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shallow depression; oral polykinetids reduced, with oral polykinetid 1 typically non-ciliated and with relatively inconspicuous oral ciliature on the other two oral polykinetids ; scutica, a trian- gular arrangement of ciliated kinetosomes in the director meridian ; macronucleus, globular to ellipsoid; micronucleus, present; contractile vacuole, present; cytoproct, present; bacterivorous; in marine, freshwater, and occasionally terrestrial habitats; seven genera. \u2013 Homalogastra Kahl, 1926 \u2013 Pseuduronema Hoare, 1927 \u2013 Urocyclon Song & Wilbert, 2000 \u2013 Uronema Dujardin, 1841 \u2013 Uronemella Song & Wilbert, 2002 * \u2013 Uronemopsis Kahl, 1931 \u2013 Uropedalium Kahl, 1928 Family UROZONIDAE Grolière, 1975 (syn. Urozonatidae ) Size, very small; shape, ovoid, but well rounded at anterior and posterior ends ; free-swimming; somatic ciliation as a series of short kineties, forming a single equatorial belt of somatic ciliature; caudal cilium, single, long; oral region as deep equatorial cavity with two oral polyki- netids of two rows of kinetosomes, transverse to the longitudinal axis of the oral region ; scu- tica of several kinetosomes in \u201cV\u201d configuration; macronucleus, globular; micronucleus, present; contractile vacuole, present; cytoproct, present; bacterivorous; in freshwater polysaprobic habitats; one genus. \u2013 Urozona Schewiakoff, 1889 Incertae sedis in Order Philasterida \u2013 Andreula Kahl, 1934 \u2013 Bizonula Corliss, 1960 \u2013 Cryptostomina Fedele, 1938 \u2013 Eurychilum André, 1910 \u2013 Lembadionella Kahl, 1933 \u2013 Ptyssostoma Hentschel, 1927 \u2013 Pusilloburius Corliss, 1979 \u2013 Rhinodisculus Mansfeld, 1923 \u2013 Sertumia Tucolesco, 1962 Order Pleuronematida Fauré-Fremiet in Corliss, 1956 (syns. Conchophthiriina p.p ., Deuterostomatina p.p ., Pleuronematorina ) Size, very small to medium, with occasional striking exceptions; shape, ovoid; free-swimming, but with some forms restricted to loricae; somatic ciliation, holotrichous, but often more sparse posteriorly, with thigmotactic ciliation often well developed in some taxa; caudal cilia, typically one or more, conspicuous in many species; extru- somes as somatic mucocysts, sometimes of two types, one being rod-like; oral region, often expansive, with paroral often prominent with long cilia, forming a curtain or velum as the organism feeds; paroral infraciliary base with a short a and an elongate b segment and with c segment as a permanent scutica or scuti- covestige; ribbed wall conspicuous, may be in two fields ; cytostome, equatorial or subequatorial in anterior 3/4 of body, rarely leaving room for a director-meridian; stomatogenesis of opisthe oral structures derived from paroral of proter and scutica ; microphagous, predominantly bacte- rivorous, but some species algivorous; in marine, freshwater, and terrestrial habitats, widely distrib- uted as free-living forms, sometimes in sands, but with some species commensalistic in molluscs and other invertebrates, and some species coprozoic; nine families. 17.3 The Ciliate Taxa to Genus 419 Family CALYPTOTRICHIDAE Small & Lynn, 1985 Size, small; shape, elongate ovoid; free-swim- ming, but residing in a tubular lorica ; somatic ciliation, holotrichous, dense; caudal cilium, present; oral region occupying most of ven- tral surface with conspicuous velum, extending around posterior of oral region and onto its left posterior margin, and with oral polykinetid 1 relatively longer and narrower than oral polyki- netid 2 ; cytostome, postequatorial; macronucleus, globular; micronucleus (?); contractile vacuole, present; cytoproct (?); bacterivorous; in brackish and freshwater habitats; one genus. \u2013 Calyptotricha Phillips, 1882 Family CONCHOPHTHIRIDAE Kahl in Doflein & Reichenow, 1929 (syn. Conchophthiriidae ) Size, small to medium; shape, generally ellipsoi- dal to broadly reniform, laterally