A new species of sole (Pleuronectiformes, Soleidae), Soleichthys labyrinthus, from the China Sea.

The genus Soleichthys (Soleidae) suffers from taxonomic confusion due to morphological similarities. In this study, a new sole species, Soleichthys labyrinthus sp. nov., is described based on the holotype and 24 paratypes collected from the northern South China Sea and the East China Sea. This new species is readily distinguished from its congeners by a unique combination of characters: 78-86 dorsal-fin rays and 65-73 anal-fin rays; the ocular side is tawny brown, featuring a labyrinth-shaped reticulated pattern and lacking the typical transverse bands found in most congeners. The ocular-side lateral line possesses two prominent white spots, accompanied by a series of four (occasionally five) small, longitudinally arranged flaxen-white to light-brown spots occurring along both the dorsal-fin base and the anal-fin base. The caudal fin also bears a broad black transverse band followed posteriorly by a broad white marginal band. Phylogenetic analysis based on the mitochondrial cytochrome c oxidase subunit I (COI) gene robustly supports S. labyrinthus sp. nov. as a distinct monophyletic lineage, while K2P genetic distances reveal deep interspecific divergence (0.182-0.227) from its congeners. This study also provides an updated taxonomic key to all eleven species of Soleichthys.