Stein, 1859
With characteristics of order. Somatic ciliature well developed, adoral membranelles numerous and prominent. Body large, often contractile. Single conspicuous contractile vacuole in posterior end of body. Mucocysts abundant, pigment vesicles common in many species. No loricae, cysts common. Free-living, widely distributed.
Family Spirostomidae
Family Condylostomatidae
Family Stentoridae
Family Peritromidae