Hermaphroditism in a violet snail, Janthina pallida (Gastropoda, Caenogastropoda): a contribution.

The first data are provided on the gonad development of the violet snail Janthina pallida Thompson, 1840. Histological investigations were carried out on twenty-two specimens cast ashore alive in the Straits of Messina (central Mediterranean). All specimens had an ovotestis with distinct male and female gonads. In large individuals, germinative cells in different stages of spermatogenesis and flagellate spermatozoa were detected, together with oocytes in different stages of oogenesis and mature oocytes; in small specimens only immature male and female gonads were observed. No specimens of intermediate size were found. Simultaneous rather than size-related hermaphroditism in J. pallida contrasts with the current view of protandric hermaphroditism as a common trait in Janthina genus, instead suggesting a changing reproductive pattern, driven by population density and food availability.