When morphology meets molecules: diversity of dart-bearing Hygromia Risso, 1826 land snails (Gastropoda: Hygromiidae)

The actual diversity of Hygromia land snails is unknown. Typically, three or four species were recognized based on morphology. Here, we applied an integrative taxonomic approach to assess species limits through combined analyses of shell and genital morphology, including love darts, as well as genetic data in 205 specimens from 90 localities across Europe. The results revealed two monophyletic groups of populations that were more similar in their shell morphology and differed in the size of the dart apparatus. They represented two subgenera with seven mtDNA clades. The subgenus Hygromia s.s. consisted of a nominal Hygromia cinctella. The subgenus Riedelia included: Hygromia limbata s.s. and its subspecies Hygromia limbata hylonomia, Hygromia tassyi and Hygromia pyrenaica sp. nov. The taxonomic status of two independently evolving lineages could not be resolved. Hygromia odeca and Hygromia veprium were synonymized with Hygromia limbata and Hygromia gofasi with Hygromia tassyi. No morphometric shell character alone ensured the determination of any Hygromia species and the microsculpture showed only minor differences. Among genitalia features, the appearance of a love dart had the greatest taxonomic value. Many recognized taxa were restricted to narrow territories, implying a complex evolutionary history of the genus in the Pyrenees and their foothills.