Pseudorhabdosynochus argus n. sp. (Monogenea: Diplectanidae) from Cephalopholis argus, P. minutus n. sp. and Diplectanum nanus n. sp. from C. sonnerati and other monogeneans from Cephalopholis spp. (Perciformes: Serranidae) off Australia and New Caledonia.

Monogeneans from three species of Cephalopholis, namely C. argus, C. sonnerati and C. boenak, are described from fish caught off New Caledonia, South Pacific, with comparisons with material from off Queensland, Australia. Pseudorhabdosynochus argus n. sp. from C. argus is present off New Caledonia and Australia; it is characterised by its male quadriloculate organ with very elongate cone, and its sclerotised vagina with anterior trumpet, coiled primary canal and distal part with two chambers and an accessory part. C. boenak has no monogeneans off New Caledonia, but off Australia it harbours Pseudorhabdosynochus sp., a new species which is morphologically related to P. argus. P. minutus n. sp. from C. sonnerati is characterised by its minute body and a sclerotised vagina with two spherical chambers. Diplectanum nanus n. sp. from C. sonnerati is characterised by its very small funnel-shaped male copulatory organ and minute body. A new species, Haliotrema sp. from C. sonnerati is characterised by a very elongate tubular penis; it is distinct from H. cromileptis Young, 1968 (redescribed herein from specimens collected from Cromileptes altivelis off New Caledonia). The species described here include the first members of Pseudorhabdosynochus and the first diplectanids described from species of Cephalopholis. There is no evidence for a clade of Pseudorhabdosynochus species specific to members of Cephalopholis, since the species described here share similarities with other species from Epinephelus. However, it is suggested that the gill structure of Cephalopholis spp. imposes selection toward small body sizes for monogeneans.