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Loxodes whose response to oxygen concentrations is modi- fied by light (Fenchel & Finlay, 1986b). Karyorelicteans are predaceous macrophages, using their filiform or vermiform bodies to crawl between the grains in the sediments in search of food. They have been recorded to ingest bacteria , Fig. 5.1. Representative genera of the Class KARYORELICTEA. The protostomatid Kentrophoros whose body in cross-section is ciliated on one surface (the right?) and harbors a \u201ckitchen garden\u201d of epibiotic bacteria on its glabrous zone (after Foissner, 1995a). The loxodid Loxodes whose ventral oral region has a paroral along its right border and an intrabuccal kinety extending posteriorly into the tube-like oral cavity. Note the bristle kinety along the ventral left surface of the cell (arrow) (after Bardele & Klindworth, 1996). The protostomatid Tracheloraphis showing its prostomial oral region and the glabrous zone bordered by the bristle kinety (After Foissner & Dragesco, 1996b). The protoheterotrichid Geleia, which is holotrichous and shows a complex oral region of dikinetid files and simple polykinetids. (after Dragesco, 1999.) 124 5. Subphylum 1. POSTCILIODESMATOPHORA: Class 1. KARYORELICTEA \u2013 The \u201cDawn\u201d diatoms (e.g., Coscinodiscus , Phaeodactylum ), both autotrophic and heterotrophic flagellates (e.g., Euglena , dinoflagellates ), other ciliates (e.g., Euplotes , Strombidium , and smaller karyorelict- eans ), and even micrometazoans, such as rotifers and copepods (Foissner, 1998b). The many species sharing an interstitial habitat probably coexist in part by partitioning food resources: different-sized Loxodes species coexist in the same lake as the larger species consumes the larger food particles (Finlay & Berninger, 1984). Conjugation is rarely observed (see Sexuality and Life Cycle below). Since it does occur in some taxa, we presume it to be an ancestral feature of the group. Cysts are not known. Thus, explaining the presumed global distribution of some of these ciliates is problematic as it is with any group that does not form resistant phases in the life cycle. 5.3 Somatic Structures The karyorelictean cell body is typically long, some- times >5,000 µm, and frequently flattened to about 5\u201310 µm in thickness. In several genera, the cell surface on which the organism \u201ccrawls\u201d is more densely ciliated (e.g., Loxodes , Kentrophoros ). The body is often pigmented, brown or yellowish, possibly due to pigmentocysts or extrusomes . The pigmento- cysts apparently have a defensive function, at least in Loxodes (Buonanno, Saltalamacchia, & Miyake, 2005). The cell surface may have a conspicuous glycocalyx , but is not underlain by a regular layer of cortical alveoli . When present, the alveoli are irregu- lar and small. Parasomal sacs have not been observed. The somatic dikinetids of these ciliates are com- posed of two kinetosomes joined by desmoses (Fig. 5.2), and oriented at 20\u201340° to the kinety axis. Both kinetosomes may be ciliated or only the anterior one. The postciliary microtubular ribbon of the posterior kinetosome is divergent, extending up to the cortex and posteriorly to overlap the ribbons of 10 or more anterior kinetids, and so forming the postciliodesma . The number of overlapping ribbons will vary depending upon the contractile state of the ciliate, as these microtubules are assumed to play the same role in cell elongation as those of Stentor (Huang & Mazia, 1975; Huang & Pitelka, 1973). It is not clear how the organization of the postciliary ribbons changes from their origin as a ribbon to the modified structure at the cell surface. There are two microtubules closest to the kinetosome followed by a ribbon of up to 20 microtubules perpendicular to the cell surface, and then a single microtubule. This 2 + ribbon + 1 pattern can be repeated for each over- lapping set (Fig. 5.2) (Klindworth & Bardele, 