the “exconjugants” (Kaczanowski, Radzikowski, Malejczyk, & Polakowski, 1980). Nevertheless, interaction of cells requires participation of the sur- face glycocalyx as in other ciliates (Golembiewska & Radzikowski, 1980). Kaczanowski et al. (1980) speculated that the adaptive advantage of intrac- lonal conjugation or inbreeding to Chilodonella steini is that it is a rare ciliate and has a special feeding preference for living diatoms. Inbreeding species generally are adapted to narrow ecological niches (Nyberg, 1974). The genetics of mating types in suctorians has been most thoroughly investigated in only one series of studies. Colgin-Bukovsan (1976) demon- strated that Tokoprhya lemnarum has two mating types , one being homozygous and the other hetero- zygous or hemizygous. Mating occurs between cells of complementary mating type . Although it occurs under all nutritive conditions, cells that are slightly starved showed peak reactivity (Colgin-Bukovsan, 1979). This suctorian shows a typical clonal life cycle with immaturity, maturity, and senescence stages. The long periods of immaturity and maturity (i.e., at least 800 fissions) characterize this species as a typical outbreeder (Colgin-Bukovsan, 1979). The life span of individual Tokophrya is quite vari- able, ranging from several days to over 1 month. However, individual lifespans are dramatically reduced as clones become senescent (Karakashian et al., 1984). Senescence is also accompanied by morphological abnormalities arising from incom- plete budding (Batisse, 1994b). With so few stud- ies, clearly much remains to be learned about sexual reproduction in this class. 10.7 Other Features Cyrtophorians , especially chilodonellids , are con- spicuous species in the biofilms in wastewater treatment facilities . Their presence has been used to assess efficiency of operation of these facilities where these ciliates were indicative of good water purification conditions, both within plants (Martin- Cereceda, Serrano, & Guinea, 2001a) and in the natural environment (Bick, 1972; Foissner, 1988a). They do show high sensitivities to heavy metals , such as cadmium and copper , and this may negatively impact their role in treatment facilities (Madoni, Davoli, Gorbi, & Vescovi, 1995). However, this high sensitivity to copper has been exploited to our advantage as a preventative measure to reduce their incidence as fish ectoparasites in aquaculture facil- ities (Horwath, Lang, & Tamas, 1978). Treatments with dilute sodium chloride and malachite green and formalin can also be effective (Hoffman, 1978; Lom, 1995; Rowland, Mifsud, Nixon, & Boyd, 2006). Finally, Henebry and Ridgeway (1979) sug- gested that the high prevalence of ectosymbiotic Tokophrya on planktonic microcrustaceans might be used as an indicator of eutrophic water conditions. 10.7 Other Features 231