Three species of Calydiscoides (Monogenea: Diplectanidae) from five Lethrinus spp. (Lethrinidae: Perciformes) off New Caledonia, with a description of Calydiscoides terpsichore sp. n.

Numerous specimens of Calydiscoides spp. from Lethrinus nebulosus and L. harak, and fewer specimens from L. lentjan, L. ravus and L. obsoletus, collected off New Caledonia, South Pacific, were examined. Three species of Calydiscoides were recognized. Calydiscoides difficilis (Yamaguti, 1953) Young, 1969 was generally the most abundant species on the five hosts. Specimens of C. difficilis were measured and compared to the type specimens (from Indonesia) and museum vouchers (from Australia and the Arabian Gulf). The morphology of the massive male copulatory organ and of haptoral sclerotized parts was similar, but specimens from the same host and from different hosts showed wide morphometric variations; it is concluded that C. difficilis has a high degree of variability, although the possibility of a species complex remains. Calydiscoides duplicostatus (Yamaguti, 1953) Young, 1969 was found on L. nebulosus, L. harak and L. lentjan; specimens were homogeneous in the three hosts and similar to the type specimens. Calydiscoides terpsichore sp. n. is described from L. nebulosus (type host) and L. harak and was uncommon in both fish. The new species, a member of the 'australis group', is characterized by its Y-shaped male copulatory organ, with the left branch bearing a trifurcated secondary branch. Lethrinus nebulosus and L. harak shared the 3 species of Calydiscoides studied here, a fact probably related with their close phylogenetic relationships. Among the 15 species of Lethrinus present in New Caledonia, 11 were examined and 9 species harboured 1-3 species of Calydiscoides each. Only 7 species of Calydiscoides were found, due to their stenoxenous specificity. Each species of Calydiscoides has 1 to 5 hosts.