Class II. OLIGOHYMENOPHORA de Puytorac et al., 1974

Syns.

Aspirigera p.p., Aspirotricha p.p., Holotricha [Holotrichasina, Holotrichia] p.p., Kinetodesmatophora p.p., Membranellophora [Membranellata] p.p., Stomatea p.p.; Axotrichidea + Peritrichidea; Hymenotricha (sensu Raabe) + Peritricha; Tetrahymenophora + Cyclohymenophora

Oral apparatus, distinct from the somatic ciliature, comprised of a well-defined paroral membrane plus several membranelles or peniculi typically located in a buccal cavity or infundibulum on the ventral surface of the body, with a cytostome at the base of the cavity (though neither ciliature nor cytostome present in one order); cytopharynx generally inconspicuous; stomatogenesis parakinetal or buccokinetal; kinetodesmata regularly and generally conspicuously present; trichocysts and nematodesmata common in a principal subgroup in which mucocysts are rare; in modes of fission, some (but limited) variation shown; conjugation usually temporary, but solely total in one major group; widely distributed as free-living or symbiotic forms, with many as symphorionts and one entire order endocommensalistic; often microphagous in feeding habits, but the endocommensalistic order entirely osmotrophic.

Buccal structures, when not absent altogether, usually inconspicuous; typically uniform, often heavy, somatic ciliation; body generally of medium size; found in diverse habitats, with nonsymbiotic forms predominantly from fresh-water biotopes.

Subclass (1) Hymenostomata Delage & Hérouard, 1896

Body characteristically inverted bell- or goblet-shaped or conical-cylindrical; conspicuous buccal ciliature, winding counterclockwise, at apical pole and a scopula (plus prominent holdfast derivatives: usually contractile stalk or complex adhesive disc) at antapical pole; somatic ciliature reduced to subequatorial locomotor fringe (trochal band); a ciliated infundibulum into which the contractile vacuole empties, leads to the cytostome; stomatogenesis buccokinetal, with plane of fission of body parallel to major axis; dimorphism (with migratory telotroch stage), colonies, loricae or thecae, and cysts common in the life cycle of many species; conjugation ("total") invariably involves fusion of a micro- with a macroconjugant; very widespread aquatic distribution, with species generally free-living or occurring as symphorionts on diverse hosts, but with some as commensals or even parasites on or in other organisms (ranging from protozoa to vertebrates).

Subclass (2) Peritricha Stein, 1859