Pré-visualização17 páginas
1984; Grim, 1982; Tuffrau & Fleury, 1994). Some oligotrichs , such as Strombidium , have numerous polygonal, cortical platelets of polysac- charide , which typically underlie the cortex in the posterior portion of the body. Coloration can be quite variable in spirotrichs , due to the presence of pigment granules , sequestered prey chloroplasts (see Life History ), and Chlorella symbionts. The color and nature of the granules can be important features to distinguish species (e.g., Berger & Foissner, 1987, 1989a). Since the somatic kinetids of the different sub- classes appear to be quite different, we will deal briefly with a characterization of the somatic kinetids of each subclass, treating the stichotrichs and hypotrichs together for comparative purposes. Protocruzia is the only genus in the Subclass Protocruziidia (Fig. 7.2). Grolière et al. (1980a) described its kinetids, which may be characterized as follows: a ciliated anterior kinetosome bearing a tangential transverse ribbon at triplets 4 and 5; a ciliated posterior kinetosome bearing a smaller transverse ribbon of 1\u20132 microtubules near triplet 4, a set of 10\u201315 divergent posticiliary microtubules that extend posteriorly to slightly overlap adjacent sets, and a striated kinetodesmal fibril at triplets 5 and 6 that extends to the right and anterior but does not overlap the fibril of the next anterior kinetid (Fig. 7.5). Although the postciliary ribbons are large, they do not form postciliodesmata as typical of the Class HETEROTRICHEA (see Chapter 6 ). Phacodinium is the only genus in the Subclass Phacodiniidia (Fig. 7.2). It is characterized as hav- ing linear somatic polykinetids composed of up to nine linked ciliated kinetosomes. There is dor- soventral differentiation of these polykinetids: on the dorsal surface, there are 1\u20133 kinetosomes with only one cilium; and, on the ventral surface, there are 9\u201311 ciliated kinetosomes (Fernández-Galiano & Calvo, 1992). Each kinetosome has the classi- cal fibrillar associates: a very slightly convergent postciliary ribbon that extends posteriad; a short, tapering, laterally-directed kinetodesmal fibril that arises near triplets 5\u20137, and a tangentially-oriented transverse ribbon that extends a short distance laterally into the adjacent ridge from triplets 3 and 4 (Fig. 7.5) (Didier & Dragesco, 1979). There are some polykinetids with \u201ctwo\u201d files of kinetosomes. These \u201chomologues of cirri\u201d are seemingly organ- ized in a zig-zag pattern with each kinetosome retaining all its fibrillar associates (Da Silva Neto, 1993a). Fig. 7.5. Schematics of the somatic kinetids of representatives of the Class SPIROTRICHEA . ( a ) Dikinetid of Protocruzia . ( b ) Linear polykinetid of Phacodinium . ( c ) Dorsal dikinetid of Euplotes . ( d ) Somatic dikinetid of Transitella . ( e ) Dorsal dikinetid of Stylonychia . ( f ) Ventral dikinetid of Engelmanniella . (from Lynn, 1981, 1991.) 7.3 Somatic Structures 157 158 7. Subphylum 2. INTRAMACRONUCLEATA: Class 1. SPIROTRICHEA Licnophora is one of two genera in the Subclass Licnophoria (Fig. 7.2). Its hourglass shape has the adoral zone at the \u2018anterior\u2019 and several rings of cilia surrounding the \u2018posterior\u2019 attachment disk (Van As et al., 1999). The ultrastructure of these somatic structures is highly complex and not similar to any of the dikinetid structures so far described (Da Silva Neto, 1994a). The infraciliature of Subclasses Oligotrichia and Choreotrichia has only recently been the subject of detailed studies, and there is consider- able variation in somatic kinetid pattern (Fig. 7.3). Strombidiid oligotrichs typically have a girdle kinety that may be composed of monokinetids in Strombidium species (Agatha, 2004a, 2004b; Lynn, Montagnes, & Small, 1988) or dikinetids (Lynn & Gilron, 1993; Petz & Foissner, 1992). The ventral kinety has at