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tomont (Dickerson & Dawe, 1995; Ewing & Kocan, 
1992) (Fig. 15.1). The theront contacts the host 
 epithelium or gill tissue and penetrates between 
cells to enter the epidermis (Ewing, Kocan, & 
Ewing, 1985; Kozel, 1986). Fish hosts can be 
 immunized against “Ich” using the surface immo-
bilization antigen of the ciliate (Buchmann, Sigh, 
Nielsen, & Dalgaard, 2001; Wang & Dickerson, 
2002; Xu, Klesius, & Panangala, 2006). While 
 malachite green and formalin have long been 
effective treatments, both have carcinogenic prop-
erties. Malachite green has already been banned 
on fish farms in some countries. The search for 
other effective treatment compounds has included 
 sodium percarbonate , garlic extract , triazinone , 
and crude extracts of plants (Buchmann, Jensen, & 
Kruse, 2003; Ekanem, Obiekezie, Kloas, & Knopf, 
2004; Schmahl et al., 1989). 
 Apostomes have been reported as commensal 
symbionts, primarily from crustaceans (Bradbury, 
1996; Chatton & Lwoff, 1935a). Their life cycles 
are complex and varied (Fig. 3.1). One group, 
represented by species of Hyalophysa and 
Gymnodinioides , is termed exuviotrophic because 
they excyst to feed on the exuvial fluids in the host
moult, often increasing their body volume 60-fold 
before they encyst , divide, and disperse to find 
another host (Bradbury, 1966a; Grimes, 1976; 
Landers, Confusione, & Defee, 1996). A sec-
ond group, represented by Terebrospira , burrows 
through the endocuticle of the host shrimp and 
ingests the dissolved products (Bradbury, Clamp, 
& Lyon, 1974; Debaisieux, 1960). A third group, 
represented by Vampyrophrya , ingests tissues of 
the host calanoid copepod , either when it is injured 
or ingested (Grimes & Bradbury, 1992). A fourth 
group, represented by Collinia , lives endoparasiti-
cally in the body fluids of euphausiid crustaceans 
(Capriulo & Small, 1986; Lindley, 1978), and can 
cause mass mortalities of their hosts (Gómez-
Gutiérrez, Peterson, De Robertis, & Brodeur, 2003; 
Gómez-Gutiérrez, Peterson, & Morado, 2006). 
Two other, highly unusual members of the subclass 
are the pilisuctorids Conidophrys and Askoella , 
which attach to the setae of the host crustacean 
(Bradbury, 1975; Mayén-Estrada & Aladro-Lubel, 
2004), and the cyrtocarid Cyrtocaryum , which 
lives in the digestive caeca of polychaete annelids 
(Fauré-Fremiet & Mugard, 1949b). A final example 
are the chromidinid apostomes , which were studied 
by Chatton and Lwoff, and have been recently 
reported from the kidneys of Japanese cephalopods
(Furuya, Ota, Kimura, & Tsuneki, 2004). 
 Astomes are obligate commensal symbionts, 
found typically in the digestive tract of annelids (de 
Puytorac, 1994g). Cépède (1910) and de Puytorac 
(1954) stand as the substantial 20th century 
monographic works on this group. Despite these 
intensive investigations with reports from Europe 
(Cépède; de Puytorac), North America (Bush, 
1934; Powders, 1970), and Africa (de Puytorac & 
Dragesco, 1969a, 1969b; Ngassam, 1983), we still 
do not know how these ciliates are transmitted from 
one host to the next. They display a variety of cel-
lular differentiations, such as hooks and suckers , to 
maintain their position in the intestine (de Puytorac, 
1994g). The distribution of species of Maupasella , 
Anoplophrya , and Metaradiophrya along the diges-
tive tract of their host worm Allolobophrya savigni
is correlated with pH : each species apparently 
preferring a region characterized by a different 
 pH (de Puytorac & Mauret, 1956). Cepedietta
species are found in the intestine of salamanders , 
and their prevalence is inversely related to alti-
tudes below 1,400 m, perhaps explained by tem-
perature variations (Powders, 1970). There is yet 
no experimental evidence on how astomes feed. 
