Cypris Ultrastructure, Metamorphosis and Sex in Seven Families of Parasitic Barnacles (Crustacea: Cirripedia: Rhizocephala)

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Abstract
Cypris morphology in the Rhizocephala differs both between the sexes of individual species and between the species. The large aesthetasc on the third antennular segment is unique to male cyprids of the Lernaeodiscidae, Peltogasteridae and Sacculinidae (suborder Kentrogonida) and Mycetomorpha vancouverensis (suborder Akentrogonida). A fourth segmental aesthetasc, common to both sexes, is much longer in males than in females. A spinous process on the attachment disc is another male‐specific character, but is absent altogether in the Lernaeodiscidae.It is argued that these aesthetascs help locate the settlement targets.Except in Mycetomorpha vancourverensis, aesthetascs have been secondarily lost in cyprids of the suborder Akentrogonida, and there are no other morphological means for separating the male and female settling stage. In cyprids of Sylon hippolytes (Sylonidae) and of Mycetomorpha vancouverensis and Thompsonia sp. (Akentrogonidae) the long and slender antennules are probably used in penetration without formation of a kentrogon, as already reported for Clistosaccus paguri (Clistosaccidae). Cyprids of Sylon hippolytes and Clistosaccus paguri are almost morphologically identical.

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