Periwinkles and parasites: the occurrence and phenotypic effects of parasites inLittorina saxatilisandL. arcanain northeastern England

Littorina saxatilis is a common intertidal gastropod on shores of the North Atlantic, and an 24 important study species for evolutionary investigations. Its congener L. arcana is much less 25 widely distributed, but both species are common at Old Peak, Yorkshire, UK. The parasite 26 profiles of L. saxatilis and L. arcana from this shore were determined histologically, revealing 27 a ciliated protist, Protophrya ovicola, an unidentified apicomplexan (present in