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are global. The limita-
tion of the symbiotic forms being the presence of 
their hosts, none of which occur in Antarctica but 
are present on every other continent. 
 Haptorians are predators of smaller protists, both 
autotrophic and heterotrophic flagellates, other 
 ciliates , and even small metazoans , such as rotifers . 
Common genera, such as Didinium , Monodinium , 
Mesodinium , Dileptus , and Lagynophrya , have 
been recorded from continental and coastal marine 
waters and sea ice of Antarctica (Garrison et al., 
2005; Leakey, Fenton, & Clarke, 1994; Petz & 
Foissner, 1997), North America (Dolan, 1991) and 
 Europe (Leakey, Burkhill, & Sleigh, 1993; Zingel, 
Huitu, Makela, & Arvola, 2002), deep waters of 
the Mediterranean Sea (Hausmann, Hülsmann, 
Polianski, Schade, & Weitere, 2002), temperate 
freshwater lakes in Europe (Carrias, Amblard, 
& Bourdier, 1994; Zingel & Ott, 2000), Asia 
(Obolkina, 2006), and North America (Hunt & 
Chein, 1983), reservoirs in South America (Barbieri 
& Orlandi, 1989), subtropical lakes in North 
America (Beaver & Crisman, 1982, 1989b), rivers 
(El Serehy & Sleigh, 1993; Foissner, 1997b), and 
ponds and streams (Domenech, Gaudes, Lopez-
Doval, Salvado, & Munoz, 2006; Foissner, 1980b; 
Madoni & Sartore, 2003). They are found as part of 
the interstitial fauna of marine shores (Al-Rasheid, 
1999) and are a conspicuous constituent of soils 
throughout the world (Berger, Foissner, & Adam, 
1984; Buitkamp, 1977; Foissner, 1998a; Petz & 
Foissner). Haptorians are often recorded from 
 anoxic sediments (Guhl, Finlay, & Schink, 1996; 
Madoni & Sartore, 2003). Environmental DNA 
analyses have even found Spathidium genes in a 
 cryoconite hole in the Canada Glacier , Antarctica 
(Christner, Kvitko, & Reeve, 2003). 
 Their numbers vary more erratically than their 
prey and they are typically not as abundant as this 
prey. They can achieve high densities: Didinium
can reach 2,800 l −1 (Dolan, 1991); Mesodinium
pulex over 2,000 l −1 (Barbieri & Orlandi, 1989); 
Askenasia stellaris and Lagynophrya over 1,000 l −1
(Leakey et al., 1993). Haptorians represented almost 
50% of the ciliate abundance at depths between 10 
and 15 m in some lakes (Carrias et al., 1994). They 
generally range from 5–30% of the abundance 
across lakes of differing trophic status, while their 
abundance is positively correlated with the trophic 
status of the lake (Beaver & Crisman, 1982). 
 Special mention should be made of the autotrophic 
 haptorian Myrionecta rubra (= Mesodinium 
rubrum ). This ciliate is host to a cryptophycean 
endosymbiont (see more below). This ciliate has 
been recorded in all the oceans of the world 
(Crawford, 1989; Lindholm, 1985), and in antarctic 
brackish and saline lakes (Laybourn-Parry, Quayle, 
& Henshaw, 2002; Perriss, Laybourn-Parry, & 
Marchant, 1995). Myrionecta is often restricted 
to a stratum or layer and may migrate vertically 
at least 10 m on a daily basis (Dale, 1987; Owen, 
Gianesella-Galvão, & Kutner, 1992). Two discrete 
cell sizes have been reported for Myrionecta , a 
larger form at colder times of the year and a smaller 
form at warmer times (Modigh, 2001; Montagnes 
& Lynn, 1989). Its abundances can be very high, 
ranging to over 30,000 l −1 (Edwards & Burkhill, 
1995; Sanders, 1995) so that it will cause red tides 
(Crawford, 1989; Lindholm, 1985; White, Sheath, 
& Hellebust, 1977). These abundances mean that 
M. rubra can make significant contributions to 
 primary production , sometimes well over 20% 
(Leppänen & Bruun, 1986; Sanders, 1995; Smith 
& Barber, 1979). 
 Trichostomes are endosymbiotic primarily in ver-
tebrates . The vestibuliferidan Balantidium has been 
reported from fish (Grim, 1989; Grim, Clements, 
& Byfield, 2002), frogs and toads (Affa’a, 1988a; 
Khan & Ip, 1986), turtles (Fenchel, 1980d; Geiman 
& Wichterman, 1937), ostriches and rheas (Gordo, 
Herrera, Castro, Buran, & Diaz, 2002), the caecum 
of a horse (Wolska, 1962), baboons and other pri-
mates , including humans (Müller-Graf, Collins, & 
Woolhouse, 1996; Zaman, 1978), and pigs (Zaman). 
