Transfer of Cochliopa texana to Pyrgulopsis (Hydrobiidae) and description of a third congener from the lower Pecos River basin

Abstract

The Phantom Cave snail (Cochliopa texana), a little-studied rissooidean gastropod that is locally endemic within the lower Pecos River basin (Texas) and currently a candidate for addition to the Federal list of threatened and endangered species, is redescribed and transferred to the hydrobiid genus Pyrgulopsis, based on shell and anatomical characters. Specimens from the type locality (Phantom Lake Spring) and San Solomon Spring are larger than those from East Sandia Spring and also differ somewhat in shell shape and shape of the central cusps of the lateral radular teeth. However genetic (mtCOI, NDI) variation within and among these geographically proximal (6– 13 km) populations was slight, providing no basis for the recognition of distinct conservation units of this imperiled species. We also describe Pyrgulopsis ignota n. sp., which was recently discovered in a different part of the lower Pecos River basin and initially confused with the Phantom Cave snail. These two species differ in shell shape, operculum morphology, and form and glandular ornament of the penis. They are also strongly differentiated genetically from each other and from (13) other regional congeners ( pairwise sequence divergence .6.3% for both genes). A Bayesian phylogenetic analysis of the COI and NDI dataset indicated that these two snails are not closely related and that P. ignota occupies a basal position relative to other regional congeners.