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& Katz, 2001) while trees based on large subunit rRNA gene sequences place the colpodeans near to nassophoreans and oligohymenophoreans (Baroin- Tourancheau, Villalobo, Tsao, Torres, & Pearlman, 1998). Histone gene sequences (Bernhard & Schlegel, 1998) and \u3b1-tubulin nucleotide sequences (Baroin-Tourancheau et al., 1998) support this latter relationship. Foissner (1993a, 1994b) recognized two sub- classes, the Subclass Colpodia and Subclass Bryometopia , based primarily on features of the reticulate silverline system . There are three gen- eral types of silverline systems in the colpodeans : the colpodid , platyophryid , and kreyellid patterns. Foissner (1978) demonstrated the usefulness of the silverline system in identifying relationships among colpodeans . However, as shown many years ago by Taylor and Garnjobst (1939) and confirmed by Foissner (1993a, 1994b), the silverline system is a dynamic element of the cortex, even changing from one type to another within the same species! Thus, we are reluctant at this time to support the subclass taxa based only on this feature and will await gene sequence data to confirm this fundamental divi- son within the class. We currently recognize six orders in the class: Bryometopida , Bryophryida , Bursariomorphida , Colpodida , Cyrtolophosidida , and Sorogenida , based mainly on the monographic work of Foissner (1993a). The Order Bryometopida is characterized as hav- ing an argyrome with a very highly reticulated and subdivided dense network (i.e., \u201ckreyellid type\u201d , Foissner, 1993a). Oral structures include typi- cally a paroral of dikinetids, sometimes modified, and several left oral polykinetids. There are four families in the order: Bryometopidae , Jaroschiidae , Kreyellidae , and Trihymenidae . The Order Bryophryida , monotypic for the Family Bryophryidae , is characterized by right oral kineties that at least include a series of radially oriented kinetosomal rows, except for the genus Notoxoma , in which these are interpreted to have been reduced to dikinetids. There can be a single or multiple left adoral polykinetids composed of square-packed kinetosomes (Foissner, 1993a). The Order Bursariomorphida , which includes the Families Bursariidae and Bursaridiidae , is charac- terized by an expansive oral cavity whose left side is lined by many, long and equidistantly spaced oral polykinetids (Fernández-Galiano, 1979; Foissner, 1993a). These oral polykinetids are typically of two to three rows of kinetosomes, arranged in a square-packed arrangement. The right oral ciliature is composed of many regularly or slightly irregu- larly and obliquely arranged \u201cparoral\u201d kineties. The Order Colpodida includes colpodeans that undergo merotelokinetal stomatogenesis , developing a left oral polykinetid that is composed of several to many rows of regularly-spaced monokinetids. Foissner (1993a) recognized the monotypic Order Grossglockneriida as distinct from the Order Colpodida . However, the similarities in stoma- togenesis and general morphology strongly suggest affinities between the two, whose genera are not greatly different based on SSUrRNA gene sequences (Lynn et al., 1999). In addition to the Family Grossglockneriidae , we also include the following families: Colpididae, Hausmanniellidae , Marynidae , Bardeliellidae , and Grandoriidae . Of the remaining orders recognized by Foissner (1993a, 1994b), this leaves the Cyrtolophosidida and Sorogenida . Lasek-Nesselquist and Katz (2001) have noted the strong genetic similarities in SSUrRNA gene sequences between Sorogena , the only representative for the Order Sorogenida , and those of the cyrtolophosidid Platyophrya . They recommended suppression of the Order Sorogenida , which is considered distinct primarily on the basis of the unusual sorocarp development in the life cycle of its type genus (Foissner, 1993a). Furthermore, the stomatogenesis of Sorogena appears to be similar to that of Platyophrya and other cyrtolophosidids (Bardele et al., 1991). However, we have maintained this order, monotypic for the Family Sorogenidae , until a more complete analysis of molecular genetic diversity compels us to suppress it. Finally, taxa in the Order Cyrtolophosidida show strong similarities in stomatogenesis to bryome- topids , like Bryometopus (cf., Dragesco, Fryd- Versavel, Iftode, & Didier, 1977; McCoy, 1977; de Puytorac, Perez-Paniagua, & Perez-Silva, 1979b; Wirnsberger, Foissner, & Adam, 1985b). However, we have maintained the Order Cyrtolophosidida , which likely includes representatives similar to the common ancestor of the class. The order, character- ized by a simple paroral of dikinetids and several to many left oral polykinetids , includes ciliates with the basic features of the class and is comprised of the following families: Cyrtolophosididae , Platyophryidae , Woodruffiidae , and Sagittariidae . There is clearly a need for gene sequences from more representatives of this class to test the competing classifications (e.g., the one pro- posed here, Foissner, 1993a; de Puytorac et al., 1979b). Molecular studies would also resolve the placement of the Families Tectohymenidae and Pseudochlamydonellidae , which we consider incertae sedis in this class. 12.1 Taxonomic Structure 245 246 12. Subphylum 2. INTRAMACRONUCLEATA: Class 6. COLPODEA 12.2 Life History and Ecology Encystment is the life history feature that typifies the colpodeans . To our knowledge, all colpodeans can develop resistant resting cysts in response to desiccation. This has meant that more than any other class, their global distribution has been assured. Species of the genus Colpoda are notori- ous for this ability. Several studies have demon- strated the high vagility of Colpoda species by aerial dispersal (Maguire, 1963a, 1963b; Rivera et al., 1992). This high vagility is supported by studies that have not demonstrated any global biogeography in the genetic variation in ribosomal DNA within Colpoda species (Bowers & Pratt, 1995; Bowers, Kroll, & Pratt, 1998) nor in vari- ations in physiological responses, such as growth rate and sensitivity to toxicants (Xu, Bowers, & Pratt, 1997). Nevertheless, Foissner (1994b) noted some restrictions in biogeography of other genera: Orthokreyella and Tectohymena have only been reported from Laurasia while Puytoraciella , Apocolpoda , and Jaroschia have only been reported from Gondwanaland . Colpodeans are typically found in water associ- ated with mosses, forest litters, and soils where the water may range from fresh to brackish and salty. These so-called \u201cterrestrial\u201d ciliates have been found in these habitats in Europe and Asia (Detcheva, 1973; Foissner, 1980d, 1993a, 1994b; Griffiths, 2002; Grolière, 1977; Hattori & Hattori, 1993; Tirjaková & Matis, 1985; Vargas & Hattori, 1990), the Americas (Bamforth, 1973, 1980; Foissner, 1997c; Rivera et al., 1992), Africa (Buitkamp, 1977; Foissner, 1988c), Australia (Foissner, 1988c, 1990, 1997c), Antarctica (Ryan et al., 1989), and Hawaii (Foissner, 1993b, 1994c). Several unusual habitats include pitcher plants (Addicott, 1974; Rojo-Herguedas & Olmo, 1999) and tree holes (Novotny, Lynn, & Evans, 1977). Colpodeans have also been reported from streams, temporary ponds, and lakes in Europe (Foissner, 1979e, 1997b; Skogstad, Granskog, & Klaveness, 1987), the Americas (López-Ochoterena, 1966), and Africa (Dragesco, 1972; Njiné, 1979). However, relatively few species are truly limnetic, typically including species in the genera Bursaridium , Cyrtolophosis , and Pseudochlamydonella (Foissner, 1994b). Colpodeans are not typically marine although several species of Platyophrya and Woodruffia have been reported from marine environments (Kahl, 1930\u2013 1935)