Suborder (1) Tetrahymenina Fauré-Fremiet in Corliss, 1956

Syn.	Tetrahymenorina

With the more conservative characteristics of the order (above). Relatively inconspicuous "UM + AZM" mouthparts, generally, and one family secondarily mouthless; stomatogenesis parakinetal; preoral but no postoral suture; mucocysts common, but no trichocysts or oral nematodesmata; widespread fresh-water microphagous forms (a few edaphic and/or histophagous, and several polymorphic with carnivorous macrostome stage) plus some symbiotic species, latter (whether facultative or obligate forms) associated mainly with invertebrate hosts.

With general characteristics of suborder s.s. (above); body pyriform to elongate-ovoid to cylindrical in shape; membranellar bases of uniform width; one to three (up to nine in Lambornella) postoral kineties, rightmost one typically stomatogenic; some species with caudal cilium; members of one genus (Tetrahymena) unique in exhibiting polymorphism (microstome-macrostome stages, cysts, etc.) and (endo)symbiosis in variety of hosts (slugs, snails, clams, enchytraeid worms, midges, mosquitoes, tadpoles, fishes, etc.); fresh-water or edaphic habitats.	Family TETRAHYMENIDAE Corliss, 1952
Body ovoid to ellipsoidal; buccal cavity large; infraciliary base of second or third membranelle much wider (in rows of kinetosomes) than others; 5-10 postoral kineties, rightmost one stomatogenic; no caudal cilia; all species free-living, generally microphagous; fresh-water, occasionally edaphic, habitats.	Family GLAUCOMIDAE Corliss, 1971
Large body, elongate-ovoid (tapering posteriorly) in shape, with conspicuous oral structures in anterior half; buccal ciliature comprised of membranelles resembling peniculi and quadrulus, yet stomatogenesis parakinetal, as in the Glaucomidae; somatic ciliature, including several postoral kineties, typically tetrahymenine; no nematodesmata nor trichocysts, but also no mucocysts; dimorphic life cycle, with macrostome form carnivorous on other ciliates; fresh-water habitats.	Family TURANIELLIDAE Didier, 1971
Mouthless forms; body small, pyriform to ovoid in shape; silverline system much like that of Tetrahymena (family Tetrahymenidae, above); obligate endosymbiont in tissues or cavities of fresh-water snails, limpets, clams, and turbellarians.	Family CURIMOSTOMATIDAE Jankowski, 1968
Conspicuous buccal ciliature of unknown composition, apically located; small body size, with sparse somatic ciliation plus caudal cilium; found in soil.	Family SAGITTARIIDAE R. & L. Grandori, 1935