Taxonomic identity of two amnicolid gastropods of conservation concern in lakes of the Pacific Northwest of the USA

Abstract

In this paper we attempt to clarify the identity of two purportedly new species of amnicolid snails in Pacific Northwest lakes that were vaguely described in grey literature and recently petitioned for federal listing. As currently understood the western American amnicolid fauna consists of the endemic genus Colligyrus (three species) and Amnicola limosa, which is distributed in a single site in western Montana (and also throughout much of eastern North America). The Washington duskysnail was proposed for the Montana population of A. limosa and two recently discovered populations in northern Washington. The masked duskysnail is a small amnicolid of uncertain generic status from two lakes in northern Washington. Our assessment of these putative species was based on genetic and morphological study of specimens from previously reported sites and recently discovered localities in Montana (both snails) and Washington (the first only). Molecular analyses (based on the mtCOI gene) resolved the western American populations of Amnicola as a weakly supported subunit of a clade that also contained eastern A. limosa and A. dalli; the western Amnicola differed from eastern A. limosa and A. dalli by 2.1% mean sequence divergence. We also found that western Amnicola and eastern A. limosa do not differ in body pigmentation as previously postulated and that these snails are closely similar in all other morphological details. We conclude that the Washington duskysnail is not a distinct species and that all of the western populations of Amnicola are A. limosa. This finding extends the range of A. limosa westward almost to the Pacific margin. Our molecular phylogenetic analyses and study of the female reproductive anatomy of the masked duskysnail congruently indicated that this snail, which was previously compared with other western amnicolids, belongs to the genus Lyogyrus, which is otherwise restricted to eastern North America. We were unable to resolve the taxonomic status of the masked duskysnail further, owing to the paucity of pertinent data for the poorly known eastern Lyogyrus fauna. We recommend that the masked duskysnail be treated as Lyogyrus sp. pending further study of this genus.