Hymenolepididae

The Hymenolepididae are family of cyclophyllid tapeworms. Their characteristic feature is the small number of testes (one to four). The unilateral genital pores and large external seminal vesicle allow for easy recognition. Most species are small, transparent, and easy to study. The family contains over 90 genera with over 900 species, having as their definitive host birds (c. 700 species) or mammals (about 250 species). Most reside in the intestines of their definitive hosts. The majority of species with known lifecycles have arthropods as intermediate hosts.