Taxonomic identity of the endangered Snake River physa, Physa natricina (Pulmonata: Physidae) combining traditional and molecular techniques

The conservation of some imperiled species has been impaired by taxonomic uncertainty. The Snake River physa, Physa natricina Taylor 1988, is an endangered gastropod to the middle Snake River that has rarely been collected live. The rarity of P. natricina and the lack of live specimens have fueled debate regarding the validity of the species. Our objectives were to: determine if P. natricina existed in a suspected population area; if found, to compare shell morphology to the holotype and soft tissue to the original description; review available museum specimens to determine species range; and phylogenetically compare suspect P. natricina with confamilial and other known Physidae. Sampling yielded suspect P. natricina with shell morphology matching the holotype and dissections revealed that the soft tissue was within the purview of the original description and not overlapping the characters of other Physidae. Review of museum Physidae collected from the Snake River revealed suspect P. natricina as far downstream as RK 592. Physella gyrina was the only confamilial species found during sampling and during review of museum collections. Phylogenetic analyses (maximum parsimony, maximum likelihood, Bayesian inference, and UPGMA) of cytochrome c oxidase subunit I and ribosomal subunit 16S markers strongly supported P. natricina as a reciprocal monophyletic group and a distinct evolutionary significant unit. Our results confirm the original description of P. natricina as a distinct species and expand the extant distribution highlighting the importance of combining traditional methods of taxonomic description with modern molecular tools when working with species of conservation concern.