A new genus of freshwater crab from Vietnam, with comments on the allied genera Vietorientalia Đặng, 2012, and Hainanpotamon Dai, 1995 (Decapoda, Brachyura, Potamidae).

The nomenclatural history and taxonomic problems associated with two poorly known Vietnamese potamid freshwater crab species assigned initially to Hainanpotamon Dai, 1995, and later to Vietorientalia Đặng, 2012, viz., V. glabra (Đặng, 1967) and V. rubra (Đặng & Trần, 1992), are addressed. Clear morphological and molecular evidence confirms the validity of Vietorientalia, and a neotype is herein designated for the type species, V. glabra, for which the type material is purportedly lost. Moreover, morphological and molecular evidence suggests that the two species currently assigned to Vietorientalia are non-congeneric. Accordingly, a new genus, Dangmon gen. nov., is herein erected to accommodate V. rubra.