Morphological and molecular phylogenetic studies of a newly-recorded Gymnothorax species in China Sea——G. sagmacephalus

Genus Gymnothorax is one of the most diverse, abundant and widely distributed genera of moray eels in the family Muraenidae; there were more than 100 valid species of Gymnothorax all over the world and approximately 20-30 species recorded in China. It was a poorly known group in China, with very few studies focusing on it. To improve the species list information of the Gymnothorax resource, this study reported a newly-recorded species, G. sagmacephalus Böhlke, 1997, which was previously only recorded in Japan and eastern Taiwan, China. Two individuals of the species were collected from the coastal area of Xiamen City, Fujian Province and Shantou City, Guangdong Province. The detailed morphological characteristics of the new species were described, and the molecular identification as well as phylogenetic construction were preformed based on DNA barcoding COⅠgene and 16S rRNA gene. The result showed that, the diagnostic characters of G. sagmacephalus were: body coloration light brown, a dusky saddle-like marking on the top of head just behind eyes, and a large prominent dark triangle marking just before the dorsal-fin origin; black stripes on the abdomen extending from the gill opening to the anus; dorsal and anal fins with a white margin; body was elongate, total lengths were 19.06-19.60 times of body height; teeth were uniserial, and maxillary teeth with 8 on each side without additional inner row teeth; number of dentary teeth were 12-14; total vertebrae were 162-168. Based on the analysis of COⅠand 16S rRNA gene, the genetic distance between G. sagmacephalus and related Gymnothorax species with pure body color were: COⅠ(0.120-0.255); 16S rRNA(0.059-0.132). The genetic value of COⅠ were greater than the 2% minimum diagnostic threshold suggested by Herbert, indicating that G. sagmacephalus was an independent species. The molecular phylogenetic tree showed that G. sagmacephalus and G. albimarginatus were tightly clustered as one group, indicating their close relationship. The results clarified that G. sagmacephalus was a newly recorded species and could be found in the coastal water of mainland China, which also provides a taxonomic basis for the systematic classification and the species list revision of the Gymnothorax fish in China.