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contrac- tion into zig-zag folds in one plane; zooids in colonial forms, sharing continuous spasmoneme that runs throughout the entire colony, so that the entire colony is contractile ; some colonial species dimorphic, forming macrozooids, spe- cialized for producing telotrochs or conjugants; oral region as for subclass, but with a retractable peristomial lip and slightly protuberant epistomial disk; macronucleus, band-shaped; micronucleus, present; contractile vacuole, present; cytoproct (?); in marine and freshwater habitats, attached to inanimate objects, plants, rotifers , crustaceans , and even turtles ; eight genera. \u2013 Craspedomyoschiston Precht, 1935 \u2013 Haplocaulus Warren, 1988 \u2013 Mesothamnium Jankowski, 1985 \u2013 Myoschiston Jankowski, 1985 \u2013 Pseudohaplocaulus Warren, 1988 \u2013 Zoothamnioides Schoedel, 2006 * \u2013 Zoothamnium Bory de St. Vincent, 1824 \u2013 Zoothamnopsis Song, 1997 Order Mobilida Kahl, 1933 (syns. Dentodiscida , Mobilia , Mobiliida , Mobilina , Mobilorina , Trichodinina p.p ., Urce olariellina p.p .) Size, medium; shape, conical, cylindrical, or goblet-shaped, sometimes discoidal and orally- aborally flattened; zooid, mobile, comparable to permanent telotroch stage of Order Sessilida, with permanently ciliated trochal band, typi- cally composed of three rings of cilia ; adhesive disk on aboral pole, slightly contractile to ena- ble temporary attachment, its dominant feature being a ring-like, complex skeletal armature of denticles and fibers surrounding a vestigial scopula ; oral region as for subclass, but not contractile; oral structures with infundibular portions of oral polykinetids 1 and 2 always run- ning together in a \u201cribbon\u201d and oral polykinetid 3, short, perpendicular to the other two oral polykinetids ; bacterivorous, obtaining prey from water or from detritus adhering to the host, and microphagous, on cellular debris from host; cysts not observed; in marine and freshwater habitats as ectosymbionts, often on the integument or gills of invertebrates, but other groups, including other cili- ates, amphibians , and fishes , and other locations, 434 17. The Ciliate Taxa Including Families and Genera such as the digestive and urogenital tracts, may also be colonized, sometimes pathogenic in heavy populations; five families. Family LEIOTROCHIDAE Johnston, 1938 Size, medium; shape, cylindrical or barrel- shaped, with slightly bulging apical end and pellicular rings around the body ; adhesive disk with ca . 20 smooth denticles, simple in shape, sur- rounding ciliated scopula; oral ciliature forming a spiral of ca . 400°, with radius equal to that of the adhesive disc ; macronucleus, bulbous with two arms, roughly H-shaped ; micronucleus (?); contractile vacuole, present; cytoproct (?); in marine habitats, widespread as symbionts on the gills of molluscs and on scattered other inverte- brates (e.g., on spines of sea urchins ); one genus. \u2013 Leiotrocha Fabre-Domergue, 1888 (subj. syn. Trichodina ) Family POLYCYCLIDAE Poljansky, 1951 Size, small; shape, conical, tapered apically, with pellicular rings around the body ; adhesive disk with 35\u201360 smooth denticles, densely linked, simple in shape, surrounding scopula with vibratile cilia; trochal band(s), in two distinctly separate girdles ; oral ciliature, deeply invaginated and so relatively inconspicuous, forming a spiral of ca . 360°, with greatly reduced radius ; macronu- cleus, ribbon-like and L-shaped ; micronucleus (?); contractile vacuole (?); cytoproct (?); in marine habitats as endocommensals in the digestive tract of holothurian echinoderms (e.g. Synapta ); one genus. \u2013 Polycycla Polijansky, 1951 Family TRICHODINIDAE Claus, 1874 Size, small; shape, cylindrical, barrel-, or gob- let-shaped, occasionally slightly tapered apically or flattened into discoidal or hemispherical form; adhesive disk with ca . 