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& Walkosz, 1975). The transformation of the telotroch to a stalked zooid has been studied in the colonial Zoothamnium and solitary Vorticella , under controlled culture conditions (Suchard & Goode, 1982; Vacchiano et al., 1992). Stalk forma- tion requires microtubules to transport secretory vesicles to the sites of exocytosis as the stalk forms and elongates (Suchard & Goode, 1982). Fig. 15.6. Schematics of the somatic kinetids of the Class OLIGOHYMENOPHOREA . ( a\u2013d ) Kinetids of the Subclass Peniculia . ( a\u2013c ) Dikinetids of the Order Peniculida \u2013 Paramecium ( a ), Disematostoma ( b ), Frontonia ( c ). (d ) Monokinetid of the Subclass Peniculia and Order Urocentrida \u2013 Urocentrum . ( e , f ) Monokinetids of the Subclass Apostomatia \u2013 Hyalophysa ( e ) and Collinia ( f ) (from Lynn, 1981, 1991) The stalk of sessiline peritrichs is composed of the secreted outer sheath that surrounds, in some species, an extension of the zooid \u2019s cytoplasm. The bulk of this extension is filled with a contractile myoneme , called the spasmoneme (Allen, 1973a, 1973b). The spasmoneme is continuous with the filamentous myonemes in the zooid itself, and these, in turn, are attached by a linkage complex to adjacent cisternae of endoplasmic reticulum, which may be the sites for Ca 2+ necessary to induce contraction (Allen, 1973a, 1973b). The contractile proteins of the spasmoneme are not related to actin or myosin , and have therefore been termed spas- mins (Amos, Routledge, & Yew, 1975; Routledge, 1978). Spasmins , which are related to centrin and calmodulin , may not be solely responsible for contraction (Asai, Ninomiya, Kono, & Moriyama, 1998). In addition to these filamentous myonemes of the zooid , there are other contractile filaments that retract the epistomial disk and there is a collar sphincter that closes the apical pole (Lom, 1994). The other major group of peritrichs , the mobilines , are distinguished by an aboral adhesive disk (Fig. 15.3). On its oral side, the adhesive disk is bounded by a locomotor fringe , organized in three compo- nents in trichodinids: an \u201coral\u201d or superior girdle of solitary or paired lateral cilia; a locomotor wreath or middle girdle, composed of oblique rows of 3\u20138 kinetosomes, reminiscent of the telotroch girdle of Opisthonecta ; and an \u201caboral\u201d or inferior girdle of groups, typically pairs of kinetosomes and cilia (Hausmann & Hausmann, 1981a; Maslin-Leny & Bohatier, 1984). Fibrillar rootlets attach the kine- tosomes of the inferior and middle girdles respec- tively to the outer peripheral pin and middle radial pin of the skeletal components of the adhesive disk (Hausmann & Hausmann, 1981b). The radial pins articulate with the innermost skeletal element, the Fig. 15.7. Schematics of the somatic kinetids of the Class OLIGOHYMENOPHOREA . ( a\u2013e ) Kinetids of the Subclass Hymenostomatia \u2013 Monokinetids of Tetrahymena ( a ), Glaucoma ( b ), Colpidium ( d ), and Ichthyophthirius (e ). Dikinetid of Colpidium ( c ). ( f ) Monokinetid of the Subclass Astomatia \u2013 Coelophrya (from Lynn, 1981, 1991) 15.3 Somatic Structures 305 306 15. Subphylum 2. INTRAMACRONUCLEATA: Class 9. OLIGOHYMENOPHOREA denticles , which have been traditionally used after silver staining , to discriminate genera and species. The denticles have a complex structure whose detailed anatomy has only recently been revealed by scanning electron microscopy preceded by either nitric acid dilution (Kruger, Basson, & Van As, 1993) or sonication (Gaze & Wootten, 1999). To further complicate the interpretation of these denticles in a taxonomic context, their relative morphology can change as the diameter of the mobiline body increases (Kazubski, 1967). Given these insights, molecular genetic studies are now required to test the robustness of a taxonomy that is based