The freshwater mussel genus Oxynaia Haas, 1911 is thought to be comprised of two geographically disjunct and morphologically variable species groups but the monophyly of this taxon has yet to be tested in any modern cladistic sense. This generic hypothesis has important systematic and biogeographic implications as Oxynaia is the type genus of the currently recognized tribe Oxynaiini (Parreysiinae) and is one of the few genera thought to cross several biogeographically important barriers in Southeast Asia. Morphological and molecular data clearly demonstrate that Oxynaia is not monophyletic, and the type species and its allies (O. jourdyi group) belong to the Unioninae, and more specifically as members of the genus Nodularia Conrad, 1853. Therefore, neither Oxynaia syn. nov. nor Oxynaiini Starobogatov, 1970 are applicable to the Parreysiinae and in the absence of an available name, Indochinella gen. nov. and Indochinellini trib. nov. are described. Several combinations are proposed as follows: Indochinella pugio (Benson, 1862) gen. et comb. nov., Nodularia jourdyi (Morlet, 1886) comb. res., N. gladiator (Ancey, 1881) comb. res., N. diespiter (Mabille, 1887) comb. res. and N. micheloti (Morlet, 1886) comb. res. Finally, we provide an updated freshwater biogeographic division of Southeast Asia.