A SYSTEMATIC REVIEW OF THE HYDROBIID SNAILS (GASTROPODA, RISSOOIDEA) OF THE GREAT-BASIN, WESTERN UNITED-STATES - PART I - GENUS PYRGULOPSIS

A recently completed field survey of springs throughout the Great Basi n yielded collections of hydrobiid snails from more than 500 sites, an d revealed a wealth of undescribed diversity of these small gastropods . In this, the first of a two-part taxonomic series treating this mate rial, 58 new species of Pyrgulopsis Call & Pilsbry, 1886, are describe d; and new records are provided for 10 previously described members of this genus. Assignment of these novelties to Pyrgulopsis is done with the acknowledgement that this large genus, as currently constituted, is probably not monophyletic, but a more refined classification of the se snails reflecting evolutionary relationships must await preparation of a phylogenetic analysis, which is beyond the scope of this work. P yrgulopsis occur in a variety of spring-fed water bodies in the Great Basin, including brackish and/or thermal habitats. Although a few spec ies are widespread in the region, local endemism is prevalent and 22 o f the new species are known only from single localities. Several areas contain concentrations of locally endemic snails which may represent species flocks, notably Duckwater Valley (seven species) and southern Steptoe Valley (five species). This fauna is largely distributed in an allopatric fashion, although a few springs harbor two or three specie s. Most of the springs inhabited by hydrobiids in the region are small , fishless, and have been ignored by state and federal land management agencies. However, many of these sites are degraded by livestock graz ing, water withdrawal, and other activities and will require protectio n in order to conserve snails and other native aquatic biota. Two of t he novelties described herein have become extinct during the past two decades.