Splitting the Roman snail Helix pomatia Linnaeus, 1758 (Stylommatophora: Helicidae) into two: redescription of the forgotten Helix thessalica Boettger, 1886
Abstract
The Roman snail Helix pomatia Linnaeus, 1758 is a large terrestrial gastropod very common in central and southeastern Europe, and is the type species of the genus. A recent molecular phylogenetic study has uncovered two divergent lineages within the species as currently conceived.
One represents the true H. pomatia, the second corresponds to a previously recognized subspecies H. pomatia thessalica Boettger, 1886. Using more samples, new molecular data and thorough morphological investigations, we redescribe the latter as a separate species.
Morphological differences, especially colouration and surface sculpture of the shell and dark colouration of distal genitalia, distinguish this taxon reliably from H. pomatia. The species is widespread in the southern Balkans, but its range extends also to central Europe along the Carpathian Arc.
Thus, its distribution broadly overlaps with that of H. pomatia and we have found evidence for occasional hybridization between the two species. Some lineages of H. thessalica seem to be restricted to the Carpathians and their vicinity; these might have survived locally during the last glacial.
By clarifying the taxonomy of H. pomatia, we make the crucial first step towards elucidating the phylogeographic history of this iconic member of the European land snail fauna.