The Digenea of the Intertidal Prosobranch, Littorina Saxatilis (Olivi)

A description is given of the rediae or sporocysts, cercariae and, where known, metacercariae, encystment, ecology and host specificity of the larval digenean parasites of the subspecies and varieties of Littorina saxatilis (Olivi), mainly in Britain. The parasites are Microphallus similis (Jaegerskioeld, 1900) (=C. ubiquita Lebour, 1907; C. ubiquitoides Stunkard, 1932; Cercaria sp. Rees, 1936a), Cercaria littorinae saxatilis I, II, III & IV spp. nov. (Microphallidae), Cercaria lebouri Stunkard, 1932, Parapronocephalum symmetricum Belopolskaia, 1952 (Notocotyloidea), Cercaria emasculans Pelseneer, 1906, Cercaria brevicauda Pelseneer, 1906, Cercaria roscovita Stunkard, 1932 (Plagiorchioidea) and Podocotyle atomon (Rud., 1802) (Opecoelidae). Observations are included on the life cycle of Microphallus similis, on the histochemistry of some of the species and on the incidence of double and triple infections.