SPB Academic Publishing bv, The Hague Zoogeography of North American hydrobiid cavesnails Robert Hershler1 & John R. Holsinger2 1 Department of Invertebrate Zoology, National Museum of Natural History, Smithsonian Institution, 2 Department of Biological Sciences, Old Dominion University, Norfolk, VA 23529, U.S.A. Keywords: Gastropoda Hydrobiidae, cavesnails, N. America Summary philes, presentes dans des habitats aussi bien epiges que souter- rains. Trois des sous-families sont des groupes dulcicoles anciens (probablement plus anciens que la separation de la Laurasie) et North American hydrobiid cavesnails are moderately diverse ne presentent pas d'etroites affinites avec les taxa coders d'eau taxonomically, including 36 species representing 15 genera and saumatre. Les genres Amnicola (Amnicolinae) et Fontigens four subfamilies. This exclusively freshwater fauna is deployed (Emmericiinae) comprennent des especes epigees, stygophiles, in eastern United States and small areas of south-central Texas ainsi que stygobiontes, presentant une forte similarity avec des and northeast Mexico. Most of the snails are stygobionts (obli- gastropodes d'Europe, tandis que les affinites d'un genre d'am- gate aquatic subterranean forms without eye and body pigment), nicolides encore non decrit, d'Alabama, restent incertaines. Les while five species of Fontigens are stygophiles (occurring in both stygobiontes de la sous-famille des Lithoglyphinae sont re- epigean and hypogean habitats). Three of the above subfamilies presented par deux groupes de relictes anciens descendant peut- are old freshwater groups (probably predating break-up of etre d'ancetres epiges lotiques; un groupe est represents par le Laurasia) with no close relationships to brackish water, coastal genre Phreatodrobia du Texas, le second habits des zones large- taxa. Both Amnicola (Amnicolinae) and Fontigens (Emmericii- ment disjointes: Mexique (Pterides), Alabama (n. gen.), Virginie nae) include epigean or stygophile species as well as stygobionts, (Holsingeria). Les stygobiontes de la sous-famille des Littori- and are closely similar to European snails, while affinities of an dininae (comprenant deux groupes au Texas et au nord du undescribed stygobiont amnicolid genus from Alabama are un- Mexique, et un autre dans le bassin superieur du Mississippi) ont certain. Lithoglyphine stygobionts comprise two groups of old de proches parents dans des eaux cotieres (saumatres); certaines relicts presumably derived from epigean, lotic ancestors: one de ces especes pourraient etre des relictes ayant envahi les eaux from Texas (Phreatodrobia), and the other from widely disjunct douces a la suite d'une regression marine au niveau de bales du locales in Mexico (Pterides), Alabama (n. gen.), and Virginia Cretace Superieur. (Holsingeria). Littoridinine stygobionts (comprising two groups from Texas/northern Mexico and one from Upper Mississippi drainage) have close relatives in coastal/brackish waters and Introduction some may be relicts that invaded freshwater following regression of late Cretaceous marine embayments. Prosobranch snails of the family Hydrobiidae are the only molluscan group extensively deployed in Resume underground aquatic habitats. Apart from the huge subterranean hydrobiid (hereafter referred to as La diversite taxonomique des gastropodes aquatiques souter- cavesnails) assemblage of Europe, which totals over rains d'Amerique du Nord est moderee: 36 especes appartenant 250 species in 60 genera (Willman & Pieper, 1978; a 15 genres et 4 sous-families. Cette faune exclusivement d'eau Bole & Velkovrh, 1986), there are smaller but sig- douce est representee a Test des Etats Unis et dans de perils ter- nificant faunas in North America, Japan, and New ritoires du centre-sud du Texas et du Mexique du nord-est. La plupart de ces gastropodes sont des stygobiontes (formes aqua- Zealand; as well as cavesnail records from many tiques strictement souterraines depourvues d'yeux et de pig- other areas where this cosmopolitan family occurs. ment du corps), tandis que 5 especes de Fontigens sont stygo- Bole & Velkovrh (1986) estimated that 97% of all R. Hershler & J.R. Holsinger - North American aquatic cavesnails Table I. Subterranean hydrobiid snails of North America (including northern Mexico). Totals include undescribed forms. Taxon Total Stygobiont Distribution species species Amnicolinae Amnicola 12 Eastern, northern United States N. gen. 1 1 Enconfina Basin (northwest Florida) Emmericiinae Fontigens 9-10 Eastern, central United States Lithoglyphinae Holsingeria Powell, Shenandoah Basins (Virginia) Phreatoclrobia South-central Texas Pterides Rio Panuco Basin (northeast Mexico) N. gen. 2 Coosa Basin (northeast Alabama) Littoridininae Antrobia White Basin (southwest