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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 \u22121 (Dolan, 1991); Mesodinium pulex over 2,000 l \u22121 (Barbieri & Orlandi, 1989); Askenasia stellaris and Lagynophrya over 1,000 l \u22121 (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\u201330% 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 \u22121 (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\u2019a, 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\u2019Donoghue, 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 \u22121 of rumen fluid in yak (Guirong et al., 2000) and zebu (Bonhomme-Florentin, Blancou, & Latteur, 1978), to over 100,000 ml \u22121 in cattle and sheep (Imai et al., 1989), antelopes