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1990) to coastal waters in North America 
(Borror, 1963) to Antarctica (Thompson, 1972); in 
the psammobiotic communities of Europe and Asia 
(Agamaliev, 1968; Burkovsky, 1970; Fernández-
Leborans et al., 1999), including Arabia (Al-Rasheid,
1999d); in rivers and streams in Europe (Domenech 
et al., 2006; Foissner, 1997b; Komala & Przybos, 
1990) and Africa (Dragesco, 1972); in freshwater 
ponds in Europe (Finlay et al., 1979, 1988; Komala 
& Pryzbos, 1994; Kosciuszko & Prajer, 1991; 
Madoni & Sartore, 2003; Przybos & Fokin, 1997), 
and in Asia (Przybos, Fokin, Stoeck, & Schmidt, 
1999), including Arabia (Al-Rasheid, 1996); in 
 hypersaline lakes in Africa (Yasindi et al., 2002); 
and in freshwater lakes in Europe (Schlott-Idl, 
1984), in North America (Hunt & Chein, 1983), 
in Asia (James, Burns, & Forsyth, 1995; Obolkina, 
2006), and in Africa (Dragesco & Dragesco-
Kernéis, 1991). Peniculines are dominant in terms 
of abundance or biomass only in exceptional 
 circumstances. For example, on occasion, Yasindi 
et al. (2002) noted Frontonia species dominating 
the community of the alkaline saline Lake Nakuru . 
The planktonic taxon, Disematostoma , has been 
recorded to exceed 10,000 l −1 (Finlay et al., 1988) 
while its relative Stokesia rarely exceeds 100 l −1
(Hunt & Chein, 1983). 
 Hymenostomes are rarely recorded in gen-
eral surveys of habitats, suggesting that they are 
extremely patchy in their distributions and prob-
ably dependent upon high concentrations of bac-
teria associated with decaying organic matter . 
However, when appropriate sampling strategies are 
employed, Tetrahymena species have been recorded 
from the major continents (Elliott, 1973b; Simon 
et al., 1985). Lambornella species have been 
recorded from tree-hole habitats where they may 
parasitize mosquitoes (Washburn, Gross, Mercer, 
& Anderson, 1988), and a proposed new tetrahy-
menine genus, Bromeliophrya , has been found 
in water trapped in the leaf axils of bromeliads 
(Foissner et al., 2003). 
 While the above discussion has focused on free-
living oligohymenophoreans , there is a much more 
abundant literature that deals with those species as 
15.2 Life History and Ecology 289
symbionts on and in other organisms. We can only 
provide a narrow window onto this vast literature in 
providing below citations that indicate the breadth 
of these associations. If “ecological success” of 
members of the subclasses is judged by the num-
bers of species reported to establish symbioses, 
then members of the subclasses Scuticociliatia and 
 Peritrichia are by far the most successful as mem-
bers of both of these classes have been reported on 
the largest number of hosts. 
 Scuticociliates have been reported as symbi-
onts, for example: from both bivalve molluscs , 
such as Mytilus (Antipa & Dolan, 1985; Berger & 
Hatzidimitriou, 1978; Fenchel, 1965a), Macoma , 
Mya , (Fenchel, 1965a), Anodonta (Antipa & 
Small, 1971; Fenchel), Dreissena (Burlakova, 
Karatayev, & Molloy, 1998; Fenchel; Molloy, 
Karatayev, Burlakova, Kurandina, & Laruelle, 
1997), Crassostrea (Elston, Cheney, Frelier, & 
Lynn, 1999), and Teredo (Tuffrau & Laval-Peuto, 
1978), and gastropod molluscs , such as Littorina
(Fenchel; Fokin, 1993b), Oxychilus (Kazubski, 
1963) and Schistophallus (Kazubski, 1958); from 
 annelids , such as Laonome (Kozloff, 1965a), 
Drilocrius (Kozloff, 1965b), and Alma (Ngassam 
& Grain, 1997, 2002); from crustaceans , such 
as Cancer (Morado & Small, 1995; Morado, 
Giesecke, & Syrjala, 1999), Callinectes (Messick 
& Small, 1996), and Homarus (Cawthorn et al., 
1996) and Nephrops (Small, Neil, Taylor, Bateman, 
& Coombs, 2005); from echinoderms , such as 
Asterias (Bouland, de Puytorac, & Bricourt, 1987), 
Leptasterias (Stickle et al., 2001), Heliocidaris
and Hemicentrotus (Song, Wilbert, & Warren, 
