Pré-visualização13 páginas
and somatic kinetids with postcilio- desmata (Fig. 4.7) in which the postciliary micro- tubular ribbons are separated by only a single microtubule (see Chapter 6 ). Oral structures in the karyorelicteans are quite variable, ranging from prostomial with simple circumoral ciliature to ventrostomial with developed paroral and adoral ciliature . Heterotricheans , like Stentor , are virtually all bearers of a paroral and an elaborately developed adoral zone of polykinetids (Figs. 4.3, 4.4). The Subphylum Intramacronucleata includes the remaining nine classes, each of which will Fig. 4.3. Stylized drawings of genera representative of each class in the Phylum Ciliophora: Loxodes \u2013 Class KARYORELICTEA ; Stentor \u2013 Class HETEROTRICHEA ; Protocruzia , Euplotes \u2013 Class SPIROTRICHEA ; Metopus \u2013 Class ARMOPHOREA ; Didinium \u2013 Class LITOSTOMATEA ; Chilodonella \u2013 Class PHYLLOPHARYNGEA ; Obertrumia \u2013 Class NASSOPHOREA ; Colpoda \u2013 Class COLPODEA ; Plagiopyla \u2013 Class PLAGIOPYLEA ; Holophrya \u2013 Class PROSTOMATEA ; and Tetrahymena \u2013 Class OLIGOHYMENOPHOREA 4.1 Taxonomic Structure 95 96 4. Phylum CILIOPHORA \u2013 Conjugating, Ciliated Protists with Nuclear Dualism Fig. 4.4. Scanning electron micrographs of ciliate diversity. A\u2013C Class HETEROTRICHEA . Blepharisma ( A ), Fabrea ( B ), and Stentor ( C ). D\u2013I Class SPIROTRICHEA . The oligotrich Strombidium ( D ), the tintinnids Dictyocysta ( E ) and Tintinnopsis ( F ), the stichotrich Stylonychia ( G ), and the hypotrichs Euplotes ( H ) and Uronychia ( I). (Micrographs courtesy of E. B. Small and M. Schlegel.) be briefly characterized here (Table 4.1). Lynn (2004) has noted that four of the classes \u2013 the LITOSTOMATEA , PHYLLOPHARYNGEA , NASSOPHOREA , and COLPODEA \u2013 are strongly supported by both molecular and morpholo gical characteristics. The remaining five classes \u2013 the SPIROTRICHEA , ARMOPHOREA , PLAGIOPYLEA , PROSTOMATEA , and OLIGOHYMENOPHOREA \u2013 have less strong support from molecules and morphology. Two of these latter five, the ARMOPHOREA and PLAGIOPYLEA , are only supported by molecules, and hence called \u201criboclasses\u201d (Lynn, 2004). Spirotricheans , like Protocruzia , Euplotes , Strombidium , Dictyocysta , Tintinnopsis , Stylonychia , and Uronychia (Figs. 4.3, 4.4, Table 4.1), are a diverse group, typically having a paroral and a well-developed adoral zone of polykinetids . The class is rarely strongly supported as a clade by molecular phylogenetics. Most of the taxa exhibit somatic dikinetids with a poorly developed kineto- desmal fibril (Fig. 4.7) and two of the included subclasses, the Hypotrichia and Stichotrichia , have compound ciliary organellar complexes called cirri (Figs. 4.3, 4.4, 4.7). The strongest morphological synapomorphy for the class is the replication band that occurs during macronuclear DNA S-phase (see Chapter 7 ). The replication band has been confirmed in members of all subclasses except the two monotypic Subclasses Protocruziidia and Phacodiniidia . The phacodiniids are undoubtedly spirotrichs by their placement well within the spirotrichean clade using the small subunit rRNA ( SSUrRNA ) molecule (Shin et al., 2000). The situ- ation for Protocruzia , also the only member of its subclass, is more uncertain as it is typically placed as the basal lineage in the spirotrich branch. We have placed protocruziids in this class because they are tenuously associated with it by SSUrRNA gene sequences (see Chapter 16 ). However, they may warrant separate class status in the future because their histone sequences are divergent from other spirotrichs (Bernhard & Schlegel, 1998), and they exhibit a unique mode of macronuclear division (Ammermann, 1968; Ruthmann & Hauser, 1974). Armophoreans , like the armophorid Metopus and the related clevelandellid Nyctotherus (Figs. 4.3, 