The Mesocestoididae are parasites in the small intestine of mammals, rarely birds (Rausch, 1994). Two genera, Mesocestoides and Mesogyna, are recognized within this family. The adult is characterized mainly by the possession of a scolex that bears four muscular suckers, but no rostellum, and segments that contain medial sexual openings. In the mature proglottid, the eggs are contained in a single thick-walled parauterine organ. The life cycle of the members of this family are not known, but what is known based on our knowledge of Mesocestoides is that it appears that there are two intermediate hosts in the life cycle. The first intermediate host has been assumed to be an arthropod. The second intermediate host can be a reptile or small mammal that contain a larval stage, called a tetrathyridium, which is a solid-bodied larva that has a scolex similar to that of the adult worm. Cats can serve as the final host for Mesocestoides in which case the adult worms are present in the small intestine. Cats can also be infected with the tetrathyridial stage of this parasite.
Rausch RL. 1994. family Mesocestoididae Fuhrmann, 1907. In: Keys to the Cestode Parasites of Vertebrates, Khalil LF, Jones a, Bray RA, eds. CAB International, Wallingford, UK.