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et al., 2001; Snoeyenbos-West et al., 2002; Strüder-Kypke et al., 2002). The possession of macronuclear repli- cation bands unites the latter five subclasses while a dorsoventral differentiation unites phacodiniids with hypotrichs and stichotrichs. Since it is likely that halteriids have evolved a planktonic life style from benthic stichotrich ancestors like Oxytricha , it is very likely that oligotrichs and choreotrichs are also derived from benthic dorsoventrally- differentiated ancestors. Perhaps future phylo- genetic analyses based on genes other than the SSUrRNA gene will shed light on these unresolved phylogenetic relationships. Applications of molecular methods have enabled the identification of a number of spirotrichs spe- cies. Ammermann, Schlegel, and Hellmer (1989) distinguished the sibling species Stylonychia mytilus and Stylonychia lemnae using isozymes of isocitrate dehydrogenase . Haentzsch et al. (2006) have now used a PCR method based on this gene to clearly identify these sibling species , while Schmidt, Bernhard, Schlegel, and Fried (2006b) have used fluorescence in situ hybridization ( FISH ) of SSUrDNA probes for the same purpose. Others have employed either random amplified polymor- phic DNA ( RAPD ) fingerprinting or restriction fragment length polymorphisms ( RFLPs ) to distin- guish species and populations of hypotrichs , such as Euplotes (Chen, Song, & Warren, 2001; Kusch & Heckmann, 1996; Shang, Chen, & Song, 2002) and Uronychia (Chen, Song, & Warren, 2003). Finally, monographic works have recently appeared on the spirotrichs . These include monographs on the hypotrichs and stichotrichs by Berger (1999, 2001, 2006a, 2006b) and tintinnids (Alder, 1999). 7.2 Life History and Ecology As noted above, spirotrichs are broadly distributed, both as symbionts and free-living forms. There is not a large number of symbiotic spirotrichs , but what species there are colonize a diverse array of hosts. For example, Licnophora is found in holothurian echinoderms (Stevens, 1901), on the eyes of scallops (Harry, 1980), on cyanobacterial filaments (Fauré-Fremiet, 1937), and in the man- tle cavity of limpets (Van As, Van As, & Basson, 1999); Kerona polyporum is found on the body of Hydra (Hemberger & Wilbert, 1982); Trachelostyla tani is found in the mantle cavity of the scallop Chlamys (Hu & Song, 2002); Strombidium is found associated with echinoid echinoderms (Jankowski, 1974b; Xu, Song, Sun, & Chen, 2006); Euplotes tuffraui is also associated with echinoid echi- noderms (Berger, 1965); Euplotaspis associates with the chambers of ascidian tunicates (Chatton & Séguéla, 1936); and Plagiotoma is an obligate endosymbiont in the digestive tract of oligochaete annelids (Albaret, 1973; Mandal & Nair, 1975). Free-living hypotrichs and stichotrichs occupy a wide range of habitats from freshwater to brackish to marine, in sands and soils , and edaphic habitats. They are typically substrate-oriented and benthic, and are particularly prominent in soil ecosystems from Europe to Antarctica (Berger & Foissner, 1987, 1989a; Blatterer & Foissner, 1988; Foissner, 1980a, 1982; Petz & Foissner, 1997) where they may represent over 30% of the species richness and may attain abundances of up to 1,000 g -1 of dry soil. Hypotrichs and stichotrichs have also been recorded in aquatic habitats from arctic and antarctic ice (Agatha, Spindler, & Wilbert, 1993; Agatha, Wilbert, Spindler, & Elbrächter, 1990; Garrison et al., 2005), in benthic communities in the deep Mediterranean Sea (Hausmann, Hülsmann, Polianski, Schade, & Weitere, 2002), in freshwater ponds in Great Britain (Finlay & Maberly, 2000), in streams and rivers in Europe (Cleven, 2004; Foissner, 1997b), in tropical littoral habitats (Al- Rasheid, 1999a; Dragesco & Dragesco-Kernéïs, 1986), and associated with leaf litter