HAPLORCHIINAE
This subfamily of Heterophyids is characterized by the possession of a single testis, although one of the genera in this family, Stellantchasmus, actually has two testes. There are three genera within this subfamily, Haplorchis, Procerovum, and Stellantchasmus. Procerovum specimens differ from those of Haplorchis is that they possess a highly muscular ejaculatory duct called an "expulsor." Stellantchasmus specimens differ from those of Haplorchis and Procerovum in that they possess two testes while possessing an expulsor as in Procerovum.