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1979a, 1979b). Mucocyst abundance varies through- out the life cycle with depletions in their abundance correlated with encystment (Delmonte Corrado et al., 1996; Suhama, 1969). Mitochondria are the typical tubular forms characteristic of ciliates. They may be distributed throughout the cortex or anchored in the cortex, possibly by filamentous elements associated with the microtubular ribbons of the somatic kinetids (Lynn, 1977a). The cytoproct , when it has been described, is usu- ally located near the contractile vacuole (Foissner, 1993a). 12.4 Oral Structures Colpodeans have a permanent cytostome and an oral cavity that is typically in the anterior third of the cell (Figs. 12.1, 12.2). Marynids with their posterior oral cavity are an exception to this general description (Foissner, 1993a). The size of the oral apparatus essentially varies with body size: the larger ciliates, such as Bursaria , typically have a larger oral cavity (Fig. 12.1). However, this is not always the case. Some carnivorous colpodids, like Bresslaua , are smaller than some of the larger bacterivorous species of Colpoda (e.g., Colpoda magna ) (Foissner, 1993a). As noted in Chapter 1 , the colpodeans superficially have extremely vari- able oral structures (Fig. 1.4) (Foissner, 1993a). However, upon closer examination and especially through detailed analyses of stomatogenesis (see below Division and Morphogenesis ), there is an underlying unity to the diversity of patterns. Fig. 12.4. Somatic cortex of a typical colpodean interpreted based on the somatic cortex of several colpodeans , such as Colpoda and Bursaria The cyrtolophosidids , bursariomorphids , and bry- ophryids have several to many adoral polykinetids oriented along the left side of the oral cavity (Figs. 12.1, 12.2). These can be composed of a basic two rows of kinetosomes, constructed by the side to side assembly of dikinetids, joined by dense connec- tives in a square-packed or hexagonal arrangement. A third row can often appear during stomatogenesis (Bardele et al., 1991; Didier et al., 1980; Golder & Lynn, 1980). Colpodids have a large left oral polykinetid composed of regularly spaced rows, which may be linked by connectives both within and between rows (Garcia-Rodriguez, Perez-Paniagua, & Perez-Silva, 1981; Hofmann-Münz, 1991; Lynn, 1976a, 1976b, 1976c, 1977; Perez-Paniagua et al., 1979a, 1979b). The single, small adoral polyki- netid of grossglockneriid colpodids also probably has an organized kinetosomal arrangement (Aescht et al., 1991; de Puytorac, Didier, Detcheva, & Foissner, 1983a). Postciliary ribbons extend from these kinetosomes to support the cytopharnynx. The right oral kinetids in the cyrtolophosidids , bursariomorphids , and bryophryids are minimally organized as a paroral composed of dikinetids. Both kinetosomes are ciliated while the postciliary ribbon from the left kinetosome extends to support the cytopharynx (Bardele et al., 1991; Didier et al., 1980; Golder & Lynn, 1980). Hofmann-Münz (1991) was the first to dem- onstrate that there was some order to the right oral field of colpodids , which had been described previously as unordered (Garcia-Rodriguez et al., 1981; Lynn, 1976c, 1977a; Perez-Paniagua et al., 1979a; but see also Perez-Paniagua & Perez-Silva, 1978). A dikinetid file may extend along the right border of the right oral polykinetid. This \u201cparoral\u201d is composed of a single file of kinetosomes whose orientation is similar to the left kinetosome of the paroral kinetids of the other orders, while the right kinetosome of the paroral dikinetids in colpodids is oriented at 180° as judged by the orientation of the postciliary microtubules. An unordered field of kinetosomes is arrayed to the right of this \u201cparoral\u201d (Hofmann-Münz, 1991). In the grossglockneriid colpodids , whose oral ciliature is quite reduced, the right oral ciliature is just a single file of kinetosomes bearing a postciliary ribbon that extends anteriorly to support the sucker (Aescht et al., 1991; de Puytorac et al., 1983a). As noted before, the grossglockneriids have a small feeding tube , supported by lamellae of microtubules reminiscent of the arrangement of the phyllae in the cytopharynx of the phyllopharyngeans and presumed to be derived during stomatogen- esis from postciliary microtubular ribbons (Aescht et al.; de Puytorac et al., 1983a). Except for the unusual mycophagous gross- glockneriids (Petz, Foissner, & Adam, 1993), colpodeans can be characterized as suspension or filter feeders . Fenchel (1980a) has described Bursaria as an upstream filter feeder , using the spacing between its left oral polykinetids to trap prey ciliates larger than 8\u201310 µm, which is the average spacing between these structures. Fenchel (1980a) was unable to determine which oral struc- ture of colpodids was responsible for retaining the particles since the species that he described fed while swimming. The smaller Colpoda steinii cleared larger particles, about 1 µm diameter, more efficiently than the larger Colpoda cucullus , which optimally cleared particles slightly less than 0.4 µm (Fenchel, 1980b). Since the left oral field of colpo- dids is ordered, one is tempted to speculate that this provides the filter in these species. As in other ciliates, colpodeans form food vacuoles in which prey digestion occurs (Rudzinska, Jackson, & Tuffrau, 1966). 12.5 Division and Morphogenesis Colpodeans divide either free-swimming or within a cyst . Parental oral structures may be partially or completely reorganized. The colpodids are the group classically considered to divide in reproductive cysts . However, under exceptional circumstances even colpodids may divide while swimming freely (Stuart, Kidder, & Griffin, 1939). Division within a cyst is typically palintomic , that is typically two divisions occur with no DNA S-phase occurring between them (Foissner, 1993a). Tuffrau (1952) provided details of silver-stained dividing colpodids and demonstrated that all the parental oral structures dedifferentiated and the ciliates were essentially astomatous during palintomy . Following cytokinesis , kinetosomal proliferation occurred at the ends of some of these somatic kineties to provide kinetosomes for the new oral structures (Fig. 12.5). Hashimoto (1966) confirmed both that the same kind of stomatogenesis occurred in colpodids excysting from resting cysts and that the number of somatic 12.5 Division and Morphogenesis 253 254 12. Subphylum 2. INTRAMACRONUCLEATA: Class 6. COLPODEA kineties involved increased as the size of the species increased. Foissner (1996b) has typed this as merotelokinetal stomatogenesis since the ends of only a limited number of somatic kineties are involved. Since Tuffrau (1952) and Hashimoto (1966), several studies have demonstrated that the left oral polykinetid is derived by the fusion of \u201csubpolykinetids\u201d composed of three rows of kinetosomes, which are initially derived from diki- netids. The right oral polykinetid is assembled by a file of dikinetids along the border of the primordial field and to its right there is a field of unordered kinetosomes derived by kinetosomal replication of somatic kinetosomes (Garcia-Rodriguez et al., 1981; Perez-Paniagua & Perez-Silva, 1978; Perez- Paniagua et al., 1979a, 1979b). The pattern in colpodids is undoubtedly derived from the pattern demonstrated by representatives of the other colpodean orders, at least if we use the molecular phylogenies as the basis for polarizing stomatogenetic patterns in this class. Foissner (1996b) characterizes the alternate pattern as pleu- rotelokinetal since oral kinetosomal proliferation occurs within, and sometimes between, several kineties on the right side of the body and on both sides of the fission zone.