in mangrove forests in India (Dorothy, Satyanarayana, Kalavati, Raman, & Dehairs, 2003). Isolates from different regions have demonstrated adaptations to those environments: Antarctic Euplotes species show growth rate optima at lower temperatures than tem- perate and tropical isolates (Lee & Fenchel, 1972) as do temperate isolates of the halteriid Meseres compared to tropical and subtropical isolates (Gachter & Weisse, 2006). These cold adapta- tions arise in some Euplotes species through gene mutations in protein-coding genes that increase the molecular flexibility of these proteins at low temperatures (Pucciarelli, Marziale, Di Giuseppe, Barchetta, & Miceli, 2005). Oligotrichs and choreotrichs have been exten- sively studied in recent years in both freshwa- ter (e.g., Beaver & Crisman, 1989a; Foissner, Berger, & Schaumburg, 1999; Obolkina, 2006; Sonntag, Posch, Klammer, Teubner, & Psenner, 2006; Zingel, Huitu, Makela, & Arvola, 2002) and brackish water lakes (Pfister, Auer, & Arndt, 2002) and marine (e.g., Lynn & Montagnes, 1991; Pierce & Turner, 1992; Sanders & Wickham, 1993) eco- systems, where they can be found in both neritic and eupelagic regions. For marine species, the vast majority of studies are not unexpectedly local- ized near sites of marine laboratories (see Lynn & Montagnes, 1991). Tintinnid choreotrichs have been quite extensively sampled over all the world\u2019s oceans, ranging from the arctic to the antarctic (Pierce & Turner, 1993). Some taxa show unusual biogeographic distributions , but these must be interpreted with some caution since tintinnids can survive in ballast water and be distributed globally by humans (Pierce, Carlton, Carlton, & Geller, 1997). Marine oligotrichs are equally broadly dis- tributed with recent reports from northern (Dale & Dahl, 1987a; Stelfox-Widdicombe, Archer, Burkill, & Stefels, 2004) and southern oceans (Pettigrosso, Barria de Cao, & Popovich, 1997) to the trop- ics (Al-Rasheid, 1999; Lynn, Roff, & Hopcroft, 1991a) and Antarctica (Garrison et al., 2005; Leakey, Fenton, & Clarke, 1994; Petz, 1994). Oligotrichs and choreotrichs are now considered to play an important role inmicrobial food webs (e.g., Beaver & Crisman, 1989b; Pierce & Turner, 1993; Sanders & Wickham, 1993; Weisse, 2006). Aloricate oligotrichs (e.g., Strombidium , Tontonia , Laboea ) and choreotrichs (e.g., Strobilidium , Strom bidinopsis ) tend to dominate the abundance, ranging from tens to thousands per liter. Mean annual abundances are typically 1,000 l -1 (Lynn, Roff, & Hopcroft, 1991a; Montagnes, Lynn, Roff, & Taylor, 1988; Moritz, Montagnes, Carleton, Wilson, & McKinnon, 2006), but exceptionally high abundances of over 106 l -1 have been recorded (e.g., Dale & Dahl, 1987a). Tintinnid choreotrichs typically comprise a smaller fraction of the total ciliate abundance, ranging up to 25% of the abundance of their aloricate relatives (e.g., Abboud-Abi Saab, 1989; Gilron, Lynn, & Roff, 1991; Lynn et al., 1991a). Because of their loricae, which are easily preserved, there is an extensive literature on the ecology of tintinnids . Tintinnid abundances average in the 10s l -1 in places as geographically distant as the Mediterranean (Abboud-Abi Saab; Cariou, Dolan, & Dallot, 1999; Krsinic & Grbec, 2006), Greenland Sea (Boltovsky, Vivequin, & Swanberg, 1995), Barents Sea (Boltovsky, Vivequin, & Swanberg, 1991), and off the cost of Japan (Dohi, 1982). 7.2 Life History and Ecology 151 152 7. Subphylum 2. INTRAMACRONUCLEATA: Class 1. SPIROTRICHEA However, abundances of 500 l -1 (Cariou et al., 1999) may occur seasonally, with particularly high abun- dances, to over 10,000 l -1 , being associated with estuarine and near shore locations, for exam- ples, in North America (Capriulo & Carpenter, 1983; Verity, 1987), South America (Barría de Cao, 1992), and China (Zhang & Wang, 2000). Variations have been reported