Missouri) Antroselates Ohio Basin (Kentucky, Illinois) Bulconorbis Nueces Basin (south-central Texas) Coahuilix Rio Salado Basin (northeast Mexico) Emmericiella Rio Panuco Basin (northeast Mexico) Paludiscala Rio Salado Basin (northeast Mexico) Phrealoceras Southwest Texas, northeast Mexico Srygopvrgws Colorado Basin (south-central Texas) N. gen. 3 Devils, Rio Grande Basins (south-central Texas) 'Remaining congeners occur in both epigean and subterranean aquatic habitats. mollusks associated with continental subterranean stygophiles, as they occur in both epigean and waters are hydrobiids. hypogean habitats. Hydrobiid cavesnails of North America (includ- While the first North American cavesnail was ing northern Mexico) are a modest-sized group described in 1838 (Paludina nickliniana Lea), most (ranking second to that of Europe among continen- of the fauna (including virtually all of the stygo- tal faunas) comprising 36 species representing 15 bionts) was only recently discovered by or through genera and four subfamilies (Table 1). Cavesnails the efforts of Leslie Hubricht and Joseph Morri- occur in many of the major limestone areas of son, who commenced their long field careers during North America, although their absence from karst the 1930s. Modern taxonomic study of the fauna areas of western United States and poor representa- was initiated during the past decade, and descrip- tion in the Interior Low Plateaus are noteworthy tions of shell and anatomy of most of the known (Fig. 1). All of these snails are exclusively fresh- taxa now are published or in press. The senior water: they may be collected from subsurface author participated in much of this taxonomic habitats that include outflows of springs of various work (see Hershler, 1985, 1989; Hershler & Hu- sizes, cave streams, and phreatic waters delivered bricht, 1988; Hershler & Longley, 1986a, 1986b, by wells. Local diversity usually is low, with a maxi- 1987; Hershler & Thompson, in press; Hershler et mum of two sympatric species found at most locali- al., in preparation; Thompson & Hershler, in ties (note, however, that five Phreatoclrobia spp. preparation) and has studied virtually all members have been collected from orifices of the large San of this fauna. Marcos Springs, Hays County, Texas). Of the 36 The purpose of this paper is to describe zoogeo- species, thirty-one (86%) are stygobionts, or ob- graphic patterns of the North American cavesnails. ligate subterranean species, characterized by loss of Basic data including distributions and phylogenetic body and eye pigment. Another five species (all relationships of the snails (at the generic level) are members of the genus Fontigens) may be termed summarized and briefly analyzed in relation to Sfygo/ogfa J W - /9P0 Fig. I. Map of the conterminous United States and northern Mexico showing distribution of major limestone cave areas (stipple) and occurrences of stygobiont hydrobiid cavesnails (filled circles and black areas) (modified from Tamayo 1964; Barr & Holsinger 1985). hypothesized vicariant and/or dispersal events of relationships using morphological criteria are par- presumed importance to the evolutionary history of ticularly difficult to obtain for cavesnails because these snails. This paper updates an earlier review by of anatomical simplification and convergence as- Morrison (1949), whose conclusions in part are sup- sociated with their characteristic reduced size (com- ported by additional evidence provided herein. pared to epigean counterparts, an anecdotal trend Our conclusions are preliminary, as both the dis- lacking statistical confirmation). Features appar- tribution and phylogenetic relationships of North ently associated with snail miniaturization (which American cavesnails require much additional itself may be an ecological correlate of a stygobiont study. Sampling by no means is routine: while col- habit) include complex coiling of the intestine, loss lection of live examples of suspected cavesnails or reduction of ctenidium, simplification of gona- usually can be accomplished given sufficient time, dal morphology, and loss of sperm sacs. Given this effort and ingenuity, detailed documentation of situation, together with the currently inadequate subterranean range of these organisms presents supra-generic classification of hydrobiids (in which enormous difficulties that rarely have been over- various family-level groups probably represent come in anything other than relatively small re- grades rather than clades), the cladistic analyses gions. Further, robust assessments of phylogenetic presented below must be considered "working R. Hershler & J.R. Holsinger - North American aquatic cavesnails hypotheses" to be modified pending acquisition of Zoogeographic patterns additional morphological