Generic revision on the Biwia– Microphysogobio complex (Cypriniformes, Gobionidae) with descriptions of three new genera

The Biwia – Microphysogobio complex, comprising several genera and over 40 valid species, is widely distributed in the freshwater systems of East Asia. Although many species of this complex have been discovered in the past decades, controversy regarding the taxonomic status of these genera still remains. This study revised the Biwia – Microphysogobio complex at the generic level. Based on the morphology of the type species in each genus and various species within this complex, the genus characteristics are described. The morphology of the lip papillae pattern, jaws, and air bladder chambers are key characteristics used to distinguish the genera. With further evidence supported by the molecular phylogenetic relationships reconstructed from mitochondrial genome sequences, each genus in this complex formed a monophyletic group. The previously polyphyletic Microphysogobio is now separated into four genera, rendering the newly defined genus Microphysogobio monophyletic. The other three genera are newly described, i.e., Crossocheilogobio , Mesophysogobio , and Oriengobio . Along with Biwia , Huigobio , and Platysmacheilus , the complex now includes seven genera. The distribution of each genus is mapped separately in this study. A diagnostic key to genera is provided, and species included in each genus are listed. Sixteen new combinations are generated in this study.