The Anatomy and Sexual Biology of Boschmaella japonica , an Akentrogonid Rhizocephalan Parasite on Barnacles from Japan (Crustacea: Cirripedia: Rhizocephala)

Boschmaella japonica infests the barnacles Chthamalus challengeri and Balanus amphitrite amphitrite . Its morphology is very similar to the previously known members of the family Chthamalophilidae (Rhizocephala, Akentrogonida). Like Boschmaella balani and Bocquelia rosea it has an internal root system within the host. Transmission electron microscopy revealed that the ‘incubatory cavity’ in previous descriptions of the Chthamalophilidae is lined by a thin cuticle, and it is therefore homologous to the mantle cavity found in other Rhizocephala. The development of the male structure resembled events in Chthamalophilus delagei . It is evaginated from the mantle into the mantle cavity as a free‐floating, epithelium‐lined capsule, ‘the spermatogenic island’, which later fragments into numerous secondary spermatogenic islands, where spermatogenesis takes place. Based on new morphological evidence and a comparison with other rhizocephalans, it is suggested that all species of the Chthamalophilidae are gonochorists, in which male cyprids implant spermatogonia directly into the mantle of female externae. The larvae of Boschmaella japonica hatch as cyprids which, like those of other chthamalophilids, lack a thorax and thoracic cirri. This larval feature is thought to be an important factor limiting dispersal of these species. The incidence of multiple‐infested hosts is very high in Boschmaella japonica .