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, a remnant of the c segment, retained as a kinetosomal grouping that lies in the director meridian , the postoral space between kinety 1 and kinety n (Coats & Small, 1976). During phi- lasterine stomatogenesis , kinetosomal proliferation occurs in relation to each of these components, pro- viding kinetosomes for the opisthe oral structures, while the parental structures reorganize to form the proter oral apparatus (Fig. 15.10). This pattern has been observed in Cohnilembus (Didier & Detcheva, 1974), Dexiotricha (Peck, 1974), Philaster (Coats & Small), Potomacus (Ramsey, Brownlee, & Small, 1980), Mesanophrys (Morado & Small, 1994), Uronemella (formerly Uronema filificum ) (Ma, Song, & Ma, 2002; Pérez-Uz, Song, & Warren, 1996), Paranophrys (Ma, Song, & Hu, 2001), Metanophrys (Ma & Song, 2003), Pseudocohnilembus (Ma et al., 2003b), and Uronema (Ma et al., 2004). There is a considerable diversity in oral structure morphology and patterns of stomatogenesis within the estab- lished families of philasterines , and this is confirmed by diversity in the SSUrRNA gene sequences (Lynn & Strüder-Kypke, 2005; Ma et al.). This calls into question the taxonomy of the scuticociliates pre- sented by Lynn and Small (2002). We have, how- ever, basically retained these familial assignments 15.5 Division and Morphogenesis 317 318 15. Subphylum 2. INTRAMACRONUCLEATA: Class 9. OLIGOHYMENOPHOREA until a clearly rationalized alternative arrangement is proposed ( see Chapter 17 ). There have been only a handful of recent studies on pleuronematine and thigmotrich scuticociliates using protargol silver impregnation, the staining procedure that best reveals kinetosomal structures. Thus, generalizations for these groups cannot easily be made. Dolan and Antipa (1985) suggested two stomatogenetic patterns for these non- philasterine scuticociliates : (1) oral primordia derived from the paroral and scuticovestige , observed in Ancistrum (Hatzidimitriou & Berger, 1977), Cyclidium (Grolière, 1980), and Conchophthirus (Antipa & Hatzidimitriou, 1981); and (2) oral primordia derived only from the paroral , accompanied by considerable dedifferentiation of the parental oral apparatus, observed in Histiobalantium (Dragesco & Iftode, 1972), Mytilophilus and Peniculistoma (Dolan & Antipa), and Pleuronema (Grolière & Detcheva, 1974; Ma, Gong, & Song, 2003a; Small, 1967) (Fig. 15.11). Njiné and Ngassam (1993) have shown that stomatogenesis in the thigmo- trich hysterocinetid Ptychostomum begins as a parakinetal kinetosomal proliferation , anterior to the parental oral apparatus. While this distances the hysterocinetids from other thigmotrichs , we do not believe it yet warrants placing them in a sepa- rate subclass, as suggested by some (de Puytorac, 1994f; Ngassam & Grain, 2002). It is important to remember that position is developmentally \u201cprior\u201d to pattern. Thus, we conclude that hysterocinetid stomatogenesis may be one of those instances where our interpretation of the underlying morpho- genetic \u201cpattern\u201d is confused by the surface kineto- somal structures. We await molecular evidence to refute or corroborate their position as thigmotrichs within the Subclass Scuticociliatia . The hymenostomes have been reduced to a smaller subset of oligohymenophorean families, which Foissner (1996b) categorizes as showing parakinetal stomatogenesis . Tetrahymena is the archetypical hymenostome , showing monoparaki- netal stomatogenesis (Fig. 15.11) (Frankel, 1989; Grolière, 1975a). The oral primordium typically forms at the equator by kinetosomal prolifera- tion at what is defined as Kinety 1, the \u201cstoma- togenic kinety\u201d , but which is reported to occur at other kineties also (Frankel, 1966, 1989; Nanney, 1967). This typical hymenostome pattern has been observed in Glaucoma (Frankel, 1960; Peck, 1975), Tetrahymena (Bakowska, Nelsen, & Frankel, 1982a; Grolière), and Turaniella (Iftode et al., 1970). The polykinetids assemble through a proc- ess reminiscent of that described in the spirotrichs by Jerka-Dziadosz (1981a). Dikinetids are formed that later align to form the two primary rows of each oral polykinetid, followed by replication of a third and sometimes fourth row (Bakowska et al., 1982b; Frankel et al., 1984a, 1984b). The gradient of differentiation proceeds from the upper left of the primordial field to the lower right (Peck, 1974). The paroral finally develops along the right border of the primordial field by assembly of a ciliated file of single kinetosomes that replicate an external kinetosome to form the paroral dikinetids . These external kinetosomes become ciliated as the inter- nal kinetosomes lose their cilia (Bakowska et al., 1982a, 1982b; Nelsen, 1981). What is intriguing is the pattern of paroral assembly and disassembly in the proter: the external kinetosomal file separates from the internal and a new external kinetosome is replicated prior to the dedifferentiation of the \u201cold\u201d kinetosomes (Bakowska et al., 1982a, 1982b; Nelsen, 1981). Bakowska et al. (1982b) make the intriguing proposal that this is a phylogenetic signal of the common ancestry of hymenostomes and scuticociliates , and by extension even to the peniculines \u2013 in the hymenostomes , these \u201cold\u201d kinetosomes normally dedifferentiate rather than remain to participate in the next fission. This archetypical hymenostome pattern is mod- ified in two circumstances. First, during oral replacement , the oral apparatus is dedifferentiated and replaced without cell division in microstome hymenostomes when proliferation of kinetosomes from the \u201cold\u201d paroral and a region posterior to the parental oral apparatus provides the source of kinetosomes for the new oral apparatus (Frankel, 1989; Williams & Frankel, 1973). This pattern of stomatogenesis is also characteristic of those Tetrahymena species that transform into macros- tomes , developing the larger oral apparatus by a process of replacement similar to that in the microstomatous species described above (Buhse, 1966; Méténier & Grolière, 1979; Njiné, 1972). The second modification of this pattern occurs in the ophryoglenines whose pattern is characterized as teloparakinetal (Foissner, 1996b). In this group, adapted for histophagy and parasitism, cell division of the encysted tomont is preceded by complete dedifferentiation of the parental oral structures. Only at the end of the series of palintomic divi- sions does the oral apparatus differentiate from an oral primordium derived by replication at the anterior ends of a number of somatic kineties. The paroral in Ophryoglena and Ichthyophthirius is completely dedifferentiated during the final stages of stomatogenesis, a feature these ophryoglenines share along with the differentiation of the organelle of Lieberkühn (Foissner, 1996b; de Puytorac et al., 1983b). Division morphogenesis of peritrichs can be relatively simple in solitary forms, and can become increasingly more complex in colonial forms and in symbiotic forms. In colonial forms, such as Zoothamnium species, cell division and subse- quent development can explain the structure of the colony itself and the differentiation of several types of zooids (Fauré-Fremiet, 1930; Summers, 1938). In symbiotic epibionts, division and forma- tion of telotrochs appear to be correlated with the molt cycle of their crustacean hosts (Clamp, 1973; Walker, Roberts, & Usher, 1986). Lom (1964) provided the modern schema for peritrich stoma- togenesis by studying protargol impregnations of dividing Telotrochidium . A germinal kinety or field , adjacent to the parental paroral , proliferates to provide kinetosomes for the opisthe\u2019s paro- ral and oral polykinetids 2 and 3 (Fig. 2\u20136Ac). The parental paroral provides kinetosomes for the opisthe\u2019s oral polykinetid