and soils of coastal dunes (Verhoeven, 2002). Finally, there have been a few reports of colpodeans as symbionts, probably commensals, within other organisms. A report by Powers (1933) of a Colpoda from the sea urchin intestines has never been con- firmed. Reynolds (1936) reported Colpoda as a facultative parasite of land slugs . Colpoda species have also been collected from the feces of deer (Bradbury & Outka, 1967) and amphibians and reptiles (Fernández-Galiano, Fernández-Galiano, & Madrigal-Sesma, 1986). Fernández-Galiano et al. (1986) concluded that this is likely due to ingestion by these animals of resting cysts attached to vegetation or in soil ; the colpodids probably do not excyst in the intestinal environment. The extreme body size range of colpodeans from 10 µm to over 500 µm is correlated with a similar breadth in the prey that can be consumed by different members of this class. Bacteria and picocyanobacteria , like Synechococcus , are the typical prey of the smaller species of Colpoda and Cyrtolophosis (Griffiths, 1986; Iriberri, Ayo, Santamaria, Barcina, & Egea, 1995; Šimek, Macek, Pernthaler, Straškrabová, & Psenner, 1996; Taylor & Berger, 1976). Colpoda may consume almost 1,000 bacteria per ciliate per hour (Hadas, Malinsky-Rushansky, Pinkas, & Cappenberg, 1998). Moderate-sized species can consume chlo- rophyte and cryptophyte algal cells (Skogstad et al., 1987; Wenzel & Winkler, 1984). Although some Colpoda species can ingest whole the cells of the yeast Saccharomyces (Wenzel & Winkler, 1984), the grossglockneriid colpodids apparently specialize on fungi with chitinous cells walls, which these ciliates penetrate with their tube-like cytopharynx (Petz, Foissner, & Adam, 1993). Finally, the larger colpodeans can ingest flagel- lates and other ciliates , including other colpodeans (Bradbury & Olive, 1980; Claff, Dewey, & Kidder, 1941; Foissner, 1990). Woodruffia metabolica appears to have a preference only for Paramecium species (Johnson & Larson, 1938; Salt, 1967). The growth rates of colpodeans can be predicted by the amount of macronuclear DNA, and are generally related to cell size : the larger the cell size , the more macronuclear DNA, and the slower the growth rate (Wickham & Lynn, 1990). The smaller species of bacterivorous colpodeans have been characterized as r -strategists with doubling times often less than 6 h (Drake & Tsuchiya, 1977; Lüftenegger, Foissner, & Adam, 1985). These col- podids commonly divide twice in a division cyst and may compose the majority of the species in extreme habitats (Foissner, 1994c). At the same time, they are not good competitors against more K -selected species , like Paramecium , which appar- ently can exclude Colpoda species from favorable habitats (Maguire, 1963a). The larger colpodeans, such as Bursaria and Woodruffia , have much longer doubling times, in the order of 12 h (Salt, 1967), and might be typified as K -selected forms . Colpodeans do not typically harbor symbionts. Endosymbiotic Chlorella have been described as mutuals in Paracondylostoma , Platyophrya , and Thylakidium species (Foissner, 1993a; Foissner & Kreutz, 1998; Kawakami, 1991). Parasites of colpo- deans include the flagellate Spiromonas (Foissner & Foissner, 1984), Ciliatosporidium , a presumed micro- sporidian (Foissner & Foissner, 1995), and the pro- teomyxid -like Endemosarca (Erdos & Olive, 1971). Suctorians can also be parasites/predators of larger colpodeans , like Bursaria (Jankowski, 1973d) while insect larvae and cladocerans are among the metazoan predators of these ciliates (Addicott, 1974; Cochran- Stafira & von Ende, 1998; Jack & Gilbert, 1993). A discussion of the life history of the Class COLPODEA must include some aspects of the resting or resistant cysts of these ciliates. The literature on this aspect of their biology, crypto- biosis , is