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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 \u22121 (Finlay et al., 1988) while its relative Stokesia rarely exceeds 100 l \u22121 (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 289 290 15. Subphylum 2. INTRAMACRONUCLEATA: Class 9. OLIGOHYMENOPHOREA 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 \u201cecological success\u201d 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 resources. In the majority of cases, scuticociliates are \u201charmless\u201d 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