Epiphallus anatomy in theArion hortensisspecies aggregate (Mollusca, Pulmonata)

A SEM study of the structure associated with the outlet of the epiphallus in the atrium genitale of three arionid species ( Arion hortensis s.s., A. distinctus and A. owenii ) is presented. The structures are described and compared, and the specific differences are outlined. Preliminary notes on the same structure in A. intermedius , as well as on the spermatophores of A. hortensis s.s. and A. distinctus , are also provided. It is concluded that A. owenii stands somewhat apart in relation to the latter two species, since it may be more related to A. intermedius. Although it is generally accepted that the genus Arion is characterized by the absence of a penis, it is suggested here that the described structure at the outlet of the epiphallus is nothing but a remnant of an ancestral penis; anyhow, it is at least functionally allied to a penis.