Historical Biogeography of Freshwater Planarians (Tricladida, Dugesia ) From the Eastern Palearctic–Oriental Region, Including the Integrative Description of Two New Species From the Nanling Mountains, China

ABSTRACT In this paper we document further samplings in the Nanling Mountains, covering six new localities and infer the historical biogeography of Dugesia from the Eastern Palearctic–Oriental region, thus providing preliminary insights into the mechanisms underlying the formation of their biodiversity in this area. From these six new localities, two new species of freshwater flatworm of the genus Dugesia are described by applying an integrative approach to taxonomy, combining morphological, karyotype and molecular information: Dugesia pyriformis Chen, Dong & Sluys, sp. nov. and Dugesia prominens Chen, Dong & Sluys, sp. nov. Furthermore, our molecular data uncovered cryptic species diversity, enabling taxonomic assignment of several asexual populations to confirm candidate species and thus pointing to at least four more species of the genus Dugesia being present in the Nanling Mountains. Our results also reveal that the Nanling Mountains, which house multiple Dugesia lineages, serve not only as a centre of diversification in southern China but also play a crucial role in facilitating the north–south dispersal of Dugesia in China.