This study recognises four species of
Diopatra Audouin and Milne Edwards from Thailand. A key is provided.
Diopatra amboinensis Audouin and Milne Edwards, 1833 and
D. sugokai Izuka, 1907 are widely distributed in the Indo-Pacific region.
Diopatra claparedii Grube, 1878, is redescribed, with
D. bulohensis Tan and Chou, 1996 as its new junior synonym.
Diopatra neapolitana khargiana Wesenberg-Lund, 1949 is elevated to specific rank and redescribed, with
D. bengalensis Hartman, 1974 as its new junior synonym.
Diopatra semperi Grube, 1878, although not known to occur in Thailand, is redescribed to clarify its confusion with
D. claparedii.