Two new species of freshwater planarian from Hainan Island and Leizhou Peninsula, southern China (Platyhelminthes, Tricladida, Dugesiidae)

Two new species of the genus Dugesia from Hainan Island and Leizhou Peninsula are described by applying an integrative approach, including morphological, karyological, histological, and molecular information. In the molecular phylogenetic tree, the two new species, Dugesia saccata Chen & Dong, sp. nov. and Dugesia aconcinna Chen & Dong, sp. nov., fall into an Eastern Palearctic / Oriental clade and an Oriental / Australasian clade, respectively, while sharing only a rather distant relationship.

The separate specific status of the two new species is supported also by their genetic distances. Dugesia saccata is characterised by the presence of the following features: a sac-shaped expansion at the knee-shaped bend of the bursal canal; ventrally displaced ejaculatory duct with a subterminal opening; a duct between diaphragm and seminal vesicle; mixoploid karyotype with diploid complements of 2 n = 2 x = 16 and triploid complements of 2 n = 3 x = 24, with all chromosomes being metacentric.

Dugesia aconcinna is characterised by the presence of the following features: asymmetrical openings of the oviducts into the bursal canal and the common atrium, with the left oviduct opening into the common atrium and the right oviduct opening into the most ventral, proximal portion of the bursal canal, at the point where the latter communicates with the common atrium; vasa deferentia separately opening into the posterior portion of the seminal vesicle; penis papilla of a very characteristic shape, with the part housing the connecting duct, diaphragm, and ejaculatory duct being a cylindrical structure with a blunt tip, while at its right-hand side sits a large penial fold that attaches to the base of the penis papilla; ejaculatory duct following a ventrally displaced course through the penis papilla, after which it opens at the tip of the papilla; presence of a duct between diaphragm and seminal vesicle.