Pseudorhabdosynochus inversus sp. nov. (Monogenea, Diplectanidae) from the halfmoon grouper Epinephelus rivulatus (Perciformes, Serranidae) off New Caledonia

Abstract Pseudorhabdosynochus inversus sp. nov. is described from three specimens found in a halfmoon grouper, Epinephelus rivulatus, from the external slope of the barrier reef, New Caledonia, South Pacific. The new species is characterised by the structure of its sclerotised vagina, which resembles that of P. epinepheli (Yamaguti, 1938) but has its primary chamber inverted, and by its measurements. The diplectanid fauna of E. rivulatus shows the same pattern as in other groupers, probably belonging to a clade in which fish species harbour both an abundant species of the ‘Pseudorhabdosynochus cupatus group’ (here P. calathus Hinsinger et Justine, 2006) and a rare species (here P. inversus).