Larval development and complemental males in Chelonibia testudinaria, a barnacle commensal with sea turtles

That some barnacles are obligate commensals of sea turtles has long been known; however, little attention has focused on understanding the details of this association. In particular, early life-history traits of turtle barnacles, which may be key to establishing the association, have not been well studied. Here we present the first complete description of larval development in a turtle barnacle. Embryos were collected from Chelonibia testudinaria, a cosmopolitan and conspicuous species, and reared through metamorphosis in the laboratory. We followed sequential molting and described each stage using light microscopy. Development proceeded over nine days at 25degreesC and the characteristic cirriped pattern of six naupliar stages followed by a cyprid larva was observed. Implications for the association of barnacles with sea turtles are discussed relative to spatio-temporal aspects of cyprid attachment and the life history of sea turtles. Barnacle reproduction typically involves cross-fertilization between hermaphrodites but small complemental males occur in some species. In C. testudinaria, small individuals attached to hermaphrodites were confirmed to be exclusively male. They were located in the external depressions between the shell plates of hermaphrodites, within pits perhaps specialized for their settlement. This attachment location, external to and below the orifice of the hermaphrodite shell, is unique for complemental males. It is not known whether the males of C. testudinaria remain small permanently or eventually grow to become hermaphroditic, as do protandric complemental males in C. patula. Their small size may provide advantages in reducing drag and their attachment location may afford protection from removal.