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food for these ciliates (Laval-Peuto & Febvre, 1986; Stoecker, Silver, Michaels, & Davis, 1988/1989). These chloroplasts remain functional for several days in Laboea and Strombidium , enabling the ciliate to fix carbon during this time (Perriss, Laybourn- Parry, & Jones, 1994; Stoecker, Michaels, & Davis, 1987a; Stoecker, Silver, Michaels, & Davis, 1988). Mixotrophy may serve a variety functions for the ciliate, including providing fixed carbon during periods when prey are not abundant (Dolan & Pérez, 2000; Stoecker et al., 1987a) and oxygen in those species that prefer to live at the oxic-anoxic boundary in freshwater ponds (Berninger, Finlay, & Canter, 1986). As abundant components of aquatic ecosystems, spirotrichs can also be consumed by other organ- isms, serving as links to higher trophic levels (Sanders & Wickham, 1993). Choreotrichs and tintinnids are consumed by rotifers (Gilbert & Jack, 1993), copepods (Burns & Gilbert, 1993; Gismervik, 2006; Pérez, Dolan, & Fukai, 1997; Stoecker & Sanders, 1985; Turner, Levinsen, Nielsen, & Hansen, 2001; Wiackowski, Brett, & Goldman, 1994; Wickham, 1995), cladocer- ans (Jack & Gilbert, 1993; Wickham & Gilbert, 1991; Wickham, Gilbert, & Berninger, 1993), barnacle nauplii (Turner et al., 2001), euphausiids (Nakagawa, Ota, Endo, Taki, & Sugisaki, 2004), scyphozoan jellyfish (Stoecker, Michaels, & Davis, 1987b), larval and post-larval ctenophores (Stoecker, Verity, Michaels, & Davis, 1987c), nematode worms 7.2 Life History and Ecology 153 154 7. Subphylum 2. INTRAMACRONUCLEATA: Class 1. SPIROTRICHEA (Hamels, Moens, Muylaert, & Vyverman, 2001), freshwater oligochaetes (Archbold & Berger, 1985), oysters (Loret et al., 2000), and larval fish (Nagano, Iwatsuki, Kamiyama, & Nakata, 2000; Olivotto et al., 2005; Stoecker & Govoni, 1984). They are even consumed by other protists, both ciliates and dinoflagellates (Bockstahler & Coats, 1993; Dolan, 1991; Smalley & Coats, 2002; Smalley, Coats, & Adam, 1999). Planktonic ciliates, in their turn, have inde- pendently evolved jumping movements to escape predation (Tamar, 1979). In the case of the suspen- sion feeding crustaceans, the choreotrichs , like Strobilidium , and the stichotrich Halteria have independently evolved a jumping behavior that significantly reduces encounters with predators (Gilbert, 1994), even relative to loricate tintinnids (Broglio, Johansson, & Jonsson, 2001). The ciliates are apparently responding to a hydromechanical signal, very likely deformations of fluid flows caused by the suction-feeding currents of the pred- ators (Jakobsen, 2000, 2001). Euplotes undergoes an \u201c escape response \u201d in the presence of the turbel- larian predator Stenostomum (Kuhlmann, 1994). For \u201csofter\u201d-bodied predators, like other ciliates, oligochaetes , and turbellarians , Euplotes species develop an enlarged circular, \u2018winged\u2019 form that is much less easily consumed (Fyda, Warren, & Wolinska, 2005; Kuhlmann & Heckmann, 1985, 1994; Kusch, 1995). This \u2018winged\u2019 form develops under the influence of a diffusible protein morphogen or kairomone when the ciliate predator is Lembadion (Kuhlmann & Heckmann; Peters-Regehr, Kusch, & Heckmann, 1997). The kairomone induces the assembly of new microtubular structures to support the \u2018wings\u2019 (Jerka-Dziadosz, Dosche, Kuhlmann, & Heckmann, 1987). Onychodromus quadricornutus develops large dorsal spines in response to the predator Lembadion (Wicklow, 1988), although the ultrastructural basis of this development has not yet been determined. These morphological defenses are genetically variable among clones, suggesting that natural selection can act on them to favor the more fit variants (Duquette, Altwegg, & Anholt, 2005; Wiackowski, Fyda, Pajdak-Stós, & Adamus, 2003). Marine Euplotes species also secrete a variety of terpenoids , which are