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the cytostomal region of Dileptus where kinetosomes are supplied to the enlarging circumoral kinety and to adjacent elongating somatic kineties. In contrast, Goli\u144ska (1984) examined the effects of reduced cell size on ultrastructural components of the cell: Dileptus reduced in size by microsurgery had oral nema- todesmata and transverse ribbons that contained fewer microtubules. However, the reduction was not perfectly proportional to the reduction in cell size , suggesting that some lower limit may exist for a functional organelle (Goli\u144ska, 1984). In con- trast, in overfed Dileptus , although the number of oral nematodesmata might increase, the number of microtubules in these nematodesmata and in trans- verse ribbons did not vary, suggesting an upper size-limit on these structures (Goli\u144ska, 1986). High temperatures can cause abnormalities in the oral development, probably by interfering with microtubule assembly (Goli\u144ska, 1988). 9.5 Division and Morphogenesis Litostomes typically divide while swimming freely, although some pleurostomatids may divide within a cyst . Stomatogenesis is telokinetal and the parental oral structures are retained. Foissner (1996b) distinguished four subtypes in the class, primarily characterizing different ordinal or sub- ordinal assemblages. The majority of taxa within the Subclass Haptoria are characterized as under- going holotelokinetal stomatogenesis , with the \u201canterior\u201d ends of all the opisthe somatic kineties undergoing kinetosomal differentiation and pro- liferation to produce the oral dikinetids (Fig. 9.6) (e.g., Fuscheria , Spathidium \u2013 Berger, Foissner, & Adam, 1983; Homalozoon \u2013 Leipe, Oppelt, Hausmann, & Foissner, 1992). Dileptus has also been characterized as holotelokinetal . However, the development of the proboscis and its ciliary fields means that kinetosomal proliferation at the equa- tor gives rise to both the proboscis infraciliature and the circumoral dikinetids (Goli\u144ska, 1995). Pleurostomatid stomatogenesis is characterized as monotelokinetal as only the somatic portions of the oral kineties are involved (e.g., Litonotus , Loxophyllum \u2013 Fryd-Versavel, Iftode, & Dragesco, 1976). The endocommensal vestibuliferids are characterized as undergoing intertelokinetal stoma- togenesis (Foissner, 1996b). Kinetosomal prolifera- tion occurs at the ends and by elineation or laterally to produce kinetofragments between the anterior ends of the somatic kineties (e.g., Balantidium \u2013 Fauré-Fremiet, 1955; isotrichids , paraisotrichids , and buetschliids \u2013 Grain, 1966a). The buetschliid Polymorphella may be the only exception as it appears to have holotelokinetal stomatogenesis (Foissner 1996b; Grain 1966a). It might be more appropriate to classify the stomatogenesis of buet- schliids as cryptotelokinetal (see below) since the region of oral kinetosomal proliferation usually has non-ciliated somatic kinetosomes. The entodiniomorphids have long been con- sidered to have apokinetal stomatogenesis since somatic kinetosomes were not visible by light microscopy. Furness and Butler (1986) have demon- strated that proliferation of oral kinetosomes occurs from non-ciliated somatic kinetosomes distributed in the cortex of Eudiplodinium . A similar process may explain the appearance of the new girdles in the haptorian Didinium as they appear \u201cde novo\u201d at some distance from the parental girdles (Small, Antipa, & Marsza\u142ek, 1972). This is presumably the case for all entodiniomorphids (Fernández-Galiano, Serrano, & Fernández-Galiano, 1985; Ito & Imai, 2005; Ito, Miyazaki, & Imai, 2001) and blepharo- corythids (Wolska, 1966), and has lead to describing the process as cryptotelokinetal (Foissner, 1996b). Several primordial fields may develop, typically in cortical pockets , and then later fuse to form the diff erentiated oral structures (Fig. 9.6). Cameron and O\u2019Donoghue (2001) have concluded that the stomatogenesis of Macropodinium , the genus endosymbiotic in kangaroos and wallabies , is very unusual, having features of epiapokinetal , endoapokinetal , and cryptotelokinetal stomatogen- esis depending upon the infraciliary structures involved. Clearly, an ultrastructural study is needed to resolve these questions. Moreover, stomatogen- esis has not been studied in representatives from all 9.5 Division and Morphogenesis 205 206 9. Subphylum 2. INTRAMACRONUCLEATA: Class 3. LITOSTOMATEA the families in this class, so there is clearly much comparative work to do. There is an extensive literature on the morpho- genesis and cell biology of regeneration in litostomes, particularly using the genera Dileptus and Lacrymaria (Frankel, 1989). Both ciliates can be sectioned by microsurgery and regeneration follows. If the proboscis or trunk of Dileptus is isolated, each part can proportionally regulate a smaller \u201cbody\u201d over several days (Goli\u144ska, 1979; Goli\u144ska & Kink, 1977). Regeneration involves the proliferation of new kinetosomes in both genera (Bohatier, 1972; Goli\u144ska; Kink, 1972). Initially regeneration stomatogenesis apparently requires neither RNA nor protein synthesis. However, \u201csta- bilization\u201d of the oral structures and development of toxicysts does require these two crucial cell processes (Bohatier & Kink, 1977; Goli\u144ska & Bohatier, 1975). A fuller discussion of this research can be found in Frankel (1989). 9.6 Nuclei, Sexuality and Life Cycle Litostomes are typical ciliates, having at least one macronucleus and one micronucleus . Macronuclear DNA does not appear to be fragmented into gene- Fig. 9.6. Division morphogenesis of litostomes . A In the haptorian Spathidium , its holotelokinetal stomatogenesis begins with proliferation of circumoral dikinetids at the equator of all somatic kineties ( a , b ). These kinetofragments bend rightward to extend across the interkinetal space and so form the opisthe\u2019s circumoral dikinetid as division morphogenesis is completed ( c , d ) (from Berger et al., 1983). B In the entodiniomorphid Entodinium , what appears to be apokinetal is now considered cryptotelokinetal because there are somatic kinetosomes scattered throughout the cortex. Kinetosomes first appear on the right ventral side ( a ) and as these proliferate to form a polybrachykinety another field forms on the dorsal left side ( b ). These two primordia meet as replication continues ( c ). Ultimately, a portion invaginates to become the infundibular or vestibular portion ( d , e ) (from Fernández-Galiano et al., 1985.) sized pieces (e.g., Didinium \u2013 Riley & Katz, 2001). Macronuclear shapes can be quite variable, ranging from small ovoid to very elongate and band-shaped (e.g., Didinium ). Pleurostomatids often have the macronucleus in pairs or quartets. Some vestibulif- erids (e.g., Isotricha ) have filaments extending from the ecto-endoplasmic layer to form a karyophore (Grain, 1966a). The macronucleus and micro- nucleus are typically quite closely associated in trichostomes with the micronucleus often residing in a depression in the macronucleus (Grain, 1994). Although appearing multiple, the macronucleus may in fact be moniliform, like a string of beads, with the number of beads increasing as cell size increases (Leipe & Hausmann, 1992). These beads condense prior to macronuclear division , while the more elongate and band-shaped macronuclei become ovoid. Macronuclear and micronuclear division are accomplished by intranuclear micro- tubules (e.g., Isotricha \u2013 Grain, 1966a; Didinium \u2013 Karadzhan & Raikov, 1977; Homalozoon \u2013 Leipe & Hausmann). Relatively little research has been done on con- jugation processes in litostomes , and the event is rarely observed in natural populations (Lucchesi & Santangelo, 2004). What we know derives mostly