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enabling the organism to continuously probe the environment for food while it moves forwards or backwards or remains stationary on it somatic cirri (Deitmer et al., 1984). The oral polykinetids and paroral of spirotrichs can be underlain by microtu- bules and/or a nodal filamentous reticulum , which may confer on the region a highly contractile nature (see references above). For example, tintinnids and other choreotrichs are able to not only contract the body but also the oral region, possibly due to these filamentous elements (Grim, 1987; Laval-Peuto, 1994). The microtubular elements likely provide structural support for the oral region (Grain, 1984; Tuffrau & Fleury, 1994). Large accumulations of pharyngeal disks in the oral region may enable spirotrichs, like Euplotes , to rapidly form as food vacuole membranes the rough equivalent of the entire surface area of the cell and so exploit a peri- odically abundant food source (Kloetzel, 1974). 7.5 Division and Morphogenesis Spirotrichs typically divide while free-swimming with few notable exceptions, such as the stichot- rich Paraholosticha (Dieckmann, 1988; Tuffrau & Fryd-Versavel, 1977). Foissner (1996b) presents a comprehensive review of the types of stomato- genesis and division morphogenesis in the ciliates. The literature on stomatogenesis of stichotrichs is particularly rich as the features of division morpho- genesis have been instrumental in establishing phy- logenetic hypotheses about relationships among families and genera (e.g., see Berger & Foissner, 1997; Eigner, 1997, 1999, 2001; Foissner, 1996b; Petz & Foissner, 1992). These, in turn, are now being tested by molecular phylogenetics (Bernhard et al., 2001; Foissner et al., 2004; Schmidt et al., 2007). Our review below will briefly characterize the nature of division morphogenesis in the vari- ous spirotrich subclasses. Because of Foissner\u2019s comprehensive review, few references are made to earlier literature. Stomatogenesis of the Subclass Protocruziidia (i.e., Protocruzia ) has been characterized as mix- okinetal since elements of both somatic and paren- tal infraciliature are involved in oral primordium formation (Foissner, 1996b). However, Grolière et al. (1980a) have provided the only published description, which does not demonstrate involve- ment of parental oral structures, typing it as parakinetal . The oral polykinetids assemble from anterior to posterior and from right to left in the primordial field while the paroral differentiates as a file of dikinetids along the right side of the primordial field (Fig. 7.7). Division morphogenesis has not been described for Phacodinium or Licnophora (Foissner, 1996b). This presents an opportunity for future research. Deroux (1974) provided the first detailed description of stomatogenesis in a choreotrich , Strobilidium . Foissner (1996b) classifies chore- otrich stomatogenesis as hypoapokinetal since it occurs for most of the process in a subsurface cortical pouch . Initial kinetosomal proliferation appears to occur on the cell surface, and the region invaginates as oral development proceeds (Dale & Lynn, 1998) (Fig. 7.8). The developing oral polyki- netids form a particularly characteristic \u201cbarrel stave-like\u201d formation across the outer or surface end of which the developing paroral extends (Fig. 7.8). Kinetosomal proliferation occurs within the somatic kineties, which lengthen and are sub- divided at cytokinesis . This has been observed in Strombidinopsis , Strobilidium , and tintinnids (Agatha, 2003a; Dale & Lynn, 1988; Deroux; Petz & Foissner, 1992, 1993). Hypotrichs also share the feature of oral pri- mordium development within a subsurface pouch , and have been characterized as hypoapokinetal (Foissner, 1996b) (Fig. 7.7). In hypotrichs , the earliest kinetosomes of the oral primordium appear in a subsurface pouch (e.g., Aspidisca , Song, 2003; Certesia , Wicklow, 1983; Diophrys , Hill, 1981; Song & Wilbert, 1994; Euplotes , Wise, 1965; Uronychia , Hill, 1990). However, the primordium develops on the cell surface of the related disco- cephalines (Wicklow, 1982). The somatic ciliature may be renewed differently on dorsal and ventral surfaces. On the ventral surface to the posterior right of the proter\u2019s oral region, typically five, but up to ten, primordial streaks form by kinetosomal replica- tion (Fig. 7.7). These kinetosomes appear not to be associated with parental somatic kinetids, but may acquire kinetosomes from parental structures as the parental structures dedifferentiate. These ventral streaks elongate and eventually split into two sets, one giving rise to the proter\u2019s and the other to the opisthe\u2019s ventral ciliature (e.g., Certesia , Wicklow, 1983; Diophrys , Hill, 1981; Song & Wilbert, 1994; Euplotes , Wise, 1965; Uronychia , Hill, 1990; dis- cocephalines , Wicklow, 1982). Movements of cirral primordia both posteriorly and anteriorly are driven by the assembly of microtubular structures associ- ated with them (Fleury, 1991a; Ruffolo, 1976b). Wallengren (1900) devised a method of numbering these ciliary streaks and the subsequently differen- tiating cirri in Euplotes and this has served as an important means of comparing the development of hypotrichs and stichotrichs (see also Martin, 1982; Wise, 1965). Dorsal kinety streaks may appear in both proter and opisthe alongside parental kineties, and with kinetosomal replication ultimately replac- ing the parental structures (e.g., Diophrys , Song & Wilbert, 1994). In contrast, dorsal kinetosomal replication in euplotids occurs within each dorsal kinety (Frankel, 1975; Song, 2003). The pattern of intensity of replication is guided by global posi- tional systems (Frankel, 1989). Oligotrich stomatogenesis appears to fall into two types, possibly related to the extent of develop- ment of the cortical polysaccharide plates. Foissner (1996b) typed it as epiapokinetal because the oral primordium forms on the cell surface independ- ent of parental infraciliature in some Strombidium species (Agatha, 2003b; Agatha, Strüder-Kypke, & Beran, 2004; Song & Wang, 1996). However, Fauré-Fremiet (1953) described it to occur in a long inpocketing beneath the polysaccharide plates of Strombidium oculatum , and this neoformation organelle was confirmed in Pelagostrombidium fallax by Petz and Foissner (1992). In the early stages of oral primordium formation, prolifera- tion may begin on the cell surface, followed by invagination as development of the oral structures proceeds (Petz, 1994) (Fig. 7.8). This is similar to the process in the choreotrichs , and later dividers in both groups may be characterized as showing an enantiotropic kind of cell division (Fauré-Fremiet, 1953; Petz & Foissner, 1993). There is a rich literature on the patterns of division morphogenesis in stichotrichs with the perspectives of different investigators leading to very different sets of relationships (e.g., see Berger & Foissner, 1997; Eigner, 1997, 1999; Martin, 1982; Wicklow, 1981). The pattern of development has been inter- preted using the system of Wallengren (1900), which has been modified to accommodate a larger diversity of patterns (e.g., Martin, 1982). Pattern development in ciliates is controlled at both global and local levels, and although we have some ideas of the properties of the developmental processes, 7.5 Division and Morphogenesis 163 Fig. 7.7. Division morphogenesis of representatives from each of the subclasses of the Class SPIROTRICHEA . A Subclass Protocruziidia . In Protocruzia , stomatogenesis appears to be parakinetal here, involving kinetosomal pro- liferation adjacent to the equatorial region of Kinety 1 ( a , b ) and then differentiation of the adoral polykinetids and paroral ( c-e ) (from Grolière et al., 1980a). However,