Identification and DNA Barcoding of a New Sillago Species in Beihai and Zhanjiang, China, with a Key to Related Species

A new Sillago species, Sillago parasihama sp. n., is identified based on 127 specimens collected from the southern coast of China. We compared the morphological characters between Sillago parasihama and all other 11 Sillago species with two posterior extensions on the swim bladder. The new species is like S. sihama in the countable characters and color pattern, but is different from the latter by the distinct swim bladders. The swim bladder of S. parasihama is without lateral process. The posterior sub-extensions of anterolateral extensions are unique with some dendritic or sometimes stunted blind tubule, which are unilateral and outward, extending along the abdominal, and are about one-third to half of the body of swim bladder in length. But the swim bladder of S. sihama with 8–10 lateral processes, the posterior sub-extensions of anterolateral extensions are kinky, long and complicated, extending along the abdominal wall below the peritoneum to the base of posterior extensions. S. parasihama can be distinguished from other species in this group by color pattern, meristic, and morphometric characters. Moreover, the results of genetic analysis using sequences of the mitochondrial cytochrome c oxidase subunit I ( COI ) fragment show significant interspecific-level genetic distances (0.159–0.231) between S. parasihama and 8 congeners in the group, which also support the validity of new species. We also provide a distribution map and a key of the related species.