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They can have significant grazing impacts 
on bacterial and picocyanobacterial communities, 
ingesting over 4,000 bacteria per cell per hour and 
sometimes over 500 picocyanobacteria per cell 
per hour (Callieri, Karjalainen, & Passoni, 2002; 
Šimek, Bobková, Macek, Nedoma, & Psenner, 
1995). This demonstrates their importance as 
components of the community in sewage treat-
ment facilities . Their influence in these communi-
ties, and in natural habitats, such as mangroves, 
extends to their creation of strong micro- currents, 
flowing sometimes at over 180 µm sec −1 . These 
currents can bring nutrient-rich waters to the 
bacterial biofilm on the surface of which the 
 peritrichs are attached (Fried & Lemmer, 2003; 
Vopel, Reick, Arlt, Pohn, & Ott, 2002, Vopel, 
Thistle, Ott, Bright, & Roy, 2004). Even epibionts 
on turbellarians , such as Urceolaria mitra , feed 
on bacteria , chlorophytes , and chrysophytes 
(Reynoldson, 1955). Some peritrichs , particularly 
Ophrydium species, are known to harbor Chlorella
symbionts. Non-colonial Ophrydium can be domi-
nant ciliates in some lakes (Modenutti & Balseiro, 
2002) while the colonies of Ophrydium versatile
can be conspicuous components of the freshwater 
benthos (Duval & Margulis, 1995). Photosynthesis 
by the Chlorella symbionts of O. versatile is very 
efficient at low light levels and along with filter-
feeding by the ciliates produces carbon sufficient 
to maintain the growth rate of the colony (Sand-
Jensen, Pedersen, & Geertz-Hansen, 1997). 
 Scuticociliates , typified as downstream filter 
feeders (Fenchel, 1980a, 1980b), are typically the 
dominant bacterivorous ciliates in the hypolim-
nion of freshwater (Amblard, Sime-Ngando, 
Rachiq, & Bourdier, 1993; Carrias, Amblard, 
& Bourdier, 1998; Taylor & Heynen, 1987) and 
brackish environments (Dolan, 1991). A vari-
ety of bacterial species has been observed to be 
ingested by Cyclidium (Šimek, Macek, Pernthaler, 
Straškrabová, & Psenner, 1996; Taylor, 1979) and 
Uronema species (Christaki, Dolan, Pelegri, & 
Rassoulzadegan, 1998, Christaki, Jacquet, Dolan, 
Vaulot, & Rassoulzadegan, 1999; Hamilton & 
Preslan, 1969; Iriberri, Ayo, Santamaria, Barcina, 
& Egea, 1995; Parker, 1976). Ingestion can exceed 
500 bacteria per cell per hour for Cyclidium (Šimek 
et al., 1996). While Cinetochilum could ingest bac-
teria, its growth flourished on diatoms , dinophytes , 
 chrysophytes , cryptophytes , and chlorophytes 
(Šimek et al., 1995; Skogstad et al., 1987). The 
larger planktonic scuticociliate Histiobalantium
grows well on cryptophytes (Müller & Weiss, 
1994). As predicted by bead experiments (Fenchel, 
1980a, 1980b), Cyclidium does feed selectively 
on different-sized bacterial prey (Šimek, Vrba, 
& Hartman, 1994), and this can, in turn, influ-
ence size distribution of the bacterial community 
(Posch et al., 2001). Nevertheless, the situation is 
undoubtedly more complex. Sanders (1998) and 
Christaki et al. (1998, 1999) have demonstrated 
that the surface properties of particles can influ-
ence the ingestion rates of both freshwater and 
marine scuticociliates . 
 Oligohymenophoreans are some of the fastest 
growing ciliates, at least in the laboratory setting.
Tetrahymena under appropriate axenic culture 
conditions can achieve doubling times of less 
than 1.5 h (Orias et al., 2000). However, more 
typically the doubling time is around 5.5 h in 
 axenic proteose-peptone medium extending to 
8.5 h in bacterized medium (Taylor et al., 1976). 
