Cercaria hastatasp. nov. (Digenea: Trematoda) inBullia digitalis, a sandy beach surfing whelk from the Western Cape coast of South Africa: epidemiology and sex linked phenomena

Morphometric and sex linked phenomena in male Bullia digitalis, from the Western Cape coast of South Africa, are related to infection with a digenean microphallid larva described here for the first time and named Cercaria hastata. Penis shedding in Bullia is not uncommon. Most of the stumps are found on infected whelks, and this is probably due to parasitic inhibition of an otherwise rapid regeneration. The infection also abolishes sperm production. Stumps were never seen on sperm producing males, all of which have large penes, and in non-infected males, shedding occurs only in non-producers. In large non-infected Bullia, those which have underdeveloped penes and are non-producers of sperm may be transient intersexes. This is supported by the exhibition of protandry indicators such as brooding, nonsize preferential mate selection and gregariousness. Infection prevalence is size dependent, large whelks being more commonly infected; but parasitic gigantism is thought unlikely as Bullia is iteroparous.