From a monotypic genus to a western Balkan radiation: the remarkable diversity of Xerocampylaea (Gastropoda: Hygromiidae)

The Balkan Peninsula is one of the most important biodiversity hotspots in Europe, but the western Balkans, especially Bosnia and Herzegovina, remain understudied. We studied a poorly known and taxonomically challenging clade of land snails that comprises species previously assigned to the genera Xerocampylaea, Trochulus, Monachoides and Semifruticicola. In a first comprehensive assessment of the group since 1915, we investigated its morphological diversity and mitochondrial phylogeny and we attempted to link these two sources of information with available nominal taxa. A total of 70 populations representing most of the clade’s distribution and ecological ranges were analysed. The oldest available name for the clade is Xerocampylaea, which until the first molecular phylogenetic analyses was considered a monotypic genus. In our preliminary taxonomic treatment, we identified 13 mitochondrial lineages that match a more or less diagnosable morphotype with a defined distribution as well as an available name: X. zelebori, X. erjaveci, X. hirci, X. osoria, X. blaui, X. floerickei, X. costulata, X. waldemari, X. leptolasia, X. serbica, X. fallax, X. taraensis and X. kosovoensis. The combination of microsculpture, genital features and geographic location enables their fairly accurate identification. To stabilize the nomenclature and remove ambiguities in type localities and the interpretation of taxa, we designated five lectotypes and three neotypes. However, there still remain lineages that may represent unnamed species and names that cannot be unambiguously linked to a biological species. Our study of the Xerocampylaea group constitutes a great step towards a better understanding of the complex pattern of genetic and morphological diversity in Balkan land snails, but should be followed by even more detailed studies employing genomic data.