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can also be hypersymbionts , clasping scyphidiid 
 peritrichs that in their turn are ectosymbionts of 
 gastropods (Botes, Van As, Basson, & Van As, 
2001b; Peters, Van As, Basson, & Van As, 2004). 
The tips of these arms overlap in a structure called 
the bouton , whose substructure carries vesicles 
and microtubules similar to those of the scopula 
(Bradbury & Clamp, 1991). 
 Crustaceans and fishes are by far the most 
commonly reported hosts of peritrichs . There are 
several comprehensive reviews of the epibionts of 
 crustaceans (Fernández-Leborans & Tato-Porto, 
2000c; Morado & Small, 1995). Briefly, peritrichs , 
typically sessiline and loricate forms, have been 
reported on every major group of crustaceans for 
almost every place their hosts can be found: on 
 cladocerans (Green, 1974; Regali-Seleghim & 
Godinho, 2004); on ostracods (Griffiths & Evans, 
1994; Matthes, 1990); on copepods (Basson & 
Van As, 1991; Nagasawa, 1988; Regali-Seleghim 
& Godinho, 2004; Valbonesi & Guglielmo, 1988) 
whose fecundity may not be decreased (Xie, 
Sanderson, Frost, & Magnuson, 2001); on mysids 
(Fernández-Leborans, 2003); on amphipods 
(Clamp, 1990, 1991; Fenchel, 1965b; Fernández-
Leborans, Arndt, & Gabilondo, 2006; Jankowski, 
1997); on isopods (Cook, Chubb, & Veltkamp, 
1998; Ólafsdóttir & Svavarsson, 2002); and on 
 decapods (Clamp, 1992; Fernández-Leborans & 
Gabilondo, 2006; Mayén-Estrada & Aladro-Lubel, 
2002; Sprague & Couch, 1971). The prevalence 
and intensity of infection in aquaculture opera-
tions have been correlated with water quality : 
Zoothamnium increased and Cothurnia decreased 
as ectosymbionts of prawns as the water quality 
decreased (Hudson & Lester, 1992). Formalin 
treatment of cultured marine shrimps reduced peri-
trich infections (Bell, Arume, & Lightner, 1987). 
 Peritrich symbionts of fishes , dominated by 
the mobiline trichodinids , are primarily restricted 
to the skin and gills (Lom, 1995; Lom & Laird, 
1969), although sessiline peritrichs have also been 
reported (Chernyshova, 1976; Lom, 1966, 1973a, 
1995; Fitzgerald, Simco, & Coons, 1982). Reviews 
of these fish parasites , listing or briefly describing 
numerous species, have been provided by Hoffman 
(1988), Basson and Van As (1989), Van As and 
Basson (1989), and Lom (1995). Lom (1958) 
provided a uniform approach to the characteriza-
tion of mobiline peritrich species, which is now 
the standard approach for measuring the denti-
cles in the adhesive disk (but see also Van As & 
Basson, 1989). Numerous surveys of the skin and 
 gills of marine and freshwater fish demonstrate 
that trichodinids are particularly widespread parasites, 
being found in Europe (Arthur & Lom, 1984a; 
Dobberstein & Palm, 2000; Gaze & Wootten, 1998; 
Kazubski, 1991), Asia (Xu, Song, & Warren, 2002), 
 Africa (Al-Rasheid, Ali, Sakran, Baki, & Ghaffar, 
2000; Van As & Basson, 1992), North America , 
including the Caribbean (Arthur & Lom, 1984b; 
Arthur, Cone, Cusack, Barker, & Burt, 2004; Li & 
Desser, 1983), and the Pacific Ocean (Stein, 1979). 
 Trichodinids have also been found in the urinary 
system (Basson, 1989) and intestine (Basson, 
Van As, & Fishelson, 1990) of fishes . There are 
rare reports of epidemic trichodinosis in natural 
fish populations, perhaps under stress (Do Huh, 
Thomas, Udomkusonsri, & Noga, 2005). However, 
Trichodina species typically have been recorded 
in aquaculture operations worldwide, parasitizing 
farmed (Arthur & Margolis, 1984; Basson & Van 
As, 1994; Lom, 1994; Özer, 2000; Urawa, 1992) 
and ornamental (Hoffman, 1988; Thilakaratne, 
Rajapaksha, Hewakopara, Rajapakse, & Faizal, 
2003) fishes , and causing the disease trichodinosis . 