least a posterior portion that is always composed of dikinetids (Agatha, 2004a, 2004b; Lynn & Gilron, 1993; Lynn et al., 1988). There has been no ultrastructural study of these somatic kinetids . Choreotrichs are also variable in somatic kinetid structure. Although Strombidinopsis spe- cies typically have somatic dikinetids distributed in bipolar somatic kineties (Fig. 7.3) (Lynn et al., 1991c), tintinnids can have both monokinetids and dikinetids in their somatic kineties (Fig. 7.3) (Agatha & Strüder-Kypke, 2007; Choi et al., 1992; Foissner & Wilbert, 1979; Laval-Peuto & Brownlee, 1986). Among other aloricate choreot- richs , Strobilidium species have somatic monoki- netids while Leegaardiella and Lohmanniella have somatic dikinetids (Agatha & Strüder-Kypke, 2007; Lynn & Montagnes, 1988; Montagnes & Lynn, 1991; Petz & Foissner, 1992). Strobilidium species have ciliated somatic monokinetids whose cilia extend out under a cortical ridge, parallel to the cell surface (Fig. 7.3) (Grim & Halcrow, 1979); The kinetid appears to have a bilayered transverse ribbon composed of an anterior and posterior row of microtubules (Grim, 1987). Corliss (1979) classified members of our Subclasses Hypotrichia and Stichotrichia in the Order Hypotrichida while Tuffrau and Fleury (1994) placed them both in their Class HYPOTRICHEA . This view is based on the strong resemblances in the global patterning of the infraciliatures of both groups: a ventral infraciliature of scattered cirri and a dorsal infraciliature of widely spaced files of dikinetids. Marginal cirri may be distributed along the body edges, delimiting the dorsal and ventral surfaces. Ventral cirri can be arranged in anterior- posterior files (e.g., Urostyla , Kahliella , Plagiotoma ) or more asymmetrically scattered (e.g., Diophrys , Euplotes , Oxytricha , Stylonychia ) (Figs. 7.2, 7.4). Small and Lynn (1985) emphasized that the subtle differences in kinetid structure meant that these two groups were not closely related, and they separated them into the Subclasses Hypotrichia and Stichotrichia , even placing them in separate classes (see above) while Fleury et al. (1985b) had placed them in separate suborders. Division morphogen- esis in hypotrichs and stichotrichs is also different (see below) while SSUrRNA gene sequences sepa- rate them at some distance from each other (e.g., Bernhard et al., 2001). The dorsal dikinetids of hypotrichs are characterized as follows: a ciliated anterior kinetosome with a tangential transverse ribbon , probably near triplets 3-5 and sometimes a single postciliary microtubule ; a posterior kineto- some with a short condylocilium , a divergent postciliary ribbon, and a laterally-directed, striated kinetodesmal fibril at triplets 6, 7 (Fig. 7.5) (Lenzi & Rosati, 1993; Lynn, 1991; Rosati, Verni, Bracchi, & Dini, 1987; Wicklow, 1983). Lasiosomes , whose function is not known, may be associated with the axonemal base of the anterior cilium while ampules may surround the kinetid in some euplotids (e.g., Ruffolo, 1976a; Görtz, 1982a). The stichotrich dorsal dikinetid is much more variable but typically is characterized as: the ciliated anterior kinetosome bears a tangential transverse ribbon ; the non-cili- ated posterior kinetosome, if present, bears a small divergent postciliary ribbon and typically loses its kinetodesmal fibril during development (Fig. 7.5) (Fleury et al., 1986; Görtz, 1982a; Grimes & Adler, 1976; Lynn, 1991). The ventral somatic kinetids of hypotrichs and stichotrichs are typically polykinetids, called cirri . These complex ciliary structures enable the complex movements of hypotrichs and stichotrichs, allow- ing them to rapidly dart a short distance forward, quickly withdraw, and change directions rapidly (e.g., Erra, Iervasi, Ricci, & Banchetti, 2001; Ricci, 1990). However, cirri undoubtedly develop from the assembly of dikinetid units (see Division and Morphogenesis ;