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, the Hoplitophryidae , the Intoshellinidae , 
the Maupasellidae , and the Radiophryidae . Affa’a, 
Hickey, Strüder-Kypke, and Lynn (2004) have 
presented the only molecular genetic evidence that 
confirms the placement of the astome Anoplophrya
within the Class OLIGOHYMENOPHOREA . As 
with the thigmotrichs , monographic work on 
the group is now well over 30 years old (e.g., 
Corliss, de Puytorac, & Lom, 1965; de Puytorac, 
15.1 Taxonomic Structure 287
1954, 1957, 1960, 1961, 1970, 1972), but see de 
Puytorac (1994g) for an update. 
 In conclusion, molecular phylogenies 
of SSUrRNA, LSUrRNA, and some proteins 
strongly support the monophyly of the Class 
 OLIGOHYMENOPHOREA and the subclasses 
of predominantly free-living ciliates assigned to 
it. We await anxiously the results of more com-
prehensive analyses of gene sequences for repre-
sentatives of the astomes and the apostomes , both 
to confirm preliminary results of their assignment 
to this class and to determine if each subclass is 
indeed monophyletic. 
 15.2 Life History and Ecology 
 It almost goes without saying that the ciliates 
in this class are broadly distributed throughout 
the world. For those species that are symbionts, 
both ectosymbionts and endosymbionts , their 
distribution is determined by that of their host or 
hosts. This would include all the species in the 
subclasses Astomatia and Apostomatia , a large 
number of species of peritrichs , including all 
 mobilid peritrichs , a few species of scuticociliates 
and hymenostomes , and a rare species of peni-
culine (Maguire & Belk, 1967). Representatives 
of the subclasses Scuticociliatia , Peniculia , and 
 Peritrichia are often reported as conspicuous 
members of free-living assemblages of ciliates, 
while hymenostomes are less often conspicuous. 
 Oligohymenophoreans have some of the most 
complex life cycles among the ciliates (Fig. 15.1; 
see also Figs. 3.1, 4.4). 
 Scuticociliates , typically Cyclidium and 
Pleuronema species, have been found: in soils 
and mosses in Europe (Foissner, 1981a; Grolière, 
1975c), South America (Steffens & Wilbert, 2002), 
 Africa (Buitkamp, 1977; Steffens & Wilbert), and 
 Antarctica (Ryan et al., 1989); in temporary ponds 
in Latin America (López-Ochoterena, 1966) and 
 Antarctica (Thompson, 1972); in marine plankton, 
especially of coastal regions, in North America 
(Borror, 1963; Dolan, 1991), Latin America (Bulit, 
Díaz-Avalos, Signoret, & Montagnes, 2003; 
Silver, Gowing, Brownlee, & Corliss, 1984), in 
 Europe (Edwards & Burkhill, 1995), sometimes as 
deep as 900 m (Hausmann, Hülsmann, Polianski, 
Schade, & Weitere, 2002), and in Antarctica (Song 
& Wilbert, 2000b); in marine sands as interstitial 
fauna from Western Europe (Dragesco, 1963; 
Fernández-Leborans & Fernández-Fernández, 
1999; Fernández-Leborans, Valgañon, & Castro 
de Zaldumbide, 1999), from Eastern Europe 
(Agamaliev, 1971; Burkovsky, 1970; Kovaleva & 
Golemansky, 1979), and the Arabian Gulf (Al-
Rasheid, 1999c); in hypersaline and solution lakes 
in Europe (Dyer, 1989; Esteban, Finlay, & Embley, 
1993a), Africa (Yasindi, Lynn, & Taylor, 2002), and 
 Australia (Post, Borowitzka, Borowitzka, Mackay, 
& Moulton, 1983); in leaf litter in mangrove for-
ests in Asia (Dorothy, Satyanarayana, Kalavati, 
Raman, & Dehairs, 2003); in streams and rivers in 
 Europe (Cleven, 2004; Domenech, Gaudes, Lopez-
Doval, Salvado, & Munoz, 2006; Foissner, 1997b; 
Madoni & Ghetti, 1980); in freshwater ponds in 
 Europe (Finlay et al., 1988; Madoni & Sartore, 2003)
and North America (Wickham & Gilbert, 1993); 
and in freshwater lakes in Europe (Carrias, 
Amblard, & Bourdier, 1994; Finlay, Bannister, & 
Stewart, 1979; Schlott-Idl, 1984; Skogstad, Granskog,
& Klaveness, 1987; Zingel & Ott, 2000; Zingel, 
Huitu, Makela, & Arvola, 2002), in North America 
(Beaver & Crisman, 1982, 1989b), and Asia 
(Obolkina, 2006; Song, 2000), often in the anoxic 
 hypolimnion (Guhl, Finlay, & Schink, 1996). 