 Triazinone at a dose of 50 µg ml −1 was effective 
at reducing parasitemia on several fish species 
(Schmahl, Mehlhorn, & Taraschewski, 1989). 
 Peniculines , to our knowledge, have been 
reported as symbionts on only two occasions. 
Maguire and Belk (1967) reported Paramecium
in snails while Singh and Dash (1992) reported 
an infection of Paramecium in the urinary tract 
of a patient on dialysis. However, the cytological 
evidence showing a seemingly small ciliate with a 
15.2 Life History and Ecology 291
posterior contractile vacuole and a somewhat pyri-
form body shape, suggests that it might have been 
a hymenostome. 
 Few hymenostomes have been reported as symbi-
onts, with species in the three genera, Tetrahymena , 
Ophryoglena , and Ichthyophthirius being the most 
commonly reported. Tetrahymena species have 
been reported infecting natural populations of 
 platyhelminthes (Wright, 1981), gastropod molluscs
(Kazubski, 1964; Kozloff, 1956), and a variety 
of kinds of insects , such as black flies (Batson, 
1983; Lynn, Molloy, & Lebrun, 1981), mosqui-
toes (Barros et al., 2006; Clark & Brandl, 1976; 
Corliss & Coats, 1976; Egerter & Anderson, 1985; 
Jerome et al., 1996), chironomids (Corliss, 1960b;
Corliss, Berl, & Laird, 1979; Golini & Corliss, 
1981), and megalopterans (Batson, 1985), and 
aquarium or aquacultured fishes (Astrovsky et al., 
2002; Ferguson, Hicks, Lynn, Ostland, & Bailey, 
1987; Hatai et al., 2001; Hoffman et al., 1975; 
Imai, Tsurimaki, Goto, Wakita, & Hatai, 2000). 
Tetrahymena has infected a broader array of organ-
isms in experimental situations (Thompson, 1958), 
and it is likely that it is only a facultative parasite 
in nature (Corliss, 1960b, 1972c). Nevertheless, in 
some situations, these ciliates may cause signifi-
cant mortality of their insect hosts (Barros et al.; 
Grassmick & Rowley, 1973; Zaritsky, Ben-Dov, 
Zalkinder, & Barak, 1992). Could they be used as 
 biocontrol agents for these vectors of important 
human diseases? The relationship between the 
predator-host mosquito and its ciliate symbiont is 
intimate enough to have evolved a predator-induced 
chemical signal that causes the free-living “symbi-
onts” to transform as parasites, ultimately killing 
their host (Washburn et al., 1988). As a taxonomic 
aside, this tetrahymenid associated as a cuticular 
cyst on mosquitoes (Corliss & Coats, 1976; Egerter 
& Anderson, 1985) has been assigned to the genus 
Lambornella , although recent molecular evidence 
suggests that this genus rank is probably not justi-
fied (Strüder-Kypke et al., 2001). 
Ophryoglena species are typically characterized 
as histophagous on moribund and dead aquatic 
organisms (Mugard, 1949), although they have 
been found infecting living bivalves (Karatayev, 
Burlakova, Molloy, Volkova, & Volosyuk, 2002; 
Molloy, Lynn, & Giamberini, 2005) and insects 
(Gaino & Rebora, 2000) (Fig. 15.1). There is now 
evidence that parasitic Ophryoglena have been very 
recently introduced to Ireland with their bivalve 
hosts, likely by humans from mainland Europe 
(Burlakova et al., 2006). Undoubtedly the most 
infamous ophryoglenine ciliate is Ichthyophthirius 
multifiliis , the causative agent of white spot disease 
of fishes. There is an extensive literature on this 
ciliate (see Dickerson & Dawe, 1995; Matthews, 
2005). “Ich” is apparently attracted to host fish by 
 serum factors in their mucus (Buchmann & Nielsen, 
1999; Haas, Haberl, Hofmann, Kerschensteiner, & 
Ketzer, 1999), and can cause significant mortalities 
in aquaculture operations (e.g., Munderle, Sures, & 
Taraschewski, 2004). To our knowledge, only one, 
natural, mass mortality has ever been reported dur-
ing which over 18 million killifish in Lake Titicaca 
were killed (Wurtsbaugh & Tapia, 1988). However, 
“Ich” infections can impact the swimming speed 
of eels and, while not killing them, may affect 
their ability to reach spawning sites in early spring 
(Münderle, Sures, & Taraschewski, 2004). The 
dispersal or theront stage of the life cycle arises 
by multiple palintomic divisions from an encysted