strain and species specific. These have been shown to have biological activity, killing both conspecifics that could be potential competitors (Dini, Guella, Giubbilini, Mancini, & Pietra, 1993) and predators, such as the haptorian Litonotus (Guella, Dini, & Pietra, 1995; Guella, Dini, & Pietra, 1996). The most bizarre predator defense , probably among all the ciliates, is that exhibited by the hypotrich Euplotidium : it carries bacterial ectosymbionts that explode on contact with the predatory ciliate Litonotus , defending their host against predation (Verni & Rosati, 1990; Petroni, Spring, Schleifer, Verni, & Rosati, 2000)! Symbionts of spirotrichs can be categorized as both beneficial (i.e., mutualistic ) and harmful (i.e., parasitic ). Bacteria , as in Euplotidium above, have been observed on the outside of tintinnid loricae, and also as intracellular forms (Laval-Peuto, 1994). Their role in tintinnids is not known. However, both freshwater and marine species of the hypot- rich Euplotes depend upon bacterial symbionts for cell growth. Aposymbiotic Euplotes fail to divide and ultimately die (Heckmann, 1975, 1983; Heckmann & Schmidt, 1987; Heckmann, Ten Hagen, & Görtz, 1983; Vannini, Schena, Verni, & Rosati, 2004). However, Fujishima and Heckmann (1984) rescued aposymbiotic freshwater Euplotes by transfer of bacterial symbionts even among species of Euplotes , suggesting that the common ancestor of this group of Euplotes species inher- ited a hereditary defect in cell division that was rescued by its bacterial endosymbiont . At the other extreme, some bacterial endosymbionts carried by Euplotes species kill sensitive cells of the same species, either by liberating toxins into the medium or by transfer of toxins and bacteria during mat- ing, a phenomenon also reported in Paramecium species (Verni, Rosati, & Nobili, 1977; see review by Heckmann, 1983). Fenchel and Bernard (1993) have described an unusual association between the obligately anaerobic Strombidium purpureum and its photosynthetic purple non-sulphur bacteria , an analogy to the symbiosis that is believed to have lead to the evolution of mitochondria. Eukaryotic symbionts of spirotrichs have also been observed. Chlorella species are often found in hypotrichs and stichotrichs , whose photobe- havior may be influenced by the presence of the symbiont (Reisser, 1984; Reisser & Häder, 1984). These Chlorella species are typical photo- synthetic symbionts that presumably at least provide organic sugars to their hosts. Other protists are not as friendly. Species of the kineto- plastid Leptomonas infect the macronucleus of the stichotrich Paraholosticha sterkii and the hypot- rich Euplotes , causing death in some strains of these species (Görtz & Dieckmann, 1987; Wille, Weidner, & Steffens, 1981). One of the most unu- sual flagellate infections of spirotrichs is that of the parasitic dinoflagellate Duboscquella (Coats, 1988; Coats, Bockstahler, Berg, & Sniezek, 1994). Species of Duboscquella that kill the tintinnid host may even regulate host abundances in natural populations (Coats & Heisler, 1989). Foissner and Foissner (1986) have described a zoosporic fun- gus , Ciliomyces spectabilis , that invades and kills the cysts of the stichotrich Kahliella simplex . Spirotrichs have complex behaviors that have been extensively investigated. Ricci and his research group have introduced the ethogram as a quantita- tive approach to characterizing behavior, especially of hypotrichs and stichotrichs (e.g., Banchetti, Erra, Ricci, & Dini, 2003; Leonildi, Erra, Banchetti, & Ricci, 1998; Ricci, 1990; Ricci, Cionini, Banchetti, & Erra, 1999). In addition to thigmotactic responses by benthic forms to the texture of substrate surfaces (Ricci, 1989) and water current (Ricci et al., 1999), planktonic forms demonstrate a negative geotaxis that is influenced by temperature and light and that explains their vertical