A new cryptic species of Rhinogobius (Gobiiformes: Oxudercidae) from northern Taiwan, with remarks on the cryptic diversity within the Rhinogobius similis species complex.

A new cryptic species of Rhinogobius within the R. similis species complex, Rhinogobius feitsuiensis sp. nov., is described based on 12 specimens collected from the Feitsui Reservoir, northern Taiwan. Although R. feitsuiensis shares the unique transverse cheek papillae pattern typical of the R. similis complex, it differs from the three other species in this complex by having three longitudinal rows of papillae, with three to four transverse rows between the eye and the upper longitudinal row and none between the upper and lower longitudinal rows. Rhinogobius feitsuiensis differs from R. similis by having a shorter second dorsal-fin base (11.9-14.1% SL vs. 17.4-20.6% SL in topotypic R. similis) and body depth at pelvic-fin origin (12.1-14.7% SL vs. 18.3-19.3% SL in topotypic R. similis). Further, R. feitsuiensis also has more pre-dorsal ctenoid scales (12-13 vs. 8-12 in topotypic R. similis). Phylogenetic analysis based on mitochondrial COI gene sequences supports R. feitsuiensis as a well-defined monophyletic lineage. The recognition of R. feitsuiensis increases the number of nominal species within the R. similis complex to four and unravels the cryptic diversity among the Rhinogobius similis complex in East Asia.