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anterior end; free-swimming, typically gliding on the substrate; somatic ciliation on both sides of the body, typically more densely on the right side ; brosse, dorsal, and integrated in one or two dorsolateral kineties; oral region, ventral and elongated, with oral kinetids as left and right components extending along the ventral edge of the laterally flattened body, bordering a vent- or slit-like cytostome, surrounded by toxicysts ; micronucleus lying between two macronuclear nodules ; voracious carnivores; in marine, freshwa- ter, and rarely terrestrial habitats; two families. NOTE : Strüder-Kypke et al. (2006) have con- firmed that this order is monophyletic based on small subunit rRNA gene sequences. However, it emerges from a paraphyletic haptorid clade. Family AMPHILEPTIDAE Bütschli, 1889 Size, small to large; shape, elongate ovoid, often flattened and with narrowing at the anterior and posterior ends; free-swimming, typically gliding on the substrate; somatic ciliation, holotrichous, with right somatic kineties converging on a secant system, the spica, in the anterior middle of the right side ; extrusomes as somatic muco- cysts and oral toxicysts; oral region along ventral \u201cedge\u201d with one right and one left perioral kinety, both composed of dikinetids, border- ing the cytostome ; macronucleus, typically two ellipsoid nodules; micronucleus in between macro- nuclear nodules; contractile vacuole, present; cyto- proct (?); feeding on flagellates and other ciliates, sometimes specializing on peritrich ciliates; in marine and freshwater habitats; seven genera. \u2013 Amphileptiscus Song & Bradbury, 1998 \u2013 Amphileptus Ehrenberg, 1830 372 17. The Ciliate Taxa Including Families and Genera \u2013 Apoamphileptus Lin & Song, 2004 * \u2013 Epiphyllum Lin, Song, & Warren, 2005 * [junior homonym of anthozoan ] \u2013 Kentrophyllum Petz, Song, & Wilbert, 1995 \u2013 Opisthodon Stein, 1859 \u2013 Pseudoamphileptus Foissner, 1983 Family LITONOTIDAE Kent, 1882 (syn. Loxophyllidae ) Size, typically medium to large; shape, flattened ovoid with narrowing at the anterior and posterior ends; free-swimming, typically gliding on the sub- strate; somatic ciliation, holotrichous, with right somatic kineties gradually terminating along rightmost perioral kinety, thus spica absent, and with one or two dorsolateral kineties in some forms ; extrusomes as somatic mucocysts and somatic and/or oral toxicysts, but toxicysts in some forms distributed on the perimeter of the flattened body in protuberances (e.g., Loxophyllum ); oral region along the ventral edge, with two right perioral kine- ties and one left perioral kinety, with rightmost perioral kinety of monokinetids and other kineties of dikinetids ; macronucleus, typically two ellip- soid nodules; micronucleus in between macronuclear nodules; contractile vacuole, present; cytoproct (?); feeding on flagellates and smaller protists; in marine, freshwater, and terrestrial habitats, with some species planktonic; five genera. \u2013 Acineria Dujardin, 1841 \u2013 Heminotus Kahl, 1933 \u2013 Litonotus Wresniowski, 1870 \u2013 Loxophyllum Dujardin, 1841 \u2013 Siroloxophyllum Foissner & Leipe, 1995 Incertae sedis in Subclass Haptoria \u2013 Baznosanuia Tucolesco, 1962 \u2013 Celerita Tucolesco, 1962 \u2013 Racovitzaiella Aescht, 2001 Incertae sedis in Subclass Haptoria Order Cyclotrichiida Jankowski, 1980 (syn. Mesodiniida ) Size, small to medium; shape, globular to sub- spheroid; free-swimming; somatic cilia, bristle-like, of at least two types, arranged in girdles around the body ; brosse kineties absent; extrusomes as oral toxicysts; oral region, apical, domed, circular, and delimited by circumoral dikinetids, but apparently without nematodesmata and bulge microtubules of rhabdos ; macronucleus, ellipsoid to band-shaped; micronucleus, present; contractile vacuole, present; cytoproct (?); feeding