The occurrence of larval Digenea in ten species of intertidal prosobranch molluscs in Cardigan Bay

Summary The percentage infection with fifteen species of larval Digenea is described in ten species of littoral prosobranchs in Cardigan Bay. In some host species percentage infection varies with the position on the shore in relation to the height above chart datum and to exposure to wave action. These variations are attributed, partly to the behaviour of the host species, to the effects of environmental conditions on the susceptibility to infection of the first intermediate host and on the free-living stages of the parasite and to the physiological or genetical resistance of the first intermediate host.