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Phylum C I L I O P H O R A Doflein, 1901

Eukaryotic, unicellular, heterotrophic protists (size 10 - 4500 µm), free-swimming or sessile, with cilia (simple or compound) in at least one stage of life cycle;

complex cortical infraciliature, somatic plus often oral;

pellicular alveoli;

microtubular or microfibrillar structures, often kinetosome-associated, and extrusomes common;

fission homothetogenic and often perkinetal, isotomic or anisotomic, and occasionally multiple;

nuclear dualism (rare exceptions), one or more diploid micro- and one to several polyploid (rarely diploid or oligoploid) macronuclei, with acentric mitosis and "gametic" meiosis;

conjugation, temporary or total, widespread;

generally monostomic, but some groups mouthless or polystomic;

contractile vacuole typically present, often also a cytoproct;

feeding modes: osmotrophy to phagotrophy;

broad distribution, diverse aquatic and edaphic habitats, with ecto- or endosymbiosis exhibited by a number of species.

Oral ciliature, of kinetofragments, basically circumoral, atrial, or vestibular in position and nature (when present at all); cytostome frequently apical or near-apical, directly on surface of body (polar or ventral) or preceded by a vestibulum; one group polystomic (suctorial tentacles); cytopharyngeal apparatus, as found in most major groups, is either a rhabdos or a cyrtos (each with prominent nematodesmata), typically conspicuous; stomatogenesis fundamentally telokinetal, though apokinetal in one major group; many species with toxicysts, some with kinetodesmata, a few with trichocysts, and one whole group with postciliodesmata; generally rypical nuclear dualism, but one group homokaryotic and a second with dependent, diploid macronuclei; modes of fission include budding or other bizarre rypes in a number of species; conjugation is usually temporary, but total in many members of two groups; widespread in diverse habitats, free-living to endoparasitic; often carnivorous in feeding habit.	Class I. KINETOFRAGMINOPHORA de Puytorac et al., 1974
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.	Class II. OLIGOHYMENOPHORA de Puytorac et al., 1974
Oral ciliature conspicuous, with adoral zone of multiple membranelles (generally paramembranelles) especially prominent and often extending out of buccal cavity onto and/or around anterior end of body; one or more paroral membranes on the right; paucity of simple somatic ciliature (except in one major group) or with its replacement by cirri (in another group); stomatogenesis parakinetal or apokinetal; kinetodesmata rare, toxicysts and trichocysts absent; postciliodesmata common and prominent; fission almost always isotomic; conjugation temporary and isogamontic; species widely distributed, generally of large body size and diverse feeding habits, and (with one or two subgroup exceptions) very commonly free-living, free-swimming forms.	Class III. POLYHYMENOPHORA Jankowski, 1967