The Pseudophyllidea is a group of tapeworms whose adults are most commonly found in fish. The group is characterized by having a scolex that usually is armed with two bothria, slits on the dorsal and ventral aspect. The genital pores in this group are located medially on each segment. The majority of genera in this order are found in fish, but one family, the Diphyllobothriidae is found mainly as adults in reptiles, birds, and mammals (such as whales, cetaceans, and pinnipeds). The typical life cycle involves a crustacean as the first-intermediate host and a fish as the second intermediate host. Cats are hosts to two genera of these parasites in the adult stage, Diphyllobothrium and Spirometra. Diphyllobothrium is found as adults in fish-eating birds and mammals. Spirometra differs from Diphyllobothrium in that the second intermediate host tends to be a terrestrial or semi-terrestrial vertebrate, and the adults are mainly in cat-like carnivores.