Acanthocercodes n. g. (Monogenoidea: Diplectanidae) for species parasitising threadfins (Perciformes: Polynemidae), with description of Acanthocercodes bullardi n. sp. from the Atlantic threadfin Polydactylus octonemus (Girard) and reassignment of three species of Diplectanum Monticelli, 1903 from the Indo-Pacific Ocean.

Acanthocercodes n. g. (Diplectanidae) is proposed for Acanthocercodes bullardi n. sp. and three previously described species of Diplectanum all parasites of the gill lamellae of threadfins (Perciformes: Polynemidae). The new genus is characterised by species having peduncular spines composed of an anteriorly directed point and a flattened base from which an anterior root arises. Members of the genus lack auxiliary spinous or sucker-like structures in the haptor. Acanthocercodes bullardi n. sp. is described from the Atlantic threadfin, Polydactylus octonemus (Girard), in the Gulf of Mexico off Louisiana, USA. Diplectanum polynemus Tripathi, 1957 is redescribed and transferred to Acanthocercodes as A. polynemus (Tripathi, 1957) n. comb. based on specimens collected from the fourfinger threadfin, Eleutheronema tetradactylum (Shaw), from the mouth of the River Adelaide, Northern Territory, Australia. Diplectanum spinosum (Maillard & Vala, 1980) (=Pseudodiplectanum spinosum Maillard & Vala, 1980) and Diplectanum megacirrus (Maillard & Vala, 1980) (=Pseudodiplectanum megacirrus Maillard & Vala, 1980) from the lesser African threadfin, Galeoides decadactylus (Bloch), are transferred to Acanthocercodes as A. spinosum (Maillard & Vala, 1980) n. comb. and A. megacirrus (Maillard & Vala, 1980) n. comb., respectively.