1999), Arbacia and Paracentrotus (Foissner, 
1985c), and a broad diversity of echinoids (Levine, 
1972; Lynn & Berger, 1972, 1973; Poljansky 
& Golikova, 1959); and from a variety of fish 
species (Cheung, Nigrelli, & Ruggieri, 1980), 
including Dicentrarchus (Dragesco et al., 1995), 
Thunnus (Crosbie & Munday, 1999), Paralichthys
(Jee, Kim, & Park, 2001), Scophthalmus (Iglesias 
et al., 2001; Paramá et al., 2005), and Pampus (Azad, 
AL Marzouk, James, Almatar, & AL Gharabally, 
2007). The monographic treatments by Chatton 
and Lwoff (1949, 1950) and Raabe (1967, 1970a, 
1970b, 1971b, 1972) are still extremely valuable 
 In the majority of cases, scuticociliates are 
“harmless” commensals . However, in some cases, 
they can cause significant harm as opportunistic 
pathogens of wild and cultured organisms. The 
condition, termed scuticociliatosis , has caused 
significant mortalities in wild crab (Morado 
et al., 1999), lobster (Cawthorn et al., 1996), 
and starfish (Leighton, Boom, Bouland, Hartwick, 
& Smith, 1991) populations, and several spe-
cies held in aquaculture operations, including 
 oysters (Elston et al., 1999) and several species 
of fishes (Alvarez-Pellitero et al., 2004; Azad 
et al., 2007; Dragesco et al., 1995; Iglesias et al., 
2001; Jee et al., 2001). The ciliates appear to 
enter the fish hosts, at least, through lesions in 
the gills and skin (Paramá et al., 2003), and are 
particularly strongly attracted to blood and serum
from infected fish (Paramá, Iglesias, Álvarez, 
Sanmartín, Leiro, 2004). Infections can be control-
led potentially by formalin , malachite green , UV 
irradiation , nicolsamide , and polyphenols (Crosbie 
& Munday, 1999; Iglesias, Paramá, Alvarez, Leiro, 
& Sanmartín, 2002; Kasai, Osawa, Kobayashi, & 
Yoshimizu, 2002; Leiro, Arranz, Parama, Alvarez, 
& Sanmartin, 2004). 
 Peritrichs , in addition to being the most speciose 
group in the Class OLIGOHYMENOPHOREA , 
are by far the most successful symbionts. This is 
undoubtedly due in part to their ability to attach 
to a variety of substrates: sessiline peritrichs use 
the scopula , while mobiline forms use their adhe-
sive disk (Lom, 1994). The scopula may secrete 
substances to aid attachment to the host surface 
or may have specialized cilia that enable attach-
ment (Lom & Corliss, 1968). The literature on the 
group is enormous, and their ability to colonize 
other organisms has been well known (Nenninger, 
1948; Stiller, 1941, 1971). Peritrichs have been 
reported as symbionts, both as ectocommensals 
and endocommensals, for example: mobiline peri-
trichs in turbellarians (Ball & Fernando, 1968; 
Reynoldson, 1956); mobiline peritrichs in molluscs , 
both marine (Cremonte & Figueras, 2004; Fenchel, 
1965a; Van As & Basson, 1993; Xu, Song, & 
Warren, 2000), freshwater (Raabe & Raabe, 1961), 
and terrestrial (Kazubski, 1981; Raabe & Raabe; 
Sirgel, 1983), and sessiline peritrichs in molluscs 
(Botes, Basson, & Van As, 2001a; Hu & Song, 
2001c; Lom & Corliss); sessiline peritrichs on the 
adults and eggs of rotifers whose fecundity was 
decreased by this colonization (Gilbert & Schröder, 
2003; Regali-Selghim & Godinho, 2004); sessiline 
 peritrichs on copepod nauplii whose survival rates 
were lowered (Weissman, Lonsdale, & Yen, 1993); 
 sessiline peritrichs on insects (Jilek, 1980; Matthes, 
1974, 1990; Matthes & Guhl, 1975; Guhl & 
Haider, 1988); mobiline peritrichs on the spines of 
 sea urchins (Beers, 1966b); mobiline peritrichs on 
 ctenophores (Moss, Estes, Muellner, & Morgan, 
2001); mobiline peritrichs as epibionts on tadpoles 
(Kazubski, 1988) and in the urinary bladder of 
adult anurans (Kazubski, 1980; Bank, Basson, & 
Van As, 1989) and urodeles (Kazubski, 1979). The 
unusual sessiline peritrich Ellobiophrya clasps the 
ciliated tentacles of marine ectoprocts with its arm-
like holdfast (Clamp, 1982). Ellobiophrya species