on flagellates and microalgae, and sometimes containing symbiotic algae; plank- tonic in marine and freshwater habitats; one family. NOTE : Johnson, Tengs, Oldach, Delwiche, and Stoecker (2004) have demonstrated that the small subunit rRNA sequences of two Mesodinium species are highly divergent to other haptorian sequences, placing them at a basal position in the phylum. Based on the presence of toxicysts and features of the secondary structure of the small subunit rRNA molecule, which suggest homology to the litostomes (see Strüder-Kypke et al., 2006), we are maintaining these ciliates in the Subclass Haptoria until other genes suggest otherwise. Family MESODINIIDAE Jankowski, 1980 With characteristics of the order; four genera. \u2013 Askenasia Blochmann, 1895 \u2013 Mesodinium Stein, 1863 \u2013 Myrionecta Jankowski, 2007 \u2013 Rhabdoaskenasia Krainer & Foissner, 1990 Subclass Trichostomatia Bütschli, 1889 (syn. Synciliostoma p.p .) Size, small to large; shape, ovoid to elongate, some- times with bizarre processes and cell appendages; free-swimming; alveoli, typically well- developed, often filled with \u201cskeletal\u201d material; somatic cilia- tion, variable, from holotrichous to reduced to gir- dles, bands, and tufts, but with somatic kinetids as for the class; concrement vacuole(s) present in a few forms; extrusomes as somatic mucocysts and oral toxicysts absent; oral region or cavity, typically a densely ciliated vestibulum, with oral cilia some- times as \u201cpolykinetids\u201d or syncilia ; cytostome, and therefore vestibulum, sometimes antapical; stoma- togenesis, telokinetal, but cryptotelokinetal in ento- diniomorphids; macronucleus, typically elongate ovoid; micronucleus, present; contractile vacuole, present; cytoproct, often conspicuous; hydrogeno- somes, typically replace mitochondria ; feeding on bacteria, detritus, plant material ingested by the host, and other ciliates; majority of species endocommen- sals in vertebrate hosts; three orders. 17.3 The Ciliate Taxa to Genus 373 Order Vestibuliferida de Puytorac et al., 1974 (syns. Balantidiida p.p ., Balantidiina p.p ., Isotrichida p.p ., Isotrichina p.p ., Infundibuloriina p.p ., Paraisotrichida p.p ., Rimostomata p.p ., Synciliophora s.l ., Vestibulifera s.l .) Somatic ciliation, holotrichous and dense; cortex, often with thick microfilamentous layer between ecto- and endoplasm; oral region a depression or vestibulum, densely ciliated by extensions of somatic kineties, whose cilia do not appear organized as \u201cpolykinetids\u201d ; cytostome at base of vestibular cavity; endocommensals in herbivo- rous placental mammals, but not in marsupials, with balantidiids endocommensals in selected vertebrates from fish to great apes, but parasitic in humans at least ; six families. Family BALANTIDIIDAE Reichenow in Doflein & Reichenow, 1929 (syn. Paranyctotheridae ) Size, small to medium; shape, ovoid to elon- gate; free-swimming; somatic ciliation, holotri- chous, with clavate cilia in several kineties, as possible homologues of the haptorian brosse; no concrement vacuole; extrusomes as somatic muco- cysts; oral cavity apico-ventral, as a vestibu- lar groove less than one-half body length and lined by extensions of somatic kineties, which are accompanied by supernumerary kineties ; macronucleus, elongate ellipsoid; micronucleus, present; contractile vacuole, present; cytoproct, likely absent; encystment probable; feeding on bacteria and organic detritus, but also may feed on host intestinal epithelial cells; in marine, freshwa- ter, and terrestrial habitats as endocommensals in the digestive tracts of diverse hosts, such as insects , fish , frogs , snakes , guinea pig , pig , monkey , chim- panzee , gorilla , and orang-utang , and parasitic at least in man; three genera. \u2013 Balantidium Claparède & Lachmann, 1858 \u2013 Dilleria Earl, 1973 \u2013 Metacollinia Jankowski, 1980 Family ISOTRICHIDAE Bütschli, 1889