15\u201360 denticles, complex in shape with a central part with or without an inner spine, and flattened outer blade, often linked to each other by hooks and/or spikes, surrounding a non-ciliated scopula ; oral ciliature, conspicuous, consisting of a spiral ranging from a half-turn of ca . 180° to 2\u20133 nearly full circles, always with a wide radius, equal to that of aboral adhesive disc ; macronucleus, sausage- to horseshoe-shaped; micronucleus, present; contractile vacuole, present; cytoproct (?); in marine and freshwater habitats, widely distributed on a diversity of hosts, such as other ciliates and the integument of various aquatic invertebrates, also on the surfaces of the skin, uri- nary bladder, and especially gills of fishes and a few amphibians , and even the mantle cavity of terrestrial gastropod molluscs ; 11 genera. NOTE : Guhl and Haider (1988) placed Urc- eolaria in this family instead of the Family Urceolariidae. \u2013 Dipartiella G. Stein, 1961 \u2013 Hemitrichodina Basson & Van As, 1989 \u2013 Pallitrichodina Van As & Basson in Aescht, 2001 \u2013 Paratrichodina Lom, 1963 \u2013 Semitrichodina Kazubski, 1958 \u2013 Teretrichodina Jankowksi, 1980 \u2013 Trichodina Ehrenbeg, 1830 \u2013 Trichodinella \u160rámek-Hu\u161ek, 1953 \u2013 Trichodoxa Sirgel, 1983 \u2013 Tripartiella Raabe, 1963 \u2013 Vauchomia Mueller, 1938 Family TRICHODINOPSIDAE Kent, 1881 Size, medium; shape, conical, tapered apically, with pellicular rings; adhesive disk with 30\u201340, smooth denticles, densely linked, surrounding some scopulary cilia and with one trochal band; oral cilia- ture, relatively inconspicuous, consisting of a spiral of ca . 360°, with greatly reduced radius; infundibulum, highly specialized, with bulbous expansion poste- riorly so that the oral ciliature follows a U-shaped, rather than a helical, trajectory, which moves the cytostome into an almost apical position ; macronu- cleus, compact, discoidal; micronucleus (?); contrac- tile vacuole (?); cytoproct (?); in terrestrial habitats as intestinal symbionts of a terrestrial prosobranch snail (e.g. Cyclostoma ); one genus. \u2013 Trichodinopsis Claparède & Lachmann, 1858 (subj. syn. Urceolaria ) Family URCEOLARIIDAE Dujardin, 1840 Size, small to medium; shape, cylindrical, often slightly tipped to one side; adhesive disk with ca. 20, smooth denticles, simple in shape, and with no scopulary cilia ; adoral spiral making a 17.3 The Ciliate Taxa to Genus 435 circuit of ca. 360\u2013400°, with wide radius ; macro- nucleus, discoid or band-shaped; micronucleus, present; contractile vacuole, present; cytoproct (?); in marine and freshwater habitats as ectosymbionts of turbellarians and the gill surfaces of polychaetes and molluscs ; four genera. \u2013 Anthurceolaria Jankowski, 1980 \u2013 Monurceolaria Jankowski, 1980 [not listed in Aescht] \u2013 Orthurceolaria Jankowski, 1980 \u2013 Urceolaria Stein, 1867 Subclass Astomatia Schewiakoff, 1896 (syns. Astomat[e]a , Astom[at]ina ) Size, small to large, often worm-like; shape, cylin- drical or flattened-ovoid; free-swimming, but often attached to host tissues; somatic ciliation, holotri- chous, dense, often with a thigmotactic zone; an infraciliary endoskeleton of considerable complex- ity may be present, frequently with an elaborate, anterior holdfast organelle ; mouthless ; fission, often anisotomic, sometimes catenulate; macronu- cleus, elongate, often extending length of cell; con- tractile vacuoles, often in one or two rows or as a long canal ; cytoproct, absent ; cysts reported in some species; osmotrophic ; in marine, brackish, freshwater, and terrestrial habitats with the majority of species as endosymbionts in the digestive tracts of oligochaetes, but some species in polychaetes , leeches , turbellarians or molluscs , and one major group exclusively in tailed amphibians ; complete life cycle not yet described, but presumed to be direct; one order. NOTE : The monographic works of Cépède