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to demonstrate affinities with the caudal cilium complex of oligohymenopho- reans . The larger plagiopylids and sonderiids are typically holotrichous and densely ciliated (Fig. 14.1). Paraplagiopyla , if truly a plagiopylean , is an exception as its somatic kineties are restricted to a narrow furrow that extends around the edges of the flattened cell (Thurston & Grain, 1971). The somatic ciliature of odontostomatids is typically reduced to anterior and posterior cirrus-like tufts, although the infraciliature probably persists as non- ciliated kinetosomes (Fig. 14.2). Only four studies have been published on which to base the description of the cortical ultrastructure of plagiopyleans (Berger & Lynn, 1984; Detcheva et al., 1981; de Puytorac et al., 1985; Schrenk & Bardele, 1991). The plasma membrane is covered by a thin glycocalyx , which can appear somewhat granular (de Puytorac et al., 1985). The alveoli in plagi- opylids are well developed and lie on a thin epiplasmic layer . Schrenk and Bardele (1991) claimed that the alveolar layer is absent in the odontostomatid Saprodinium in which the cell membrane is underlain only by a thick epiplasmic layer . The cortex is ridged with kinetosomes lying between the ridges in trimyemids and at the tops of the ridges in plagiopylids . The kinetids of plagiopyleans can still only be tentatively characterized, and they differ dra- matically between plagiopylids and odontosto- matids (Fig. 14.3). However, it now appears that the characterization of the plagiopylid kinetid by Berger and Lynn (1984) was incorrect, and that the microtubular ribbon they interpreted as an unusual, anteriorly-directed transverse ribbon is probably a kind of basal microtubular system. The somatic kinetids are monokinetids with a divergent postcili- ary ribbon that extends into the cortical ridges. The well-developed, anteriorly-directed kinetodesmal fibril originates near triplets 5, 6, 7 (Fig. 14.3). The orientation of the transverse ribbon has not Fig. 14.1. Stylized drawings of representatives of the Order Plagiopylida in the Class PLAGIOPYLEA The plagi- opylid Plagiopyla . The sonderiid Sonderia . The trimyemid Trimyema . Note the striated band on the right side of Sonderia 14.3 Somatic Structure 273 been definitively proven, although published and unpublished micrographs (C. Bardele, personal communication 2006; D. Lynn, 2006) suggest a radial orientation adjacent to triplet 4 and a very short trajectory, underlain by dense material, into the adjacent cortical ridge (Fig. 14.3). The overall pattern is very similar to that of the hymenostomes (see Chapter 15 ). Dense material adjacent to the base of the kinetosome near triplets 2, 3 provides the origin of several longitudinally orientated 274 14. Subphylum 2. INTRAMACRONUCLEATA: Class 8. PLAGIOPYLEA microtubules that extend along the left side of the kinety in Lechriopyla . These were originally interpreted incorrectly as transverse microtubules (Berger & Lynn, 1984). A parasomal sac is found anterior to the kinetosome. The somatic kinetids of odontostomatids are also accompanied by parasomal sacs . However, odon- tostomatids have dikinetids, not monokinetids, throughout the cortex, although not all are cili- ated (Fig. 14.3) (Schrenk & Bardele, 1991; Sola, Serrano, Guinea, & Longás, 1992). The odonto- stomatid somatic dikinetids can be characterized as follows: a ciliated anterior kinetosome that has a tangential transverse ribbon of microtubules associated with triplets 4, 5; and a ciliated poste- rior kinetosome with a divergent postciliary rib- bon. Cathetodesmal-like fibrils may originate near triplet 2 on the anterior kinetosome (Fig. 14.3). Schrenk and Bardele (1991) concluded that there is no kinetodesmal fibril although there is a dense structure in the appropriate position near the pos- terior kinetosome and Sola et al. (1992) reported kinetodesmal fibrils adjacent to some anterior and posterior kinetosomes in the light microscopic description of Saprodinium . In the non-ciliated regions of the cortex, Saprodinium has its diki- netid kinetosomes without fibrillar associates and separated by extremely inflated parasomal sacs , which may be used for endocytosis (Schrenk & Bardele, 1991). An inverse kinety , whose origin is unclear, lies to the left of the oral region (Schrenk & Bardele, 1991; Sola et al., 1992). A unique feature of the cortex of most plagi- opylids and sonderiids , a feature that might suggest establishment of a subordinal category for mem- bers of these two families, is the striated band (Fig. 14.1) (Lynch, 1930). This band extends from the right side of the oral opening, in parallel with adjacent somatic kineties, sometimes turning ante- riorly before turning posteriorly to extend almost to the posterior pole. It is composed of a series of thin ridge-like lamellae of cytoplasm, about 2 µm high, overlain by flattened cortical alveoli. The walls of the striated band appear to be supported by 8\u20139 macrotubules (Berger & Lynn, 1984). The function of the striated band is unknown. Plagiopylids and sonderiids have conspicuous rod-shaped extrusomes , which may be up to 20 µm Fig. 14.2. Stylized drawings of representatives of the Order Odontostomatida in the Class PLAGIOPYLEA . The discomorphellid Discomorphella . The epalxellid Saprodinium in length (Fauré-Fremiet & Tuffrau, 1955). On extrusion, the matrix extends as a striated rod from a retained cylindrical envelope (Berger & Lynn, 1984). Trimyemids have spheroidal muco- cysts (Baumgartner et al., 2002; Detcheva et al., 1981) while Plagiopyla may also have some Fig. 14.3. A Schematics of the somatic kinetids of the Class PLAGIOPYLEA . ( a ) Monokinetid of Plagiopyla . ( b ) Monokinetid of Trimyema . ( c ) Dikinetid of Saprodinium (from Lynn, 1981, 1991). B Somatic cortex of a typical plagiopylid based on the somatic cortex of Plagiopyla and Lechriopyla 14.3 Somatic Structure 275 276 14. Subphylum 2. INTRAMACRONUCLEATA: Class 8. PLAGIOPYLEA smaller extrusomes (de Puytorac et al., 1985). Mucocysts have not been observed in odontosto- matids (Schrenk & Bardele, 1991). Plagiopyleans do not have mitochondria, but rather \u201cmicrobodies\u201d without cristae that are now known to be hydrogenosomes (see Life History and Ecology ) (Goosen et al., 1990; Zwart et al., 1988). A contractile vacuole and a cytoproct are typi- cally found in the posterior one-third of the cell. 14.4 Oral Structures The oral structures divide the plagiopyleans into three groups \u2013 the odontostomatids , the trimyem- ids , and the sonderiids and plagiopylids (Figs. 14.1, 14.2). Whether detailed and careful ultrastructural investigations will eventually reveal homologies, at this stage we must treat them quite separately. Odontostomatids have a small and complex oral cavity with a reduced number of oral polykinetids , typically less than a dozen (Schrenk & Bardele, 1991; Sola et al., 1992; Tuffrau, 1992). They are composed of three rows of kinetosomes, which are hexagonally packed, but only the oral polykinetid closest to the cytostome has fibrillar associates that are interpreted as postciliary ribbons (Schrenk & Bardele, 1991). These latter authors speculated that the oral region of Saprodinium , and perhaps other odontostomatids , is in an inverse orientation, but this will have to await morphogenetic studies. Odontostomatids may also have two files of paroral cilia (see Sola et al., 1992; Tuffrau, 1992), but this has not been confirmed by electron microscopy (Schrenk & Bardele, 1991). The trimyemids have always been classified among ciliates with a simple oral ciliature and oral apparatus. It is now certain that they have at least an outer row of kinetosomes with kinetodesmal