Size and settling behaviour in male and female cypris larvae of the parasitic barnacle Sacculina carcini Thompson (Crustacea: Cirripedia: Rhizocephala)

Twenty-one broods from different externae of Sacculina carcini Thompson were cultured to the cypris stage. The size of the cyprids was measured and the larvae subjected to settling upon unparasitized crabs (Garcinus maenas (L.)) and small juvenile externae. The cyprids occur in two sizes that may appear singly or together in the same brood. Small cyprids are of the female sex that settle upon crabs and are infective, while large cyprids are of the male sex and only settle upon juvenile externae. These results are in agreement with other well-studied rhizocephalans.