These are common parasites of fishes and other poikilotherms, but occasionally are associated with pathology.
Definitive hosts include fish, amphibians and reptiles. Eggs shed in water release a coracidium which is ingested by a crustacean first intermediate host. There the parasite develops into a procercoid which is infective to a second intermediate host poikilotherm. The parasite develops into a plerocercoid, which is infective to the definitive host.
The scolex is simple, with four lateral suckers and occasionally an apical sucker. There are numerous testes and the vitellaria occur in lateral fields. Genital pores are lateral.