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Foissner (1996b) has evidence that it is mixokinetal , involving elements from the parental oral region. B Subclass Hypotrichia . In Diophrys , the oral primordium begins develop- ment in a subsurface pouch while five ventral streaks appear at the cell equator ( a ). The ventral streaks divide into an anterior or proter and posterior or opisthe group ( b , c ). Cirral differentiation and migration occur as the oral cili- ature develops ( c , d ). (from Hill, 1981.) C Subclass Stichotrichia . In Parakahliella , the oral primordium develops by kinetosomal proliferation on the ventral surface ( a , b ). Two sets of ventral streaks - an anterior proter set and a posterior opisthe set develop and cirri differentiate and migrate as the oral primordium continues to develop ( c , d ). (from Berger et al., 1985.) Fig. 7.8. Division morphogenesis of representatives from each of the subclasses of the Class SPIROTRICHEA . A Subclass Stichotrichia . In Halteria , formerly an oligotrich , the oral primordium (arrowhead) develops on the cell surface ( a ). New sets of bristle kinetosomes appear anterior and posterior (arrows) to parental bristle kinetosomes , which eventually dedifferentiate as development proceeds ( b\u2013d ). (from Song, 1993.) B Subclass Choreotrichia . In Strombidinopsis , the oral primordium begins development in a subsurface pouch (arrow) ( a ). Oral development pro- ceeds to a \u201cbarrel stave-like\u201d formation ( b, c ), and then the opisthe\u2019s oral structures expand out onto the cell surface (d ). Kinetosomal replication of somatic kinetids occurs within the kineties. (from Dale & Lynn, 1998.) C Subclass Oligotrichia . In Strombidium , the oral primordium (arrow) begins development on the cell surface in the region of junction between the ventral kinety and the girdle kinety ( a ). As development of the oral primordium proceeds, there is kinetosomal replication in the girdle and ventral kineties and a complex series of morphogenetic movements ( b, c ). (from Petz, 1994.) 7.5 Division and Morphogenesis 165 166 7. Subphylum 2. INTRAMACRONUCLEATA: Class 1. SPIROTRICHEA the actual cellular mechanisms remain to be deter- mined (Frankel, 1989). Martin (1982), for exam- ple, assumes homology between hypotrichs and stichotrichs using a Wallengren -like numbering system. We believe it premature to assume that these patterns are homologous until we have a firmer understanding of the underlying cellular mecha- nisms determining pattern development. Thus, we present only a general description of stichotrich division morphogenesis , touching on some major differences in the development of pattern (Fig. 7.7). It may be that the application of molecular approaches will not only provide refutation of competing schemes derived by morphologists, but application of molecular phylogenetics may inform the evolution of division morphogenesis in stichot- richs. A general assumption is made that the ances- tral stichotrich was a ciliate with many files of small cirri (e.g., Phacodinium , Fig. 7.2; Plagiotoma , Fig. 7.4), and that as evolution proceeded this number was reduced to a few scattered cirri (e.g., Stylonychia , Fig. 7.4), although it now seems that Plagiotoma is a derived form (Foissner et al., 2004; Schmidt et al., 2007). Foissner (1996b) tentatively characterizes stomatogenesis in Plagiotoma as par- akinetal. Somatic kineties are completely renewed during division morphogenesis by proliferation of streaks within the parental kineties in both the proter and opisthe (Albaret, 1973; Fleury, 1983). These features, along with macronuclear repli- cation bands (Dworakowska, 1966), support its placement within the Subclass Stichotrichia . Among stichotrichs , there is a bewildering array of patterns, placed into parakinetal and epiapoki- netal types by Foissner (1996b), who admits that all stichotrichs may be epiapokinetal since electron microscopy does not clearly implicate parental structures in kinetosomal replication (Grimes, 1972, 1973). Whether or not the oral primordium proliferates in relation to the parental infracili- ature, the ventral cirral primordia may arise in at least two ways in the opisthe. The proter ventral cirral primordia almost always arise separately from those of the opisthe, so two sets of somatic cirral streak primordia are present in stichotrichs at the outset, rather than one set that divides as in the hypotrichs (Fig. 7.7). To simplify the diversity of patterns considerably, in the vast majority of genera, a series of streaks , from 3 to more than 20, arise separately from the oral primoridium often in association with the dedifferentiation of parental cirri (Fig. 7.7) (e.g., Amphisiellides , Eigner & Foissner, 1994; Bakuella , Eigner & Foissner, 1992; Coniculostomum , Kamra & Sapra, 1990; Deviata , Eigner, 1995; Gastrostyla , Hu & Song, 2000; Hemigastrostyla , Song & Hu, 1999; Holosticha , Hu & Song, 2001a; Histriculus , Berger, Foissner, & Adam, 1985; Kahliella , Berger & Foissner, 1988; Lamtostyla , Petz & Foissner, 1996; Laurentiella , Martin, Fedriani, & Perez-Silva, 1983; Parakahliella , Berger & Foissner, 1989b; Paraurostyla , Wirnsberger, Foissner, & Adam, 1985; Steinia , Voss & Foissner, 1996; Stylonychia (= Tetmemena ), Wirnsberger, Foissner, & Adam, 1986; Thigmokeronopsis , Hu, Song, & Warren, 2004; Wicklow, 1981; Urosomoida , Ganner, Foissner, & Adam, 1986/1987). The other way is for a series of streaks , from five to more than ten, to appear to derive from the opisthe oral primor- dium (e.g., Amphisiella , Voss, 1992; Circinella , Foissner, 1994a; Gonostomum , Song, 1990a; Metaurostylopsis , Song, Petz, & Warren, 2001; Pseudokeronopsis , Hu & Song, 2001b; Urosoma , Foissner, 1983a). In both cases, the relation of cir- ral structures to the oral primordium may be more a function of the density of ciliation on the ventral surface. Where cirri are dense, cirral primordia appear to arise separately from the oral primor- dium; and where cirri are sparse, cirral primordia appear to emerge by kinetosomal proliferation from the oral primordium. Until we have more concrete understanding of the mechanisms under- lying primordium formation, we should not put too much weight on subtle differences in these spatial patterns. Primordia for marginal cirri and for dorsal kine- ties typically develop within the parental files and as proliferation proceeds, the parental kinetosomes are resorbed. However, the primordia may also appear beside the parental files and subsequent migration may make it appear that proliferation has occurred within the parental cirral file (see Wirnsberger et al., 1985). Finally, Eigner (1995, 1997, 2001) has defined neokinetal proliferation , especially in forms with longitudinal cirral files, in which additional new primordia or anlagen derive from the primary anlagen and migrate anteriorly or posteriorly from it to provide new structures. Two unusual groups bear special mention. First, Paraholosticha divides within a cyst , dedifferen- tiating all parental structures first and then devel- oping new structures in an epiapokinetal fashion (Dieckmann, 1988). Foissner (1996b) speculated that this may have evolved as an adaptation to the highly variable terrestrial and semiterrestrial habi- tats in which Paraholosticha is found, demonstrat- ing a parallel evolution with division morphogenesis in some colpodeans (see Chapter 12 ). Second, the halteriids , such as Halteria and Meseres , are now placed by molecular sequences within the Subclass Stichotrichia (Bernhard et al., 2001), so the plank- tonic \u201c oligotrich \u201d body form has evolved conver- gently in stichotrichs . Stomatogenesis in halteriids is typed as epiapokinetal like that of other stichot- richs (Foissner, 1996b). The somatic infraciliature is replaced