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over right lateral and ventral surfaces ; somatic extrusomes as rod-shaped mucocysts, not fibrocysts; oral cav- ity, anterior, with three small oral polykinetids and a paroral of reduced size; macronucleus, globular; micronucleus, present; contractile vacuole, present; microphagous; in marine habitats, benthic; two genera. NOTE : This family has been placed here for some time, a placement that requires confirmation by molecular genetic analysis since the ultrastruc- ture of this ciliate shows no clear affinities to other microthoracids. \u2013 Discotricha Tuffrau, 1954 \u2013 Lopezoterenia Foissner, 1997 Family LEPTOPHARYNGIDAE Kahl, 1926 (syns. Pseudomicrothoracidae , Trichoderidae [for Trichopelm(at)idae ]) Size, small; shape, ovoid, slightly flattened; pellicle thrown into obvious cortical ridges, under- lain by well-developed epiplasm; free-swimming; somatic ciliation, holotrichous, but sparse; left border of oral region has perioral somatic kinety of dikinetids and right border has three oral polykinetids ; cyrtos, long, tubular, in ante- rior 1/3 of body ; macronucleus, globular to ellip- soid; micronucleus, present; contractile vacuole, present; microphagous, on bacteria and micro- algae, including cyanobacteria , even filamentous forms; in freshwater and terrestrial habitats, such as mosses; two genera. \u2013 Leptopharynx Mermod, 1914 \u2013 Pseudomicrothorax Mermod, 1914 Family MICROTHORACIDAE Wrzesniowski, 1870 (syns. Conchophryidae , Drepanomonadidae , Trochiliopsidae ) Size, typically very small; shape, crescentic and flattened; free-swimming; somatic ciliation, very sparse, typically with three right preoral somatic kineties, usually of dikinetids, anterior to oral region, and left somatic kineties very reduced ; oral region, variable in position, anterior in some genera (e.g. Stammeridium ) and displaced to the posterior in others (e.g. Microthorax ); typically a reduced paroral and three small oral polykinetids confined to the oral cavity; macronucleus, globular; micronucleus, present; contractile vacuole, present; microphagous; in terrestrial habitats, especially mosses; four genera and two genera incertae sedis . \u2013 Drepanomonas Fresenius, 1858 \u2013 Microthorax Engelmann, 1862 \u2013 Stammeridium Wenzel, 1969 \u2013 Trochiliopsis Penard, 1922 Incertae sedis in Family Microthoracidae \u2013 Conchophrys Chatton, 1911 \u2013 Hexotricha Conn in Conn & Edmondson, 1918 Incertae sedis in Class NASSOPHOREA Order Colpodidiida Foissner, Agatha, & Berger, 2002 Size, small; shape, elongate, ovoid; free- swimming; somatic ciliation, holotrichous, with slight twist to kineties in anterior end; oral region in middle 1/3 of cell, with a paroral and three oral polykinetids that can be reduced in size to only one or two kinetosomes; cytostome- cytopharynx, supported by a delicate cyrtos (?), which extends anteriorly, then dorsally and posteriorly ; stomatogenesis, mixokinetal; macro- nucleus, globular to ellipsoid, may be as two nod- ules; micronucleus, present; contractile vacuole, present; cytoproct, present; feeding on bacteria and flagellates; in terrestrial habitats, particularly saline soils; one family. NOTE : Foissner, Agatha, and Berger (2002) report that their cytological stained preparations suggest the presence of alveolocysts, a diagnostic feature of two orders in the class, and they provide clear evidence for nassophorean features in the stomatogenesis of these forms. The placement of this family requires confirmation by ultrastructural and molecular genetic analyses. Family COLPODIDIIDAE Foissner, 1995 With characteristics of the order; three genera. \u2013 Apocolpodidium Foissner, Agatha, & Berger, 2002 * \u2013 Colpodidium Wilbert, 1982 400 17. The Ciliate Taxa Including Families and Genera \u2013 Pedohymena Foissner, 1995 \u2013 Phagoon Foissner, Agatha, & Berger, 2002 \u2013 Pseudocolpodidium Foissner, Agatha, & Berger, 2002 Class COLPODEA Small & Lynn, 1981 (syns. Bryometopia , Colpodia , Rimostomata p.p ., Transversala p.p ., Stichofragmina p.p .) Size, small to large; shape, variable, but often somewhat twisted; free-swimming with a few species building gelatinous loricae; alveoli, typically well- developed and revealed as a prominent argyrome, typically reticulated ; somatic kineties of dikinetids with a cilium on each kinetosome; somatic diki- netids having one transverse microtubular ribbon and at least one postciliary microtubule associated with the anterior kinetosome, and one transverse ribbon, one postciliary ribbon, and one short kinetodesmal fibril, directed towards the right, associated with the posterior kinetosome; poste- rior transverse ribbons of microtubules extending posteriorly and overlapping one another as the LKm fibre or transversodesma ; parasomal sacs, from two to four, on both sides of kinetid; somatic extrusomes as saccular or rod-shaped mucocysts; oral structures based on a paroral of dikinetids on the right and one to many square-packed polykinetids on the left, but variations from this pattern character- ize included taxa; stomatogenesis, mero- or pleu- rokinetal; fission, often palintomic in a reproductive cyst; macronucleus, homomerous, sometimes with single large nucleolus; conjugation, reported only for bursariomorphids; contractile vacuole, typically posterior, with collecting canals in some larger cells; resting cysts common; feeding, highly variable, with small-sized cells as bacterivores and larger cells as algivores and carnivores; in freshwater and terrestrial habitats, rarely marine; six orders. NOTE : Foissner (1993a) has written an outstand- ing and authoritative monograph on this group. Foissner (1993a, 1994b) has divided this class into the subclasses Colpodia and Bryometopia based primarily on characteristics of the argyrome. The argyrome can be a variable feature of cells, chang- ing with their physiological state. Thus, before we accept this subdivision, we await corroboration of the taxonomic significance of this trait by other kinds of data, such as gene sequences. Order Bryometopida Foissner, 1985 Size, small to large; shape, ovoid; argyrome, \u201ckreyellid type\u201d, a very highly reticulated, subdi- vided dense network ; somatic kineties, slightly spi- ralled; oral region subapical to equatorial with paroral of dikinetids or multiple kinetosomes on right extend- ing to right posterior region of the oral cavity and usually several left oral polykinetids; stomatogenesis, pleurotelokinetal; fission may be in reproductive cyst; four families and one family incertae sedis . NOTE : Foissner (1993a, 1994b) established this taxon based on the character of the argyrome of the included families. We have united these families in this order despite our concerns noted above about the significance of this character to establish a class. The order needs corroboration using other characters. Family BRYOMETOPIDAE Jankowski, 1980 (syn. Thylakidiidae ) Size, small to large; shape, ovoid; free-swim- ming; somatic ciliation, holotrichous, forming a conspicuous postoral suture ; oral region, large relative to body size; paroral typically extending along right border of oral cavity; left serial oral polykinetids conspicuous, typically more than 10, extending along left side of oral cavity ; macronu- cleus, globular to ellipsoid; micronucleus, may be multiple; contractile vacuole, present; cytoproct (?); feeding on bacteria and algae; in freshwater and ter- restrial habitats; two genera. \u2013 Bryometopus Kahl, 1932 \u2013 Thylakidium Schewiakoff, 1893 Family JAROSCHIIDAE Foissner, 1993 Size, small to medium; shape, elongate, ovoid; free-swimming; somatic ciliation, holotrichous; oral region anterior with several differently structured kinetidal elements \u2013 at least includ- ing right kinetofragments, seemingly derived as extensions of somatic