Journal of the Marine Biological Association of the United Kingdom

Research Article

Shell Shape Variation in Littorina Saxatilis and L. Arcana: A Case of Character Displacement?

J. Grahamea1 and P.J. Milla1

a1 Department of Pure and Applied Biology, University of Leeds, Leeds, LS2 9JT

It is now well established that there are several species in the group of rough periwinkles inhabiting European rocky shores. The usual consensus agrees on four, namely Littorina saxatilis (Olivi), Littorina arcana Ellis, Littorina nigrolineata Gray and Littorina neglecta Bean. The first two species are particularly difficult to distinguish in the field and have received much attention. Recent work indicates that the ovoviviparous L.saxatilis is a very variable species living in a wide range of habitats (e.g. Janson, 1985) and that, although it is close to the oviparous L. arcana in shell morphology and in genotype, the two are separate species (Ward & Warwick, 1980; Ward & Janson, 1985), and not reproductive morphs of the same species.