The ultrastructure of the integument in a parasitic copepod Ophioika sp., which may be a new species, is described using SEM and TEM of specimens both in situ and dissected out of their brittlestar host, Ophiocoma scolopendrina. The parasite is found embedded in host connective tissue at the base of the arm. The surface of the parasite's integument facing the host has knob-like projections, some of which have long microvilli-like endings. Whether these structures have an absorptive function and play a role in the parasite's feeding is discussed.