We analysed cytochrome c oxidase subunit I and NADH dehydrogenase subunit I sequence variation among 29 populations of a widely ranging southwestern springsnail (Pyrgulopsis micrococcus) and 18 regional congeners. Cladistic analyses of these sequences depict P. micrococcus as a polyphyletic composite of five well-supported clades. Sequence divergences among these clades and subclades imply the possible occurrence of as many as seven or eight cryptic species in addition to P. micrococcus. Our finding that P. micrococcus contains multiple, genetically distinct and geographically restricted lineages suggests that diversification within this highly speciose aquatic genus has been structured in large part by the operation of terrestrial barriers to gene flow. However, these sequence data also indicate that recent dispersal among hydrographically separated areas has occurred within one of these lineages, which we attribute to passive transport on migratory waterbirds.

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Springsnails (genus Pyrgulopsis) are one of the most abundant and diverse members of the endemic western North American aquatic biota. These tiny gastropods are imperiled by threats ranging from groundwater pumping to livestock grazing. During the past 25 years, this longneglected element of biodiversity has emerged as a new focus of conservation-related activities, including protection of several species under the Endangered Species Act and monitoring and habitat restoration efforts. Molecular investigations have helped sharpen springsnail taxonomy and suggest that these animals cannot be managed using a priori assumptions of population structure. Despite this progress, there is an urgent need for additional studies of springsnail natural history, taxonomy, and genetics. The prospects for improving the protection and restoration of springsnail habitats are promising but are clouded by the overarching threat of groundwater mining, which may be addressed best by broader conservation efforts focused on regional groundwater-dependent ecosystems.

The Preble's meadow jumping mouse (Zapus hudsonius preblei) is listed as a threatened subspecies under the United States Endangered Species Act (US‐ESA). The quantitative description of this subspecies was based on cranial measurements of only three adult specimens. It is one of twelve subspecies of Z. hudsonius and is a peripheral population at the western edge of its range. We tested the uniqueness of Z. h. preblei relative to other nearby subspecies of Z. hudsonius using a hypothesis testing approach and analyses of cranial morphometric, mtDNA sequence and nuclear microsatellite data obtained from museum specimens and archived tissues. Morphometric analysis of variance did not support the original description of Z. h. preblei as a subspecies. Principal component analysis of these data showed Z. h. preblei within the range of variation found in Z. h. campestris and Z. h. intermedius. Discriminant analysis correctly classified only 42% of Z. h. preblei skulls at jackknifed posterior probabilities >0.95 relative to Z. h. campestris. All mtDNA haplotypes found in Z. h. preblei were also found in Z. h. campestris. Simulation based estimates of current and historical gene flow (MDIV) revealed low, but non‐zero, mtDNA gene flow among Z. h. preblei and several nearby subspecies. Analyses of five nuclear microsatellite loci using population pairwise FST, BAPS and STRUCTURE were consistent with morphometric and mtDNA results. These revealed low levels of genetic structure and evidence of recent gene flow and bottlenecks in Z. h. preblei. Due to a lack of clearly recognisable genetic, morphological, or adaptive differences, we synonymise Z. h. preblei and Z. h. intermedius with Z. h. campestris. We suggest that candidates for listing under the US‐ESA, or similar biodiversity laws, be evaluated for genetic and/or morphological uniqueness to prevent the misallocation of resources to non‐distinct taxa like Z. h. preblei.