Rediscovery and elaborate description of

Platycephalus cultellatus Richardson, 1846 was originally found and named in its type locality, Canton, Guangdong Province, China. However, this species was very rare in the coastal waters of China. Except that Qin et al. simply mentioned the original literature records of this species in 2013, no Chinese taxonomy books or publications have ever recorded or described local P. cultellatus. We collected P. cultellatus individuals from the coastal waters of South China Sea and gave valid identification and detailed descriptions of this species. The diacritically meristic counts were listed as follows: first dorsal fin usually with two small isolated spine anteriorly; second dorsal-fin and anal-fin usually with 13 soft rays; pectoral fin usually with 17–19 soft rays and without very small dark spots; caudal fin with 3–6 horizontal blackish bands, but without yellow marking on the middle when fresh; gill rakers 7–10 and pored lateral line scales 65–76. These conclusive characters were consistent with typical P. cultellatus individuals and could thoroughly separate them from other Platycephalus species. The fragment of cytochrome oxidase subunit I (COI) gene of mitochondrial DNA was also sequenced for the classification of specimens. The mean genetic distance within P. cultellatus was 0.25%, net genetic distance between P. cultellatus and other 14 species of the genus Platycephalus ranged from 11.59 to 25.48%. The phylogenetic analysis supported the validity of P. cultellatus existed in the coastal waters of South China Sea. This study will contribute to species identification within this genus distributed in Chinese seas.