Taxonomic reappraisal of species assigned to the North American freshwater gastropod subgenus Natricola (Rissooidea: Hydrobiidae)

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The hydrobiid gastropod subgenus Natricola (currently placed in synonymy with Pyrgulopsis) was erected for three species from the northwestern United States which have a large shell and long accessory process on the penis. Two of these are restricted to the Snake River basin (P. idahoensis, P. robusta) while the third ranges among Snake River and Great Basin drainages (P. hendersoni). A possible additional species of this subgenus was recently discovered in the Columbia River. In this paper the authors evaluate the taxonomic status of these closely similar and little studied gastropods. Review of morphology demonstrated extensive overlap or only slight differences in taxonomic characters previously utilized to diagnose these snails. Analyses of mitochondrial (cytochrome c oxidase) and nuclear (first internal transcribed spacer region) DNA sequences congruently depicted a strongly supported but weakly structured clade composed of these species. Sequence divergences among these species were markedly lower than those documented for other species of Pyrgulopsis and for other congeneric freshwater mollusks. Based on the results of morphological and genetic studies, P. idahoenis (Pilsbry, 1933), P. hendersoni (Pilsbry, 1933), and the Columbia River population are placed in synonymy with P. robusta (Walker, 1908), which is redescribed herein. Genetic data also suggest that the middle Snake River populations which have been ruled endangered (P. idahoensis) may be appropriately treated as a management unit of P. robusta.

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ELECTRONIC FILE - Zoology: Invertebrates

Hershler, Robert, and Hsiu-Ping Liu. 2004. Taxonomic reappraisal of species assigned to the North American freshwater gastropod subgenus <i>Natricola</i> (Rissooidea: Hydrobiidae). Veliger 47(1): 66-81.