a1 Department of Biology, University of York, PO Box 373, York, YO1 5YW.
a2 Department of Pure and Applied Biology, University of Leeds, Leeds, LS2 9JT
Penis size and morphology of an oviparous species of rough winkle Littorina arcana Hannaford Ellis (Gastropoda: Prosobranchia) was studied at Robin Hoods Bay on the English east coast. Monthly collections were made over a two year period from August 1987 to August 1989 and again from May to December 1993. Number of penial glands was recorded and a six point scale was used to quantify penis maturity. Results indicate that male L. arcana shed their penes in summer and regenerate a new one during the following 12–20 weeks. Male L. arcana in captivity shed penes in July but not in November. The significance of penis shedding and the differences in reproductive seasonality between L. arcana and its ovoviviparous sibling species L. saxatilis is discussed.