An integrative analysis and account of two new species of Dugesia (Platyhelminthes, Tricladida, Dugesiidae) from the Hengduan Mountains, southwest China, with reflections on the historical biogeography of Eastern Palearctic/Oriental lineages

Two new species of the genus Dugesia from southwest China are described using an integrative approach based on morphological, histological, and molecular data. Dugesia patula Chen & Dong, sp. nov. is characterized by the following features: symmetrical openings of the oviducts into the bursal canal; vasa deferentia opening symmetrically into the mid-lateral portion of the seminal vesicle; a large and pointed diaphragm; a short duct between the seminal vesicle and diaphragm; and a very broad, short ejaculatory duct with a very wide opening at the tip of the penis papilla. Dugesia postica Chen & Dong, sp. nov. , is characterized by the following features: symmetrical openings of the oviducts into the bursal canal; a small penis bulb; a large and long penis papilla with a slightly larger dorsal lip and a small ventral lip; a long connecting duct between the seminal vesicle and diaphragm; a small diaphragm located near the tip of the penis papilla; and an extremely short ejaculatory duct. In the molecular phylogenetic tree, the two new species share a sister-group relationship and fall within an eastern Palearctic/Oriental clade of conspecifics. The distinct specific status of these two new species is also supported by their genetic distances. Through a multi-gene concatenated phylogenetic analysis, this study, for the first time, elucidates the evolutionary relationships among the Oriental, eastern Palearctic, and Australasian groups, enabling the development of a hypothesis on the potential dispersal routes of Dugesia into the eastern Palearctic region.