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Rhabdostyla , Vorticella , and Trichodina (Figs. 4.3, 4.6, Table 4.1), are a speciose assemblage that is not strongly supported by molecular phylogenies. The somatic kinetids are generally similar to those of the previous two classes. However, the somatic kinetids of the subclass Peniculia are more similar to those of other groups, like the hypotrichs , and the somatic kinetids of the trochal girdle of the subclass Peritrichia are highly divergent (Fig. 4.7; see Chapter 15 ). It is really only the paroral and the three adoral polykinetids that all these genera share, affirming the 20th century view that oral features are indeed indicative of common ancestry! Fig. 4.5. Scanning electron micrographs of ciliate diversity. A\u2013B Class ARMOPHOREA . Metopus ( A ) and Nyctotherus ( B). C\u2013G Class LITOSTOMATEA . The haptorians Didinium ( C ) and Dileptus ( D ) and the trichostomes Isotricha ( E ), Entodinium ( F ), and Ophryoscolex ( G ). H Class COLPODEA . Colpoda . I Class PROSTOMATEA . Coleps . (Micrographs courtesy of E. B. Small.) 4.2 Life History and Ecology The life history of a typical ciliate would include an asexual or vegetative cycle during which growth and cell division occur, a sexual cycle during which the exchange of genetic material occurs between conjugants , and a cryptobiotic cycle during which the organism would typically form a resting cyst (Fig. 4.8). These life histories, however, are diverse and undoubtedly adaptive. The cyst forms are diverse, stimulated by a variety of conditions to both encyst and excyst (Bussers, 1984; Corliss & Esser, 1974), and a complex set of physiological changes, for example, \u201cswitched on\u201d by gene expression, accompany the development of the cryptobiotic state (Gutiérrez, Martín-González, & Matsusaka, 1990). One adaptive variation involves the presence or absence of the cryptobiotic cycle Fig. 4.6. Scanning electron micrographs of ciliate diversity. A , B , D , E , G\u2013I Class OLIGOHYMENOPHOREA . The peritrichs Rhabdostyla ( A ), Vorticella with its helically contracted stalk ( B ), and Trichodina with its suction disk ( D , E). The peniculines Paramecium ( G , ventral on left and dorsal on right) and Lembadion ( H ). The hymenos- tome Glaucoma ( I ). C , F Class PHYLLOPHARYNGEA . The cyrtophorian Trithigmostoma ( C ) and the suctorian Podophrya ( F ). (Micrographs courtesy of E. B. Small, A. H. Hofmann, and C. F. Bardele.) 4.2 Life History and Ecology 99 100 4. Phylum CILIOPHORA \u2013 Conjugating, Ciliated Protists with Nuclear Dualism and, related to this, differences in the survivability of the non-encysted stages (Jackson & Berger, 1985a, 1985b). Often, the starving trophont trans- forms into a highly motile form, the theront, which may be adapted both for dispersal and very long survival (Fig. 4.8) (Fenchel, 1990; Nelsen & DeBault, 1978). A common adaptive variation is the differentiation of macrostome cannibal forms \u2013 ciliates that differ- entiate a new oral apparatus large enough to ingest their microstomatous siblings (de Puytorac, 1984b) (Fig. 4.8). This transformation is often induced by starvation, like the theront transformation mentioned above. More dramatic examples of adaptation are found in symbiotic forms, especially parasitic ones (Bradbury, 1996). Ichthyophthirius , the parasite of fish gills and epithelium, apparently lacks a typical resting cyst stage. Instead, it grows to a consider- able size as a trophont on the fish host, then drops off the host and becomes a tomont in a reproductive cyst. The tomont divides to produce thousands of tomites , which may reside for some time within the cyst before breaking out to find the next host. Finally, hyperparasites or hyperpredators can be Fig. 4.7. Schematics of somatic kinetids of genera representative of each class in the Phylum Ciliophora. ( a ) Loxodes \u2013 Class KARYORELICTEA ; ( b ) Blepharisma \u2013 Class HETEROTRICHEA ; ( c , d ) Protocruzia ( c ), Euplotes ( d ) \u2013 Class SPIROTRICHEA ; ( e ) Metopus \u2013 Class ARMOPHOREA ; ( f ) Balantidium \u2013 Class LITOSTOMATEA ; ( g) Chilodonella \u2013 Class PHYLLOPHARYNGEA ; ( h ) Obertrumia \u2013 Class NASSOPHOREA ; ( i) Colpoda \u2013 Class COLPODEA ; ( j ) Plagiopyla \u2013 Class PLAGIOPYLEA ; ( k ) Holophrya \u2013 Class PROSTOMATEA ; ( l) Tetrahymena \u2013 Class OLIGOHYMENOPHOREA ; ( m ) Plagiotoma \u2013 Class SPIROTRICHEA . Kd \u2013 kinetodesmal fibril; Pc \u2013 post- ciliary microtubular ribbon; T \u2013 transverse microtubular ribbon (from Lynn, 1981, 1991) found among the apostome oligohymenophoreans : Phtorophrya insidiosa is an apostome that attacks other apostomes, which are themselves symbionts on the cuticle of crustaceans (see Fig. 3.1). Ciliates are heterotrophic, exhibiting a wide range of feeding behaviours, and occupying a diversity of ecological niches (Dragesco, 1984b; Finlay & Fenchel, 1996). As noted above, some can transform to feed on their siblings, which in the vast majority of cases are suspension feeders (Fenchel, 1980a, 1980b). The \u201cparticles\u201d removed from suspension can be very small, like viruses and bacteria , moderately-sized, like various kinds of unicellular algae, and relatively large, like other ciliates. The varieties of specific prey chosen by ciliates in the different classes are detailed in Fig. 4.8. Life cycle stages of ciliates. A microstome trophont , typically feeding on bacteria, grows from the tomite stage until it roughly doubles in size to become a dividing tomont . This vegetative or asexual cycle can repeat itself as long as food is present. If food becomes limiting the ciliate may transform to a macrostome trophont , which is a cannibal form that can eat tomites and smaller microstome trophonts or other ciliates. If food is limiting or other stressful environmental circumstances prevail, the ciliate may form a cyst or may transform into a theront , a rapidly swimming dispersal stage. If the theront does not find food, it too may encyst . In unusual circumstances, when food is depleted and a complementary mating type is present, the ciliates may fuse together as conjugants and undergo the sexual process of conjugation 4.2 Life History and Ecology 101 102 4. Phylum CILIOPHORA \u2013 Conjugating, Ciliated Protists with Nuclear Dualism the following chapters. Bacterivorous ciliates are particularly important in maintaining the \u201cquality\u201d of effluent from sewage treatment plants as they can reduce bacterial densities ten-fold by their feeding (Curds & Cockburn, 1970a, 1970b; Foissner, 1988a; Madoni, 2003) and may even consume viruses (Pinheiro et al., 2007). In addition to being symbionts in other organisms (Bradbury, 1996; Fernández-Leborans & Tato- Porto, 2000a, 2000c; Levine, 1972; Song, 2003), a variety of other organisms can use ciliates as their host (Ball, 1969). These endosymbionts of ciliates can range from bacteria living in the micronucleus (Görtz, 1983, 1996; Hovasse, 1984b) to various spe- cies of algae (Hovasse, 1984a; Lobban et al., 2002; Reisser, 1986). Ciliates are distributed globally in a diversity of habitats where they function as important trophic links in a variety of food webs (Adl, 2003; Finlay & Fenchel, 1996; Foissner, 1987; Pierce & Turner, 1992; Sanders & Wickham, 1993). They are found in the world\u2019s oceans, in the plankton (Edwards & Burkhill, 1995; Lynn & Montagnes, 1991; Pierce & Turner, 1993; Strom, Postel, & Booth, 1993), on ocean shores (Agamaliev, 1971; Al-Rasheid, 1999d; Dragesco, 1965; Kovaleva & Golemansky, 1979), in ocean depths (Fenchel et al., 1995; Hausmann, Hülsmann, Polianski, Schade, & Weitere, 2002; Silver, Gowing, Brownlee, & Corliss, 1984), and associated with sea ice (Lee & Fenchel, 1972; Song & Wilbert, 2000b). They are found in a variety of \u201cland-locked\u201d waters, including freshwater bodies, such