However, it is likely that they use receptor-mediated 
endocytosis , perhaps at the parasomal sacs , as has 
been demonstrated for Tetrahymena (Nilsson & van 
Deurs, 1983) and Paramecium (Allen, Schroeder, 
& Fok, 1992; Ramoino et al., 2001). 
 While we can only speculate at the moment on 
the feeding habits and preferences of astomes , 
there is no doubt that most free-living oligohy-
menophoreans are bacterivorous, down-stream 
filter feeders . The cilia of the paroral or undu-
lating membrane typically are used to filter the 
water from the feeding current created by the oral 
polykinetids (Fenchel, 1980a, 1980b), although 
species without well-developed paroral cilia, such 
as Glaucoma species, may use the innermost 
oral polykinetid as the filter (Fenchel & Small, 
1980). Hymenostomes , such as species in the 
genera Colpidium , Glaucoma , and Tetrahymena , 
can ingest a variety of bacterial species, which 
vary in how well they support growth (Dive, 
1973; Taylor, 1979; Taylor & Berger, 1976; 
Taylor, Gates, & Berger, 1976). Colpidium (or 
Dexiostoma ) and other hymenostomes may also 
supplement their diet with small detrital parti-
cles (Posch & Arndt, 1996). Tetrahymena may 
be a poor competitor in relation to Colpidium
or Paramecium (Long & Karel, 2002). This 
may explain the selection for histophagous 
and endoparasitic feeding strategies in some 
Tetrahymena species (Corliss, 1972c; Roque, de 
Puytorac, & Savoie, 1971), although glaucomids , 
such as Espejoia , have also adopted histophagy , 
feeding on and in the gelatinous matrices of egg 
masses of aquatic insects and molluscs (Fryd-
Versavel, Iftode, & Wilbert, 1975). Cannibalism 
has also evolved in Tetrahymena with species 
like Tetrahymena vorax and Tetrahymena patula
able to respond to secretions from prey species 
and develop into large-mouthed or macrostome 
predators able to feed on smaller Tetrahymena
species (Buhse, 1967; Corliss, 1973; Williams, 
1960, 1961). Furthermore, macrostome forms of 
T. vorax appear to be highly selective feeders, pre-
ferring to ingest T. thermophila over latex beads 
and microstome forms of T. vorax (Grønlien, 
Berg, & Løvlie, 2002). 
 Peniculine feeding preferences range from bacte-
rivory to mixotrophy . The peniculine Paramecium
feeds on a variety of bacterial species, although 
some bacterial species may be toxic (Curds & 
Vandyke, 1966). Paramecium may also supplement 
15.2 Life History and Ecology 293
its diet by ingesting detrital particles (Posch & 
Arndt, 1996). Paramecium bursaria typically hosts 
endosymbiotic Chlorella species ( see below ), and 
these influence the emphasis on bacterivory: in the 
dark P. bursaria relies on bacterivory , but in the 
light the predominant nutritional source derives 
from the photosynthetic products of its symbionts 
(Weis, 1974). However, Berk, Parks, and Ting 
(1991) observed that light itself may enhance 
 ingestion rates since mixotrophic P. bursaria fed 
faster than aposymbiotic individuals. As an aside, 
Chlorella -bearing P. bursaria are not ingested by 
Didinium as rapidly as apochlorotic individuals, 
suggesting that metabolites from the consortium 
may discourage predation (Berger, 1980). On the 
other hand, species of the peniculine Frontonia are 
typically not bacterivorous, but flourish on chryso-
phytes , cryptophytes , chlorophytes , diatoms , and 
even testate amoebae (Dias & D’Agosto, 2006; 
Skogstad et al., 1987). Carnivorous peniculines 
include the giant Neobursaridium , first classified 
as a heterotrich because of its large size and con-
vergently arranged somatic cilia that appeared 
like an adoral zone (Dragesco & Tuffrau, 
1967; Nilsson, 1969), and Lembadion , which 
can adjust its size to the size of its prey, such as 
Colpidium and Paramecium (Fyda, 1998; Kopp 
& Tollrian, 2003). 
 Peritrichs , such as Vorticella , Epistylis , and 
Zoothamnium , are very efficient downstream filter 
feeders (Fenchel, 1980a, 1980b; Sleigh & Barlow,