A New Species of Hemisilurus (Siluriformes, Siluridae) from the Mekong River, with Comments on Its Relationships and Historical Biogeography

Abstract

Hemisilurus mekongensis n. sp. is described from the middle Mekong River basin. It differs from all other species of Hemisilurus in having fewer analand more pectoral-fin rays and a single vomerine tooth patch. Phylogenetic analysis shows that H. mekongensis and H. moolenburghi (from Borneo and Sumatra) are sister species that are distinguished from H. heterorhynchus (of which H. chaperi is a junior synonym) by a smaller eye, absence of pectoral-spine enlargement in males, and a longer maxillary barbel that in large females is distally expanded as a broad membrane that may separate into several fine filaments. Allopatric distributions of H. mekongensis and H. moolenburghi indicate a post-Pleistocene vicariance between drainages of mainland southeast Asia and the Indonesian islands. Sympatry among Hemisilurus species and Ceratoglanis, the sister group to Hemisilurus, indicates post-speciation dispersal between Sunda drainages during lowered Pleistocene sea levels.