Cyclidium and other oligohymenophoreans have 
been recorded in the fluid from pitcher plants on 
three continents, Eurasia , North America , and 
 Australia (Cochran-Stafira & von Ende, 1998; 
Rojo-Herguedas & Olmo, 1999) and bromeli-
ads in Central and South America (Foissner, 
Strüder-Kypke, van der Staay, Moon-van der Staay, 
& Hackstein, 2003). 
 Scuticociliates are typically microphagous bac-
terivores, consequently they are often more abun-
dant in eutrophic habitats (Beaver & Crisman, 
1982), achieving abundances of almost 40,000 l −1
in freshwater lakes (Song, 2000). In lakes and 
coastal marine habitats, they are often most com-
mon in the deeper waters (Zingel & Ott, 2000), 
often at or below the oxycline (Finlay & Maberly, 
2000; Fenchel, Kristensen, & Rasmussen, 1990; 
Fenchel et al., 1995; Taylor & Heynen, 1987). 
These ciliates may first become associated with 
sinking detritus on which bacteria are growing 
(Silver et al., 1984) or they may be growing in situ 
in the water column where bacterial abundances 
may be higher (Fenchel et al., 1990). 
 Peritrichs , typically assigned to the genus 
Vorticella , are the second most abundant oligo-
hymenophorean group recorded from a variety of 
habitats. They have been found: in soils and mosses 
in Europe (Foissner, 1981a) and Antarctica (Ryan 
et al., 1989); in permanent and temporary ponds 
in Europe and North America (Madoni & Sartore, 
2003), Latin America (López-Ochoterena, 1966), 
and Antarctica (Thompson, 1972); in coastal marine 
habitats, primarily attached to substrates, in North 
America (Beech & Landers, 2002; Borror, 1963; 
Landers & Phipps, 2003), in Asia (Dorothy et al., 
2003), and Antarctica (Song & Wilbert, 2002); in 
rivers and streams, attached to substrates, in Europe 
(Cleven, 2004; Foissner, 1997b; Harmsworth 
& Sleigh, 1993), North America (Small, 1973; 
Taylor, 1983a), and Asia (Kusuoka & Watanabe, 
1987), and also in the plankton in Europe (Balazi & 
Matis, 2002) and North America (Clamp & Coats, 
2000); in freshwater ponds in Europe (Finlay et al., 
1988) and Arabia (Al-Rasheid, 1996); and in the 
pelagial of freshwater lakes in Europe (Foissner, 
1979d; Packroff, 2000; Zingel & Ott, 2000), North 
America (Beaver & Crisman, 1989b; Kerr, 1983), 
 South America (Barbieri & Orlandi, 1989), and 
 Asia (Obolkina, 2006; Song, 2000). 
 Pelagic peritrichs may not be free-swimming, 
but rather are attached to filamentous algae 
(Davis, 1973; Kerr, 1983; Pratt & Rosen, 1983). 
 Abundances of peritrichs are not often reported, and 
when planktonic , are difficult to interpret because 
they are often attached to algae in the plankton . 
They can attain abundances exceeding 2,000 l −1
in freshwater habitats, growing on colonies of 
Microcystis and Nostoc (Barbieri & Orlandi, 1989; 
Kerr, 1983). Freshwater species of Carchesium and 
Vorticella have been recorded to exceed 1,000 cm −2
and 100 cm −2 respectively (Kusuoka & Watanabe, 
1987), but total peritrich communities are typically 
below 50 cm −2 on benthic substrates (Harmsworth 
& Sleigh, 1992, 1993). In marine habitats, colo-
nization of artificial substrates by peritrichs can 
achieve densities exceeding 5,000 cm −2 , but typi-
cally abundances are well below 1,000 cm −2 (Beech 
& Landers, 2002; Landers & Phipps, 2003). 
 Peniculines , typically assigned to the genera 
Frontonia , Paramecium , and more rarely Stokesia , 
have often been reported from a variety of habi-
tats around the world, and are rarely more abun-
dant than representatives from the previous two 
subclasses. Peniculines have been found – in 
 soils from South America and Africa (Steffens 
& Wilbert, 2002); in temporary ponds from Latin 
America (López-Ochoterena, 1966); in marine 
habitats, from the water column in Europe (Fenchel 
et al.,