significant and has been reviewed most recently by Gutiérrez, Izguierdo, Martín-González, & Callejas, (1998b). Colpoda species have sur- vived from 5 years (Dawson & Hewitt, 1931) to 38 years (Goodey, 1915) in laboratory settings so it is likely that their survivability under natural conditions might be even more extensive. As with other ciliates, encystment may also be stimulated by reduced abundances of prey (Barker & Taylor, 1931; Johnson & Evans, 1941; Salt, 1967) and also increasing concentrations of ions, such as Ca+2 , Na + , and K + , possible signals for impend- ing desiccation (Yamaoka, Watoh, & Matsuoka, 2004). Excystment is stimulated by the presence of prey and excystment rate and “efficiency” can be dependent, for example, upon the quality of the food preceding encystment (Wenzel & Meier- Tackmann, 1975). Earlier physiological research (e.g., Barker & Taylor, 1931; Beers, 1945, 1948; Johnson & Evans, 1939; Taylor & Strickland, 1939) was followed by research on the “cell biol- ogy” of encystment in the early days of electron microscopy. Kawakami and Yagiu (1964) com- pleted their sixth paper on the changes in the fine structure of Colpoda cucullus during its life cycle, having described the formation of the cyst wall and the excystment of the ciliate. The cyst wall is composed of two layers, an outer ectocyst and an inner endocyst, probably created by exocystosis of the cortical mucocysts (Martín-González, Benitez, Palacios, & Gutiérrez, 1992b; Ruthmann & Kuck, 1985; Tibbs, 1968). Freeze-etching suggests a third outer mucous layer in Colpoda (Janisch, 1980). The resting cyst of Bursaria has a conspicuous emergence pore (Foissner, 1993a) and may have a fibrous middle or mesocyst layer connecting the ectocyst and endocyst (Sergejeva et al., 1995). The cyst wall components of Colpoda species are rich in glutamic acid while its glycoproteins have high mannose content (Izquierdo, Martín-González, Diaz, & Gutiérrez, 1999; Tibbs & Marshall, 1970). The profiles and distributions of glycoproteins may change in the cyst wall as the cysts age (Chessa et al., 2002). Since ciliature and infraciliature are partially, but not completely, resorbed during encystment , colpodean cysts are typed as par- tial kinetosome-resorbing cysts (Martín-González, Benitez, & Gutiérrez, 1992a). Gutiérrez, Izguierdo, Martín-González, & Callejas, (1998b) have argued that colpodid cystment serves as an interesting model for exploration of the cell and molecular biology of cryptobiosis , a life history feature common to both prokaryotes and eukaryo- tes. Encystment requires RNA and protein synthesis (Ruthmann & Kuck, 1985). In the cryptobiotic state, there is protein turnover and evidence for encystment - specific mRNA (Benitez & Gutiérrez, 1997; Gutiérrez & Martín-González, 1990). In addition to cytoplasmic changes, the macronucleus in particular undergoes sub- stantial changes during this process (Gutiérrez, Martín- González, & Callejas, 1998a). The macronuclear chromatin condenses into large bodies several times the size of those in interphase cells (Frenkel, 1992; Popenko, Cherny, Ivanova, & Yakovleva, 1998a). This process is accompanied by extrusion of macronuclear fragments, a process that appears to regulate the DNA amount in proportion to cell size (Morat, Chessa, & Crippa-Francheschi, 1981). Extrusion of condensed chromatin may also occur at excystment (Chessa, Gallus, Tiano, Trielli, & Corrado, 2001). 12.2 Life History and Ecology 247 248 12. Subphylum 2. INTRAMACRONUCLEATA: Class 6. COLPODEA It would be remiss not to add to the discussion of cryptobiosis in colpodeans a description of the structure and development of the aerial sorocarps produced on a stalk by Sorogena stoianovitchae , which was originally found in tropical habitats (Olive, 1978), but has now been found in the canopy of European deciduous