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1988; Kazubski & Miga\u142a, 1974; Lom, 1995; Lom & Nigrelli, 1970; Urawa, 1992). Some unu- sual species have even invaded other vertebrates: Kyaroikeus species are found in the respiratory tracts of several species of odontocete cetaceans (Sniezek et al., 1995). Chonotrichs as ectosymbionts of crustaceans , are probably restricted in their distribution by the distribution of their hosts. However, our knowledge of these ciliates is fragmentary. Most species are found on the mouth parts and gills of marine crusta- ceans and have been found on crustaceans in all the world\u2019s oceans (for some examples, see Fernández- Leborans & Gabilondo, 2006; Fernández-Leborans & Sorbe, 1999; Jankowski, 1973b; Mohr et al., 1970; Morado & Small, 1995). The review by Fernández-Leborans (2001) provides a good entry into the literature. Chonotrich species appear to show very high site specificity to their host and even a particular body region on the host, although experimentation has yet to confirm this conclusion (Jankowski, 1973b). Spirochona , Cavichona , and Serpentichona , the only freshwater chonotrichs , typically infest the gills of freshwater gamma- rid amphipods worldwide (Fernández-Leborans, 2001; Jankowski, 1973b; Mohr et al.; Stloukal & Matis, 1993). Isochonids are hyperparasites, found on the copepod Balaenophilus , which itself is a parasite of baleen whales ! Batisse (1994a) noted that chonotrichs are very delicate ciliates, which do not survive long without their hosts and even when the host is removed from its natural habitat. Consequently, our knowledge of their natural his- tory is quite limited. The swarmers or buds are undoubtedly the dispersal phase, distributing the species over the host as colonization proceeds and distributing the species between hosts. When hosts are moulting , polygemmy or repeated budding without intervening growth may occur, providing many propagules likely to increase the chances of recolonization of the newly moulted host (Batisse, 1994a). Observations suggest that chonotrichs are omnivorous ciliates, feeding on tissue debris, cuti- cle pieces, bacteria , diatoms , and other protists. However, some chonotrichs can be quite selective, preferring bacteria and other protists (Batisse, 1994a). There has been no experimentation to sup- port this observations. Rhynchodians show two different life histories, conforming to the two major taxonomic groups into which they are divided. Both groups feed using their tentacle-like mouthparts, probably consuming prey cytoplasm. The hypocomatids blur the distinc- tion between predator and parasite, for they feed upon suctorians and peritrichs that are often larger than themselves and some species are found as parasites in ascidians (Burreson, 1973; Chatton & Lwoff, 1939b) and barnacles (Jankowski, 1967c). Hypocomatid -like ciliates were likely ancestors to the rhynchodids , which are all obligate para- sites. Rhynchodids typically parasitize marine and freshwater bivalve molluscs (Bower & Meyer, 1993; Dobrza ska, 1959, 1961, Molloy, Karatayev, Burlakova, Kurandina, & Laruelle, 1997; Raabe, 1970b), but they have also been reported on chi- tons , gastropods , and even sabellid polychaete annelids (Kozloff, 1961, 1965a). Host specificity of rhynchodids can be quite strict and there is even demic variation among ciliates isolated from individuals of the same host species (de Puytorac, 1994b). Adjacent hosts are likely infected by cili- ates that swim from one host to the next (Chatton & Lwoff, 1950; Fenchel, 1965a). Nevertheless, infections by rhynchodids rarely reach intensities that cause harm to their hosts. Suctorians attach to the substratum by a non- contractile stalk or directly by the body. The proteina- ceous materials used for attachment are extremely resistant to mechanical and chemical degradation (Batisse, 1994b). The substrate may be a biofilm on 10.2 Life History and Ecology 217 218 10. Subphylum 2. INTRAMACRONUCLEATA: Class 4. PHYLLOPHARYNGEA an inorganic substrate, on aquatic plants, or on the body surface of animals. Thus, suctorians can be both free-living or symbiotic, and are probably the most widespread symbiotic group in the phylum. They are found in marine and freshwater habitats, in soils and mosses and have been recorded on all continents (e.g., Collin, 1912; López-Ochoterena, 1966; Wang, 1977). There are also some species that are found in the plankton . Symbiotic spe- cies are often found on crustaceans (Fernández- Leborans & Tato-Porto, 2000a; Morado & Small, 1995). Acineta and Tokophrya are two common genera that are found as free-living species or as facultative ectosymbionts, along with other suctorians , on copepods (Evans, Sell, & Beeton, 1981; Fernández-Leborans & Tato-Porto, 2000b; Grigorovich, Dovgal, MacIsaac, & Monchenko, 2001), isopods (Fernández-Leborans, Hanamura, & Nagasaki, 2002; Olafsdottir & Svavarsson, 2002), mysids (Fernàndez-Leborans & Tato-Porto, 2002), decapods (Fernàndez-Leborans & Gabilondo, 2006; Fernàndez-Leborans, Córdoba, & Gómez, 1997; Granados & Chinchilla, 1990; Vogelbein & Thune, 1988), and amphipods (Fernàndez- Leborans, Arndt, & Gabilondo, 2006; Walker & Roberts, 1982). The migratory swarmer , which is undescribed in many species, is the stage that infects new hosts or increases the colonization of the current host. Swarmers may be small and ciliated or large, worm-like and incapable of swim- ming. In the Laurentian Great Lakes , reinfestation of copepods by Tokophrya quadripartita occurs on a seasonal basis with peak prevalences of infesta- tion found in the summer months (Evans, Sicko- Goad, & Omair, 1979). Suctorians can be broadly distributed on the appendages of their crustacean hosts (e.g., Batisse, 1986; Fernàndez-Leborans & Tato-Porto, 2002; Nicol, 1984; Walker & Roberts) while others can show high site specificity (e.g., Batisse, 1973; Hitchen & Butler, 1972). The inten- sity of the suctorian infestation has been correlated to the age of the host: mature hosts can have almost ten times the number of suctorians as juvenile hosts (Fernàndez-Leborans & Tato-Porto, 2002). Several unusual suctorians even colonize the out- side of vertebrates, such as on the shell of turtles (Goodrich & Jahn, 1943) and the gills of Arctic char (Hofer, Salvenmoser, & Fried, 2005). At least two genera colonize the inside of vertebrates: Allantosoma is found in the cecum and colon of horses (Imai, 1979; Sundermann & Paulin, 1981); and Cyathodinium in the caecum of guinea pigs (Paulin & Corliss, 1964). Suctorians feed primarily on other ciliates , typi- cally showing little preference. However, haptorians and heterotrichs generally appear to be immune to suctorian predation (Batisse, 1994b). There is nevertheless some diversity in feeding habits. For example, Trematosoma may feed on bacteria (Batisse, 1973), Choanophrya feeds on particles of food debris derived from its copepod host (Hitchen & Butler, 1973a), and Phalacrocleptes feeds on the tissues of its polychaete host (Kozloff, 1966). Finally, there are some suctorians that are relatively small compared to their ciliate \u201cprey\u201d or host so that they have been described as parasites (Matthes, 1971). Podophrya species attach to the outside of their \u201chost\u201d ciliate, a Nassula species (Fauré-Fremiet, 1945) or Paramecium or Urostyla (Jankowski, 1963) or even become \u201cinternal\u201d pred- ators (Fig. 10.5). Pseudogemma species attacks the suctorian Acineta (Batisse, 1968). Podophrya may reach abundances sufficient to sometimes control Nassula populations (Canter, Heaney, & Lund, 1990). Pottsiocles invades its folliculinid heterotrich host (Chatton & Lwoff, 1927) while Endosphaera is found in the cytoplasm of trichodi- nid