Neobythites nanhaiensis sp. nov. (Ophidiidae, Ophidiiformes) from the South China Sea, with morphology, mitogenome, and its phylogenetic position

Neobythites nanhaiensis sp. nov., a new cusk eel species from the South China Sea, is described based on 14 specimens collected at a depth of 400 m near Nan’an Reef. This species is readily distinguished from all congeners by the unique presence of two (rarely three) distinct black ocelli on the mid-flank, a trait absent in all other Neobythites species. It further lacks stripes, fin ocelli, or dark fin margins.

The meristic features include dorsal-fin rays 107 (90–115), anal-fin rays 93 (80–94), pectoral-fin rays 25 (21–27), total vertebrae 62 (58–64), and 9–11 developed gill rakers. The complete mitochondrial genome (17,287 bp) was sequenced, exhibiting the typical vertebrate structure with an A + T bias of 55.1 %. Phylogenetic analyses based on both the COI gene and the complete mitogenome robustly supported N. nanhaiensis sp. nov. as a distinct monophyletic lineage, sister to N. marginatus in the mitogenome phylogeny.

This integrative taxonomic approach, combining morphology, meristics, otolith morphology, and mitogenomic data, confirms the establishment of this new species, which lies outside any existing species group within the genus due to its unique flank ocelli.