Abstract
The present study describes and illustrates the morphology of naupliar and copepodid stages of Caligus sclerotinosus Roubal, Armitage and Rohde, 1983 (Copepoda: Siphonostomatoida: Caligoida), an invasive, non-indigenous parasite collected from commercially important red sea bream Pagrus major (Temminck and Schlegel, 1843) (Sparidae) cultured as well as wild populations in western Japan. The life cycle of C. sclerotinosus consists of 8 stages: two nauplii, five copepodids (copepodid I to V) and one adult, which exhibited the general pattern of other congeners. Sexual dimorphism was first observed in the urosome and antenna of copepodid IV. The body lengths of the developmental stages of 14 Caligus spp. are compared to those of C. sclerotinosus. The oral cone of copepodid I is highly unique for its suckerlike shape, widely expanded terminally. All post-naupliar stages were found on the same host fish P. major, rejecting the previous hypothesis for the presence of intermediate hosts for the development of C. sclerotinosus.