A survey of recent reports of trichostomes provides 
the following brief synopsis. Some or all of buet-
schliids , isotrichids , paraisotrichids , blepharoco-
rythids , ophryoscolecids , and cycloposthiids have 
been reported recently from ruminants such as cattle
and sheep (Dehority, 1986; Gocmen, Dehority, 
Talu, & Rastgeldy, 2001; Imai, Han, Cheng, & 
Kudo, 1989, Towne & Nagaraja, 1990), the yak 
(Guirong, Su, Hua, Zhu, & Imai, 2000), water buffalo
(Dehority, 1979), bison (Towne, Nagaraja, & 
Kemp, 1988), musk oxen (Dehority, 1985), giraffe 
(Kleynhans & Van Hoven, 1976), and camel (Imai 
& Rung, 1990b). Ophryoscolecids , predominantly 
Entodinium species, and fewer dasytrichids , and 
 isotrichids are found in antelopes (Fernández-
Galiano & Campos, 1992; Imai & Rung, 1990a; 
Kleynhans, 1982; Van Hoven, 1983; Van Hoven, 
Hamilton-Attwell, & Grobler, 1978). Entodinium
species appear also to dominate the fauna in deer ,
 elk , and pronghorn antelope (Dehority, 1990, 1995; 
Ito, Imai, & Ogimoto, 1993) although isotrichids 
have also been reported (Imai et al., 1995). 
 Overall, the non-ruminant mammals harbor a 
much higher diversity of trichostomes , although 
one particular host species may have a limited 
diversity of ciliate species. Most is known about the 
endosymbionts in the colon of horses (Bonhomme-
Florentin, 1994; Grain, 1966a, 1994; Wolska, 1965).
 Buetschliids , hydrochoerellids , pycnotrichids , and 
 cycloposthiids have been recorded in the rodents , 
such as the South African mole rat (Sandon, 
1941b) and South American capybara (Ito & 
Imai, 2000a, 2000b). Ophyroscolecids were found 
in the collared peccary (Carl & Brown, 1983). 
 Buetschliids , paraisotrichids , blepharocorythids , 
and entodiniomorphids were recorded in the stom-
ach of the hippopotamus (Thurston & Grain, 
1971; Thurston & Noirot-Timothée, 1973). Some 
unusual cycloposthiids , rhinozetids , buetschliids , 
 paraisotrichids , blepharocorythids , and ditoxids 
have been recorded from the colon of rhinoc-
eros (Gilchrist, Van Hoven, & Stenson, 1994; 
Van Hoven, Gilchrist, & Hamilton-Attwell, 1987; 
Van Hoven, Gilchrist, & Hamilton-Attwell, 1988). 
 Buetschliids , paraisotrichids , ophryoscolecids , and 
 cycloposthiids have been observed throughout the 
 intestinal tract of elephants (Eloff & Van Hoven, 
1979; Timoshenko & Imai, 1997). Several very 
recent reports have described novel isotrichids , 
 cycloposthiids , and new families of macropo-
diniids from Australian macropodid marsupials 
(Cameron & O’Donoghue, 2003a; Cameron et al., 
2000, 2001a, 2001b; Dehority, 1996). Finally, 
 cycloposthiids and troglodytellids have been 
recorded in the feces of chimpanzees and gorillas 
(Freeman, Kinsella, Cipolletta, Deem, & Karesh, 
2004; Goussard, Collet, Garin, Tutin, & Fernandez, 
1983; Imai, Ikeda, Collet, & Bonhomme, 1991). 
 Except for the vestibuliferidan Balantidium , 
which can cause damage to the intestinal tract of 
 pigs and humans (Zaman, 1978), most trichostomes
are considered to be commensals. Indeed, non-
pathogenic Balantidium species likely feed on a 
variety of bacteria and flagellates , which cohabit 
the gut (Grim, 2006). Nevertheless, there has been 
debate about the role of the rumen ciliates in the 
biology of their hosts since their first discovery by 
Gruby and Delafond (1843). The rumen ecosystem 
is composed of a variety of bacterial species, fungi , 
a few flagellates , and a considerable diversity and 
abundance of ciliates. Ciliate abundances can range 
from 10,000 ml −1 of rumen fluid in yak (Guirong 
et al., 2000) and zebu (Bonhomme-Florentin, Blancou, 
& Latteur, 1978), to over 100,000 ml −1 in cattle 
and sheep (Imai et al., 1989), antelopes