Pseudophyllidea

Pseudophyllidean tapeworms have a scolex with four longitudinal grooves. They have a genital pore which is centrally placed on each segment. The eggs and life-cycle have some similarity to that of the trematodes. Pseudophyllidean egg shell is thick, brown and operculate. The Pseudophyllidean life-cycle uses two intermediate hosts – the coracidium, which emerges after hatching, must first be ingested by a crustacean. A larval procercoid develops within the body cavity of the crustacean. If the crustacean is then eaten by a freshwater fish, the procercoid is liberated and develops into a second larval stage, a plerocercoid, within the muscles of this new host. The plerocercoid possesses the characteristic scolex – it is only this stage that is infective to the final host. There are no pseudophyllideans of importance in the UK, but some are of significance in tropical or sub-tropical areas (for example Spirometra), and in sub-arctic regions (for example Diphyllobothrium).