Abstract: Based on cytochrome oxidase subunit I (COI) barcoding marker of 33 flatfishes in the subfamily Cynoglossinae of Pleuronectiformes, the molecular phylogenetic trees were constructed by maximum likelihood and Bayesian inference method for the Cynoglossusphylogenetic analysis. The results showed that fishes of Cynoglossinae are one monophyletic group, which has a stable sister-group relationship with Symphurinae. In the taxa of this study, fishes of Paraplagusiaclustered into a shallow branch, forming a late specialization group of Tongue soles. The genus Cynoglossuswas divided into eight main branches. Species composition of these eight branches differs from that in the classification system based mainly on morphological characters, including numbers of lateral lines and nostrils. The species in four branches were similar to four groups (canariensis, heterolepis, arel, and cynoglossus) out of the six from Menon’s system based on the morphological characteristics, while the kopsii group showed a great difference in branches classification. In addition, the K2P genetic distances among the eight branches of Cynoglossuswere bigger than those in Paraplagusiasubgenus, which indicates a further split among species or subgenus. The data of K2P genetic distance analysis also revealed that the Cynoglossus lightiNorman is a junior synonym of Cynoglossus joneriGünther, and that Cynoglossus purpureomaculatusRegan is a junior synonym of Cynoglossus abbreviatus(Gray).

Key words: Pleuronectiformes, Cynoglossus, Paraplagusia, K2P genetic distance, synonym