There are two genera in cats that are within the subfamily Heterophyinae. The two genera are Heterophyes and Heterophyopsis. Heterophyes is characterized by the possession of a large genital sucker that is separated from the ventral sucker. It was the presence of this "third sucker” that caused Heterophyes to be one of the first genera of trematodes created from the old group the Distoma (two mouths) in the middle of the 1800’s. Heterophyopsis differs from Heterophyes in that its testis lie one behind the other in the body rather than along side each other as they do in the case of Heterophyes.