primarily on denticle morphology. Oligohymenophoreans are rarely found within loricas or other secreted structures. Among the free-living forms, the scuticociliate Calyptotricha is an exception, building a tube-like lorica in which it lives (Wilbert & Foissner, 1980). However, the peritrichs include several families characterized by the form and diversity of their loricas , which can have a smooth or more architectured surface (e.g., Couch, 1973; Clamp, 1987, 1990, 1991, 1992; Finley & Bacon, 1965; Warren & Carey, 1983). The lorica is a structure, primarily proteinaceous, which is likely secreted by the scopula in some species (González, 1979). The lorica of Platycola apparently sequesters heavy metals , such as manga- nese , preferentially concentrating them above their environmental concentrations (Warren & Carey, 1983). Undoubtedly the most conspicuous secreted structure among peritrichs , and perhaps ciliates as a phylum, is the gelatinous matrix secreted by Ophrydium species, which can range from 2 cm in diameter up to 30 cm in diameter (Duval & Margulis, 1995; Winkler & Corliss, 1965). Fig. 15.8. Schematics of the somatic kinetids of the Subclass Scuticociliatia of the Class OLIGOHYMENOPHOREA . (a , b ) Monokinetid and dikinetid of Cinetochilum . ( c ) Monokinetid of Dexiotricha . ( d , e ) Monokinetid and dikinetid of Cohnilembus . ( f ) Monokinetid of Conchophthirus (from Lynn, 1981, 1991) Fig. 15.9. A Schematics of the somatic polykinetid of the scuticociliate Schizocaryum of the Class OLIGOHYMENOPHOREA (from Lynn, 1981, 1991). B Somatic cortex of a typical oligohymenophorean based on the somatic cortex of Tetrahymena and Colpidium 15.3 Somatic Structures 307 308 15. Subphylum 2. INTRAMACRONUCLEATA: Class 9. OLIGOHYMENOPHOREA Contractile vacuoles are a conspicuous organelle in many oligohymenophoreans . They are typically solitary and restricted to the posterior half of the cell. However, peniculines often have two, one in each half of the cell while astomes can have doz- ens, whose distribution patterns have been used to characterize species (de Puytorac, 1994g). The con- tractile vacuole of peritrichs is cryptic as it opens into the infundibulum at the anterior end of the cell. New contractile vacuoles are positioned at each cell division by a global positioning system that is able to proportionally \u201cmeasure\u201d cell size (Frankel, 1989; Nanney, 1980; Nanney, Nyberg, Chen, & Meyer, 1980b). The contractile vacuole complex of oligohymenophoreans , such as Paramecium , Tetrahymena , and Vorticella , is composed of two major membranous compartments, the spongiome and the contractile vacuole itself (Patterson, 1980; Allen & Naitoh, 2002). Much remains to be learned of the details of the mechanism of water sequestra- tion . It is clear that the spongiome membrane has vacuolar-ATPases that pump ions, probably K + and Cl\u2212 , into this compartment to create an osmotic gradient drawing water and metabolic wastes from the cytosol (Allen & Naitoh; Allen, Ueno, Pollard, & Fok, 1990; Stock, Gronlien, Allen, & Naitoh, 2002). Fluid is then moved to the contractile vacuole itself, which periodically rounds prior to expulsion. The fluid is excreted through the con- tractile vacuole pore , which is supported by heli- cally coiled microtubules, and which serves as the origin for ribbons of microtubules that radiate out from the pore to support the membranous compo- nents of the spongiome (Chapman & Kern, 1983; McKanna, 1973a). Similar to natural populations of marine ciliates, Paramecium species continue to adapt and maintain contractile vacuole function, even in environments with high osmotic strength. They do this, in part, by regulating the amounts of the free amino acids proline and alanine in the cytoplasm (Cronkite & Pierce, 1989). Stock, Allen, and Naitoh (2001) argued that the maintenance of contractile vacuole function, even at these high