Pegias, Alasmidonta, and Arcidens. 1. Unionidae—Classification. 2. Mollusks—Classification. I. Title. II. Title: Alasmidontini (unionidae, Anodontinae) III. Series: Smithsonian Institution. Smithsonian contributions to zoology ; no. 326- QL1.S54 no. 326, etc. [QL430.7.U6] 591s [594'. 11] 80-23747 Contents Page Introduction I Scope 1 Shell Characters and Water Quality 2 Glochidial Characters 5 Indirect Determination of Sex 7 Taxonomic Relationships of the Alasmidonta Complex 7 Acknowledgments 8 Genus Pegias Simpson, 1900 9 Pegiasfabula (Lea, 1838) 9 Genus Alasmidonta Say, 1818 15 Subgenus Pressodonta Simpson, 1900 17 Alasmidonta (Pressodonta) viridis (Rafinesque, 1820) 17 Alasmidonta (Pressodonta) heterodon (Lea, 1830) 28 Subgenus Alasmidens, new subgenus 35 Alasmidonta (Alasmidens) mccordi Athearn, 1964 35 Subgenus Alasmidonta, sensu stricto 37 Alasmidonta (Alasmidonta) undulata (Say, 1817) 38 Alasmidonta (Alasmidonta) arcula (Lea, 1838) 48 Alasmidonta (Alasmidonta) wrightiana (Walker, 1901) 54 Subgenus Decurambis Rafinesque, 1831 57 Alasmidonta (Decurambis) marginata Say, 1818 57 Alasmidonta (Decurambis) atropurpurea (Rafinesque, 1831) 67 Alasmidonta (Decurambis) raveneliana (Lea, 1834) 71 Alasmidonta (Decurambis) varicosa (Lamarck, 1819) 75 Alasmidonta (Decurambis) robusta, new species 81 Genus Arcidens Simpson, 1900 84 Subgenus Arkansia Ortmann and Walker, 1912, new status 85 Arcidens (Arkansia) wheeleri (Ortmann and Walker, 1912) 85 Subgenus Arcidens Simpson, sensu stricto 89 Arcidens (Arcidens) confragosus (Say, 1829) 89 Literature Cited 98 in The Tribe Alasmidontini (Unionidae: Anodontinae), Part 1: Pegias, Alasmidonta, and Arcidens Arthur H. Clarke Introduction indirect determination of sex in non-gravid spec- imens, and the taxonomic placement of the Alas- SCOPE.—This is a taxonomic revision of the midonta complex. The systematics section contains Alasmidonta complex, a related assemblage of 14 accounts of the taxonomy, morphology (descrip- species of freshwater mussels traditionally com- tions of shells, anatomy, and glochidia, and anal- prising the nominal genera Alasmidonta Say yses of their variation), life history, and geograph- (1818), Pegias Simpson (1900), Arcidens Simpson ical distribution of each species, distribution (1900), and Arkansia Ortmann and Walker (1912). maps, illustrations and SEM photographs. The All of them live in rivers and several are found sections on geographical distribution consist of only near riffles or rapids where the water is well organized lists, arranged by river systems, of all oxygenated. Nine of the species, at best, are either of the documented site records available from the uncommon, rare, or very rare; in fact, three of writer's field work, from museum collections, and these appear to have become extinct in this cen- from the primary literature. Collections made tury. In general ecology and in status of endan- since 1950 are identified by collector and date germent they resemble another group of unionids because those are most likely to reflect the present in another subfamily (Lampsilinae), variously occurrence of living populations. recognized under the names Dysnomia Agassiz The specimen records listed are principally (1852), Epioblasma Rafinesque (1820), and Plagiolathose from the collections of the Academy of Rafinesque (1820), and recently thoroughly mon- Natural Sciences of Philadelphia (ANSP); the ographed by Johnson (1978). Museum of Comparative Zoology, Harvard Uni- This paper has two parts, a general introduc- versity (MCZ); the National Museum of Natural tory section and a systematics section. The first Sciences, National Museums of Canada (NMC); part contains discussions of some effects of water the National Museum of Natural History, Smith- quality on established taxonomic characters, sonian Institution (USNM); the Ohio State Uni- some new taxonomic characters of glochidia, the versity Museum of Zoology (OSUM). Those col- lections produced so many records that the geo- graphical distributions of most species were Arthur H. Clarke, Ecosearch, Inc, 7 Hawthorne Street Mattapoisett, Massachusetts 02739. clearly defined. To save space, records from the 1 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY large and important collection at the University group (the St. Lawrence River System in Ontario of Michigan Museum of Zoology (UMMZ), and and Quebec to the Chattahoochee River System other sources, have been cited only in cases where in Florida), by examining and measuring these they further extend the ranges of the species specimens for all characters that appear to be concerned. revealing or have been used by other investigators For identification of species treated in this pa- to define taxa, and by comparing these results per one should first make a tentative identifica- with the parameters of water quality about which tion by using the illustrations and the distribution data are available and which appear to be sig- maps and then confirm that identification by nificant. reading the text. Characters are described in the The specimens used in the investigation are in same sequence under each species and detailed the Museum of Comparative Zoology, the Na- comparisons of species are therefore