4.5, Table 4.1), are strongly supported only by SSUrRNA gene sequences (van Hoek et al., 2000b). The somatic kinetids of the two subclasses within this class are quite different (Fig. 4.7; and see Chapter 8 ). However, Villeneuve-Brachon (1940) speculated that these ciliates might be related to each other, a view later endorsed by Jankowski (1968b) and Albaret (1975). Both free-living and endosymbiotic armophoreans are found in anoxic or close to anoxic environments and all are presumed to have hydrogenosomes . Future research on armo- phorean hydrogenosomes may reveal synapomor- phies in their anaerobic metabolism that may more strongly confirm this class. Litostomateans , like the haptorians Didinium and Dileptus and the trichostomes Isotricha , Entodinium , and Ophryoscolex (Figs. 4.3, 4.5, Table 4.1) are strongly supported by both SSUrRNA gene sequences and by features of the somatic kinetid , which is a monokinetid with two trans- verse ribbons (Fig. 4.7; and see Chapter 9 ). The two included subclasses may not be mono phyletic: it now appears the haptorians may be a para- phyletic group (Strüder-Kypke, Wright, Foissner, Chatzinotas, & Lynn, 2006). Phyllopharyngeans , like the cyrtophorians Chilodonella and Trithigmostoma and the suctorian Podophrya (Figs. 4.3, 4.6, Table 4.1), form a diverse group, strongly supported by both SSUrRNA gene sequences and by features of the somatic kinetid , which is a somatic monokinetid that has a laterally- directed kinetodesmal fibril and whose kineto- somes are underlain by subkinetal micro tubules (Fig. 4.7; and see Chapter 10 ). A significant feature of the phyllopharyngean oral apparatus is a set of radial ribbons of microtubules that support the cytopharynx, the phyllae . Nassophoreans , like Obertrumia (Fig. 4.3, Table 4.1), are also strongly supported by both SSUrRNA gene sequences and by features of the somatic kinetids, which are monokinetids that can be linked as dikinetids by filaments near the base of the transverse microtubular ribbon (Fig. 4.7; and see Chapter 11 ). In addition, the cytopharyngeal basket or nasse of these ciliates exhibits a suite of characters not found together in any other class. Colpodeans , like Colpoda (Figs. 4.3, 4.5, Table 4.1), are typically well supported by both SSUrRNA gene sequences and by features of the somatic kinetids, which are dikinetids whose pos- terior kinetosomes have well-developed transverse microtubular ribbons extending posteriorly along the kinety, forming the transversodesma or LKm fibre (Fig. 4.7; and see Chapter 12 ). Prostomateans , like Holophrya and Coleps (Figs. 4.3, 4.5, Table 4.1), are not strongly supported by molecular signals, but this may in part be due to the low taxon sampling for this group. Their somatic kinetids show similarities to those of the next three classes (Fig. 4.7), and it is only in the details of their oral structures and stomatogenesis that the group may be distinguished (see Chapter 13 ). Plagiopyleans , like Plagiopyla (Fig. 4.3, Table 4.1), are strongly supported by SSUrRNA gene sequences even though the taxon sampling is low. Nevertheless, this is the second \u201c riboclass \u201d within the phylum because there is no strong synapo- morphy for the group. The somatic kinetids are similar to those of the Classes PROSTOMATEA and OLIGOHYMENOPHOREA , showing a well- developed anteriorly-directed kinetodesmal fibril and a radially-oriented transverse microtubular ribbon (Fig. 4.7). A remarkable recent discovery 4.1 Taxonomic Structure 97 98 4. Phylum CILIOPHORA \u2013 Conjugating, Ciliated Protists with Nuclear Dualism is the indication that odontostomatids , represented by Epalxella , may form a third clade within this class (Stoeck, Foissner, & Lynn, 2007) (see Chapter 14 ). Oligohymenophoreans , like the peniculines Paramecium and Lembadion , the hymenostomes Tetrahymena and Glaucoma , and the peritrichs