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in lorica dimensions of tintinnids , correlated with the season (e.g., Gold & Morales, 1975) and water temperature (e.g., Boltovsky et al., 1995). Variation in community lorica oral diameter has been correlated with the average size of available prey, suggesting some kind of trophic specialization of tintinnids on their prey (Middlebrook, Emerson, Roff, & Lynn, 1987; Verity). However, Dolan (2000) concluded that trophic specialization , at least, is not the domi- nant factor determining tintinnid diversity in the Mediterranean Sea . Tintinnid diversity has been used to indicate different water masses in the North Pacific Ocean (Kato & Taniguchi, 1993). Spirotrichs are considered to be upstream filter feeders that \u201cselect\u201d particles primarily on the basis of the structural nature of the oral apparatus (Fenchel, 1980a, 1980b; Jonsson, 1986; Wilks & Sleigh, 1998). These theoretical predictions using various beads have been corroborated by feeding experiments on natural prey, which show a positive relation between size of the ciliate and the aver- age size of the prey that it can efficiently ingest (Bernard & Rassoulzadegan, 1990; Kamiyama & Arima, 2001). Benthic or substrate-oriented spirotrichs , like the hypotrich Euplotes and some substrate-oriented choreotrichs like Strobilidium , can likely survive on bacterivory in the wild (Lawrence & Snyder, 1998; Sime-Ngando, Demers, & Juniper, 1999). It is unlikely that pelagic oli- gotrichs and choreotrichs will achieve maximal growth rates by bacterivory since bacterial abun- dances are often less than the critical concentration of 10 6 ml -1 necessary to support growth (Bernard & Rassoulzadegan; Fenchel, 1980c; Macek, \u160imek, Pernthaler, Vyhnálek, & Psenner, 1996; \u160imek, Macek, Pernthaler, Stra\u161krabová, & Psenner, 1996). Nevertheless, behavioral modification of the swimming pattern may enable some oligo- trichs to exploit food patches of bacteria exceeding these minimum abundances (Fenchel & Jonsson, 1988) and enable some tintinnids to remain in patches of dinoflagellate prey (Buskey & Stoecker, 1989). Furthermore, chemosensory responses to prey particles may enable truly selective feed- ing by some tintinnids and oligotrichs (Burkill, Mantoura, Llewellyn, & Owens, 1987; Stoecker, 1988; Stoecker, Gallager, Langdon, & Davis, 1995; Taniguchi & Takeda, 1988; Verity, 1991). Selective food capture may also be enhanced by a lectin-type binding of prey to food-capturing cell membranes (Wilks & Sleigh, 2004). The puzzle of average bacterial abundances being too low to maintain the growth of planktonic spiro- trichs has had at least three solutions. First, these ciliates may be omnivorous in nature. Second, they may browse on particles where bacterial abundances are higher. Third, these ciliates may have behavioral mechanisms that maintain them in small-scale patches (Tiselius, Jonsson, & Verity, 1993; Montagnes, 1996). Patches of oligotrichs and choreotrichs ranged from <13 m to <77 m in size in a tropical coast lagoon under non-turbulent condi- tions (Bulit, Díaz-Avalos, Signoret, & Montagnes., 2003). Turbulence will destroy this patch structure , and it may also reduce the feeding efficiency of these ciliates, by changing either the rate or pattern of their locomotion (Dolan, Sall, Metcalfe, & Gasser, 2003). In recent years there has been considerable inter- est in the feeding biology of oligotrichs and chore- otrichs (Sanders & Wickham, 1993), particularly as they are dominant grazers in planktonic food webs. They can consume significant proportions of the primary production , up to 25% (Capriulo & Carpenter, 1983; Verity, 1985) and over 30% of the bacterial standing stock (Lavrentyev, McCarthy, Klarer, Jochem, & Gardner 2004; Rassoulzadegan, Laval-Peuto, & Sheldon, 1988; Sime-Ngando et al., 1999). Furthermore, their