1996; Raikov, 1994b; Raikov & Kovaleva, 1995; Raikov, Gerassimova-Matvejeva, & de Puytorac, 1976). The postciliary microtubules are accompanied by dense material on either side near their base. The posterior kinetosome may also have a tangential transverse ribbon associated with triplets 3\u20135 (Fig. 5.2). The kinetodesmal fibril originates near triplets 5, 6, and 7 and is variable in form. It is striated and elongate in Remanella (Raikov, 1994b), striated and shovel- shaped in Loxodes (Bardele & Klindworth, 1996), and short and hooked with only a faint periodicity in Tracheloraphis (Raikov & Kovaleva, 1995) and Geleia (de Puytorac, Raikov, & Nouzarède, 1973a). The kinetodesmal fibril structure in the latter two genera is very reminiscent of Stentor \u2019s as described by Huang and Pitelka. In Loxodes, the shovel-shaped kinetodesmal fibril becomes branched, one branch of which extends to contact the postciliary ribbon of the next anterior kinetid. The anterior kinetosome has a tangential transverse ribbon associated with triplets 3\u20135. There may be ribbons of subkinetal microtubules that originate from the bases of the somatic kinetosomes and extend posteriorly beneath the kinety (Raikov & Kovaleva, 1995) or towards the left (Klindworth & Bardele, 1996). There are two kineties on the left side of Loxodes that have been interpreted to be one continuous kinety. Klindworth and Bardele (1996) have disproved this by showing that the kinetodesmal fibrils are oriented in the manner expected for two kineties: these kineties just hap- pen to abut near the anterior end and so appear to be continuous at the level of the light microscope. Until it is demonstrated otherwise by electron microscopy, we assume that the bristle kineties bordering the non-ciliated stripe in Kentrophoros are bipolar, contrary to the interpretations of Foissner (1995a, 1998b). Myonemes are arranged longitudinally and parallel to the somatic kineties in most karyorelicteans : to the right of the kinety in Tracheloraphis , to the left of the kinety in Remanella , and on both sides in Geleia . Since these ciliates are often not evenly ciliated around the body, contraction may cause Fig. 5.2. Ultrastructure of the cortex of the Class KARYORELICTEA. A Somatic dikinetids. (a) The protostomatid Tracheloraphis (after Raikov & Kovaleva, 1995). (b) The loxodid Loxodes. (after Klindworth & Bardele, 1996.) (c) The protoheterotrichid Geleia (after de Puytorac, Raikov, & Nouzarède, 1973a). B Somatic cortex of the protostome Tracheloraphis with postciliodesmata composed of overlapping ribbons in the 2 + ribbon + 1 arrangement. (Redrawn after Raikov et al., 1976.) 5.3 Somatic Structures 125 126 5. Subphylum 1. POSTCILIODESMATOPHORA: Class 1. KARYORELICTEA \u2013 The \u201cDawn\u201d the cell to become banana-shaped or roll up. In some species, transverse myonemes occur, possibly ensuring an even longitudinal contraction. The contractile vacuole system is not well- developed, except in freshwater Loxodes species, and is often absent. Extrusomes in the karyorelicteans are very diverse. Rhabdocysts have been recorded in Tracheloraphis and Kentrophoros (Raikov, 1974b), ampullocysts in Kentrophoros (Raikov), and cnidocysts and orthonematocysts in Remanella (Foissner, 1996a; Raikov, 1978, 1992, 1993). The aberrant character of karyorelictean extrusomes in relation to those of other ciliates and the apparent similarities of the cnidocysts of some karyorelicteans to the extrusomes of dinoflagellates, another alveolate group, have been used as another feature to indicate the ancestral nature of the karyorelicteans (Raikov, 1992). 5.4 Oral Structures The taxa in this class are distinguished from each other primarily on the basis of oral structures, which, as we learn more about the detailed cyto- anatomy of this group, are quite diverse. Oral kinetosomes bear cilia that are usually slightly longer than the somatic cilia, and may have simple nematodesmata,