Suborder (1) Stichotrichina Fauré-Fremiet, 1961

Body often elongate, sometimes very drawn out posteriorly; ventral cirri generally small and quite inconspicuous (occasionally as few as 2-3 cilia per cirrus) and typically arranged in 3-12 longitudinal (sometimes spiraled) rows; marginals common, transverse cirri sometimes absent; stomatogenesis parakinetal in the allegedly primitive forms studied to date; several species produce loricae, with a few of these exhibiting colony-formation; found free-living in diverse habitats, with one well-known species (Kerona) an ectocommensal on Hydra.

Ventral cirri inconspicuous and in quite numerous and/or helically spiraled rows; zone of adoral membranelles not highly prominent; various body shapes, with some forms tailed and others more elongate at the anterior end; lorica produced by some species; stomatogenesis parakinetal in primitive genera (e.g., Hypotrichidium and Kahliella).	Family SPIROFILIDAE von Gelei, 1929
Elongate forms, with reduced number of spiraled rows of ventral cirri; some species loricate; found in marine, fresh-water, and edaphic habitats.	Family STRONGYLIDIIDAE Fauré-Fremiet, 1961
Ventral cirri in straight rows (of variable number), generally with only transverse cirri (near posterior end) morphologically distinct and conspicuous; body elongate-elliptical in outline, but quite broad, and often of large size (up to 800 µm).	Family UROSTYLIDAE Bütschli, 1889
Right and left marginal cirri present, with variable number of rows of other ventral cirri; transverse and frontal cirri often differentiated; body elongate; macronuclei two to many in number.	Family HOLOSTICHIDAE Fauré-Fremiet, 1961
Cirri long and sparse and in a few curving ventral rows; no differentiated frontals and no transverse cirri; peristomial area limited to anterior third of organism; body oval to elliptical in outline, small, often with zoochlorellae in cytoplasm; two macronuclei; exclusi~aely fresh-water forms.	Family PSILOTRICHIDAE Bütschli, 1889
Cirri relatively uniform, in 7-10 curving ventral rows; body small, rounded-elliptical in outline, with conspicuous peristomial field extending from apical end to well below the equatorial zone of the organism; macronucleus single, marine forms.	Family KIITRICHIDAE Nozawa, 1941
Cirri generally in several oblique rows across the ventral surface of the body; body shape variable, from broad to elongate, even tailed in some species; transverse cirri present; found in various habitats, including sand, and one species well-known ectocommensal on Hydra.	Family KERONIDAE Dujardin, 1840