excretion of phos- phorus and ammonia may fuel over 15% of the net primary production (Dolan, 1997; Stoecker, 1984; Taylor, 1984; Verity). Field and laboratory studies have demonstrated that tintinnids con- sume cyanobacteria , picoflagellates , chlorophytes , prymnesiophytes , dinoflagellates , diatoms , euglen- ophytes , prasinophytes , and raphidophytes (Aelion & Chisholm, 1985; Bernard & Rassoulzadegan, 1993; Christaki, Jacquet, Dolan, Vaulot, & Rassoulzadegan, 1999; Dolan, 1991; Kamiyama & Arima, 2001; Rassoulzadegan & Etienne, 1981; Stoecker, 1984; Verity; Verity & Villareal, 1986). Toxic dinoflagellates , like Alexandrium , Gyrodinium , and Pfiesteria may increase tintinnid and oligotrich mortality, possibly due to secretion or ingestion of the toxins (Hansen, 1995; Hansen, Cembella, & Moestrup, 1992; Stoecker, Parrow, Burkholder, & Glasgow, 2002) as do thread-bear- ing diatoms (Verity & Villareal). However, the toxic effect is at least species-specific as some tintinnids and oligotrichs thrive on these toxic dinoflagellates (Kamiyama, Suzuki, & Okumura, 2006; Stoecker et al., 2002). Aloricate choreot- richs , such as Strobilidium , Lohmanniella and Strombidinopsis , consume bacteria , prymnesio- phytes , cryptophytes , dinoflagellates , chlorophytes , and prasinophytes (Burkill et al., 1987; Christaki, Dolan, Pelegri, & Rassoulzadegan, 1998; Jeong et al., 2004; Jonsson, 1986; Kamiyama & Matsuyama, 2005; Montagnes, 1996, 1999; Sime-Ngando et al., 1999). Diatoms , kinetoplastids , and eustigmato- phytes can be added to this list for aloricate oli- gotrichs , such as Strombidium species (Bernard & Rassoulzadegan, 1990; Burkill et al., 1987; Christaki et al., 1998, 1999; Fenchel & Jonsson, 1988; Jonsson; Montagnes, 1996; Ohman & Snyder, 1991). Tintinnids and oligotrichs generally consume food particles that are less than 20 µm in diameter (Rassoulzadegan, 1982; Rassoulzadegan et al., 1988). Stichotrichs , like Halteria , Oxytricha , and Stylony- chia , are probably omnivorous. They have been shown to feed on bacteria , diatoms , dinoflag- ellates , chrysophytes , cryptophytes , and chloro- phytes (Balczon & Pratt, 1996; Kaul & Sapra, 1983; Skogstad, Granskog, & Klaveness, 1987). Oxytricha and Onychodromus can feed on other ciliates, including members of their own spe- cies for which they may undergo a develop- mental polymorphism to become cannibal giants (Foissner, Schlegel, & Prescott, 1987; Riggio, Ricci, Banchetti, & Seyfert, 1987; Wicklow, 1988). Euplotes species are the only hypotrichs that have recently been examined for feeding preferences . They can be omnivorous, ingesting bodonids and a variety of heterotrophic flagellates , in addition to those prey mentioned for stichotrichs , and includ- ing other ciliates (Dolan & Coats, 1991a, 1991b; Gast & Horstmann, 1983; Lawrence & Snyder, 1998; Premke & Arndt, 2000; Wilks & Sleigh, 1998). Dini and Nyberg (1999) have convincingly demonstrated that ecologically important differ- ences in feeding responses among nine reproduc- tively isolated groups of Euplotes are genetically determined. They concluded that morphospecies inadequately represent the ecological diversity of ciliates. In addition to heterotrophy, some spirotrichs exhibit varying degrees of mixotrophy , either by sequestering chloroplasts from their prey or by harboring symbiotic Chlorella species (Sanders, 1991). Retention of prey chloroplasts is common in oligotrichs , with a significant fraction of the species exhibiting this trait in some oligotrophic lakes (Macek, Callieri, Simek, & Vazquez, 2006), in the Mediterranean (Bernard & Rassoulzadegan, 1994; Dolan & Pérez, 2000; Laval-Peuto & Rassoulzadegan, 1988), and in temperate oceans (Stoecker, Taniguchi, & Michaels, 1989). The chloroplasts appear to originate from a variety of groups of chromophytic protists, many of the groups noted above that can serve as