The doubling times of other hymenostomes , such 
as Colpidium and Glaucoma species, on bacte-
rial prey achieve maxima around 2.5 h and 4 h, 
respectively (Taylor, 1978). Scuticociliates , such 
as Uronema , Parauronema , and Cyclidium , can 
achieve doubling times close to 2.5 h in the labo-
ratory setting, but typically exceed 4 h (Pérez-Uz, 
1995, 1996; Taylor). Laboratory growth rates 
can be significantly different among geographi-
cally diverse clones of Uronema , suggesting local 
physiological adaptation or genetic differentiation 
(Pérez-Uz, 1995). In contrast, growth rates of field 
populations of scuticociliates incubated over a 24-
h period tend to be much slower, indicating that 
natural food supplies likely limit growth (Macek, 
Šimek, Pernthaler, Vyhnálek, & Psenner, 1996). 
This difference also applies to laboratory and 
field populations of peritrichs , such as Vorticella , 
Epistylis , and Opercularia : doubling times in the 
laboratory can be around 1–2 h (Curds & Vandyke, 
1966) while estimates from field populations sug-
gest 8 h to be typical (Taylor, 1983b). The peni-
culine Paramecium can also achieve doubling 
times approaching 2 h in the laboratory setting 
(Curds & Vandyke, 1966). 
 Oligohymenophoreans , in addition to being effec-
tive predators on organisms ranging from bacteria 
to fish , are themselves also prey. Hymenostomes , 
such as Tetrahymena and Colpidium , are con-
sumed by copepods (Hartmann, Taleb, Aleya, & 
Lair, 1993; Kumar, 2003), cladocerans (Jack & 
Gilbert, 1993), rotifers (Gilbert & Jack, 1993), and 
 mosquito larvae (Addicott, 1974). Colpidium spe-
cies can escape predation by the macrostomatous 
 peniculine Lembadion by significantly transform-
ing their morphology, becoming more broad and 
almost spherical in shape (Fyda, 1998; Fyda, 
Kennaway, Adamus, & Warren, 2006). Peniculines , 
such as Paramecium and Frontonia , are consumed 
by rotifers (Maly, 1975), copepods (Hartmann 
et al., 1993), cladocerans (DeBiase, Sanders, & 
Porter, 1990; Jack & Gilbert), and mosquito larvae 
(Addicott, 1974). Peniculines are also the prey 
of other ciliates, such as the suctorian Podophrya
(Jurand & Bomford, 1965), a variety of litostomes 
(Harumoto & Miyake, 1991; Miyake & Harumoto, 
1996; Salt, 1974), and even larger colpodeans
(Foissner, 1993a; Salt, 1967). While the trichocyst 
 extrusomes of peniculines may not defend them 
against their metazoan predators, Paramecium
species obtain some defensive function from these 
organelles against some litostome predators, an 
exception being Didinium , the infamous predator 
of Paramecium (Harumoto, 1994; Harumoto & 
Miyake, 1991; Miyake & Harumoto; Sugibayashi 
& Harumoto, 2000). Even though some peritrichs 
can contract their stalks at up to 60 cm sec −1 (Lom, 
1994), they are still eaten. Peritrichs , such as 
Epistylis and Opercularia , show survivorships of 
about 50% per day (Taylor, 1983b), possibly due 
to predation by rotifers and oligochaetes (Kusuoka 
& Watanabe, 1989) and insects (Addicott, 1974). 
Their sessile nature makes them susceptible to other 
ciliates, such as the slow-moving pleurostome lito-
stomes (Canella, 1951; Foissner, 1983b), and even 
 hyphomycete “ fungi ” (Barron & Szijarto, 1982). 
Finally, scuticociliates are susceptible to predation 
by heliozoans (Pierce & Coats, 1999), copepods 
(Burns & Gilbert, 1993; Ederington, McManus, & 
Harvey, 1995), cladocerans (Wickham & Gilbert, 
1993), and mosquito larvae (Addicott). While it 
has not yet been supported empirically, the jumps 
and darts of some planktonic scuticociliates , like 
Cyclidium , may reduce their susceptibility to pre-
dation (Tamar, 1979), as has been demonstrated for 
 prostomes and oligotrichs (Jakobsen, 2001). 
 Oligohymenophoreans can also be infected or 
colonized by a variety of smaller organisms, rang-
ing from bacteria to other protozoa. The literature 
on these bacterial groups is extensive and is only 
briefly introduced here. Probably the best-known 
symbionts are the so-called “killer particles” of 
Paramecium , originally reported by Sonneborn 
(1938), they have now been assigned to the 
 alpha-proteobacterium genus Caedibacter (Pond, 
Gibson, Lalucat, & Quackenbush, 1989; Preer, 
Preer, & Jurand, 1974; Quackenbush, 1988; Fokin 
& Görtz, 1993) or to the gamma-proteobacteria