Abstract
The taxonomic relationships among four stagnicoline snail species from North America were reassessed by analysing nucleotide sequences from their nuclear ribosomal internal transcribed spacer (ITS) region. Three of the species (Stagnicola catascopium, Stagnicola emarginata, and Stagnicola elodes) are representatives of the subgenus Stagnicola s.str. from the northern U.S.A. and the fourth is a closely related Canadian species (Stagnicola caperata) belonging to the subgenus Hinkleyia. Members of the two subgenera differed considerably in their ITS sequences, demonstrating the usefulness of these sequences for distinguishing species from closely related lymnaeid subgenera. In contrast, ITS sequences for the three members of the subgenus Stagnicola s.str. were very similar, which supports an earlier view that they may not be separate species.