Morphology of developmental stages of Caligus clemensi (Copepoda: Caligoida), a parasite of important commercial fish species, is described. The development cycle consists of two nauplius stages, one copepodid, four chalimus stages, and one preadult. This cycle is compared with ontogeny of five other species of Caligidae. The author concludes that one preadult stage has been missed in the cycle of C. clemensi and that evidence so far available points to existence of a ten-stage cycle of development, including two preadult stages and the adult.