Morphological Identification and Complete Mitogenome of a New Record Moray Eel Gymnothorax emmae (Muraenidae) from China Sea

This study reports the first record of Gymnothorax emmae Prokofiev, 2010 in China’s coastal regions. Initially discovered in Vietnam in 2010, this species has not been previously reported in any other global regions. Here the morphological characteristics of G. emmae were described in detail. Additionally, the entire mitochondrial genome of this species was sequenced and assembled, providing molecular evidence for species identification and phylogenetic analysis. Key distinguishing features of G. emmae include: a yellow or yellow-brown body with a lighter head; several rows of brown spots, either rounded or irregular, behind the eyes and in the branchial region; numerous tortuous transverse or oblique brown bands on the trunk and fins, some of which are interconnected; uniserial teeth; and a vertebral count of 3–4/45–47/121–125. The complete mitochondrial genome transfer RNAs of G. emmae was sequenced to be 16 577 bp, encompassing 13 protein-coding genes, 22 transfer RNAs, 2 ribosomal RNA genes, and a non-coding region. The genome organization aligned with that of other Muraenidae species. Phylogenetic relationships were reconstructed to clarify the taxonomic position of G. emmae. Phylogenetic trees were built for 23 Muraenidae species using 12 protein-coding genes, and for 72 Gymnothorax species using the cytochrome c oxidase subunit I (COI) gene. The tree based on 12 protein-coding genes strongly supported that G. emmae was sister to a species complex consisting of Gymnothorax kidako and Gymnothorax niphostigmus. Similarly, the COI-based tree placed G. emmae within a clade containing 7 species (G. kidako, G. niphostigmus, G. mucifer, among others). These species share distinct body coloration and patterns, some of which could be easily confused with G. emmae. Genetic distances, calculated from the COI gene, ranged from 0.072 to 0.262 between G. emmae and other Gymnothorax species, all exceeding the minimum species-identification threshold of 0.020 (2%), confirming that G. emmae is a distinct molecular species.