A study of the anatomy of Pupa and Maxacteon (Acteonidae, Opisthobranchia), with an account of the breeding cycle of Pupa kirki

Summary The external features, mantle cavity, reproductive system and nervous system of Pupa kirki (Hutton, 1873) and three species of Maxacteon Rudman, 1971 are described and compared with Acteon tornatilis (L). It is suggested that the reproductive system of Pupa and Maxacteon, with two accessory sacs, the gametolytic sac and an exogenous sperm sac, is more primitive than that of Acteon tornatilis. The breeding cycle of Pupa kirki shows that the species has a basic annual cycle, a few specimens surviving for two years.