compressed; free- swimming; somatic ciliation, holotrichous, dense; caudal cilia, may be present, sometimes long; thigmotactic ciliature on right anterior as field of structurally differentiated ciliated somatic dikinetids; oral region, nearly equatorial, as relatively small cavity into which vestibular kineties may extend on its right or left side; oral polykinetids reduced, obliquely oriented along left anterior wall of oral cavity; germinal row of stomatogenic kinetosomes deep in oral cavity ; macronucleus, globular to ellipsoid, rarely nodular; micronucleus, present; contractile vacuole, present; cytoproct, present; bacterivorous and detritivorous; in freshwater habitats as endocommensals in the mantle cavity (on gills) of bivalve molluscs ; two genera. \u2013 Conchophthirus Stein, 1861 \u2013 Conchoscutum Raabe, 1947 Family CTEDOCTEMATIDAE Small & Lynn, 1985 Size, small; shape, ovoid; free-swimming; somatic ciliation, holotrichous, sparse, typically of ciliated dikinetids; caudal cilia, prominent; oral region, midventral with cytostome posterior to equator; velum of paroral segments a , b , and c , comb-like, as an open \u201cC\u201d, not extending to the left of the cytostome ; ribbed wall, conspicuous ; oral polykinetid 3 at right angle to longitudinal axis of oral region ; macronucleus, globular to ellipsoid, rarely nodular; micronucleus, present; contractile vacuole, present; cytoproct, present; bacterivorous; in marine habitats; five genera. \u2013 Compsosomella Small & Lynn, 1985 \u2013 Ctedoctema Stokes, 1884 \u2013 Hippocomos Czapik & Jordan, 1977 \u2013 Paractedectema Small & Lynn, 1985 \u2013 Paractedoctema Song & Wilbert, 2000 Family CYCLIDIIDAE Ehrenberg, 1838 Size, very small to small; shape, ovoid to elongate- ovoid, often with glabrous anterior and posterior zones; free-swimming; somatic ciliation, hol- otrichous, sparse, but denser in the anterior half of the body in some genera; caudal cilium, distinctive, one to several ; oral region, not promi- nent, with cytostome variable in position and oral ciliature not conspicuous; paroral dikinetid, often inconspicuous, typically with its postcytostomal curve not extending anterior and left of cyto- stome ; oral polykinetids, often highly fragmented; macronucleus, globular to ellipsoid; micronucleus, large, often located in anterior third of body; contractile vacuole, present; cytoproct, present; bacterivorous; in marine, brackish, freshwater, and terrestrial habitats, widely distributed with intersti- tial, anaerobic, and coprozoic species; ten genera. \u2013 Apocyclidium Foissner, Agatha, & Berger, 2002 * \u2013 Caspionella Jankowski, 1980 \u2013 Cristigera Roux, 1899 \u2013 Cyclidium O.F. Müller, 1773 \u2013 Echinocyclidium Jankowski, 1980 \u2013 Isocyclidium Esteban, Finlay, & Embley, 1993 \u2013 Mesogymnus Berger in Corliss, 1979 [ nomen nudum ] \u2013 Paracyclidium Grolière, de Puytorac, & Grain, 1980 \u2013 Protocyclidium Alekperov, 1993 \u2013 Pseudocyclidium Small & Lynn, 1985 Family DRAGESCOIDAE Jankowski, 1980 Size, small; shape, ovoid, flattened; free- swimming; somatic ciliation, uneven, with 420 17. The Ciliate Taxa Including Families and Genera several close-set thigmotactic kineties along right-ventral anterolateral margin; oral region, midventral, with single oral polykinetid, which runs adjacent to the inside curve of the paroral and which is presumably a fusion of three oral polykinetids ; macronucleus, ellipsoid; micronu- cleus, present; contractile vacuole, present; cyto- proct, present; bacterivorous(?); in marine habitats as ectosymbionts on certain strongylocentrid echi- noids ; one genus. \u2013 Dragescoa Jankowski, 1974 Family HISTIOBALANTIIDAE de Puytorac & Corliss in Corliss, 1979 (syns. Sulciferiidae , Sulcigeridae ) Size, medium to large; shape, elliptical in out- line, with right side slightly concave and anterior end a little narrower than posterior; free-swim- ming; somatic ciliation, holotrichous,