Phylogeny and Species Delimitation in the Land Snail Genus Chilostoma (Gastropoda: Helicidae) and East–West Alpine Disjunctions

Chilostoma includes large, mostly rock‐dwelling snail species, widespread in the European Alps and the Apennines in Italy. We analysed the phylogenetic relationships and the species delimitation of the Chilostoma ( Chilostoma ) species based on genomic ddRAD loci. The Chilostoma ( Chilostoma ) taxa form three sister pairs. Chilostoma achates and C. zonatum are a vicariating East–West Alpine sister species pair, the sister group of all other Chilostoma ( Chilostoma ) species. The high Alpine taxa C. hermesianum and C. liguricum , which were previously classified as subspecies of C . ( Cingulifera ) cingulatum , form another East–West Alpine pair, belonging to C. frigidum . The sister group of C. frigidum comprises C. foetens and C. tigrinum . Chilostoma foetens includes the genetically and morphologically variable populations from the Bergamasque Prealps classified so far as C. adelozona , the populations from the Rhaetian Alps ( rhaeticum ), and the populations from the Aosta Valley and the Lower Valais ( foetens ). The latter population groups are nested in the populations from the Bergamasque Prealps. The population of C. tigrinum from the Cottian Alps is nested in the populations from the Bergamasque Prealps. There are also several East–West Alpine disjunctions in other land snail taxa. These disjunctions are partly caused by a gap of limestone between the Bergamasque Prealps and the Maritime and Ligurian Alps. The crystalline rocks in this region are not suitable for all land snail species. The East–West Alpine disjunctions are remnants of larger distribution ranges, or of long‐distance dispersal events from the east to the west.