Pré-visualização25 páginas
McLaughlin, & Harrison, 1959; McLaughlin, Johnson & Bradley, 1974) and non- axenic (Finley et al., 1959; Vacchiano, Kut, Wyatt, & Buhse, 1991) techniques have been developed for cell biological research on peritrichs . Soldo and Merlin (1972, 1977) have successfully developed an axenic culture medium for marine scuticocili- ates , and this has enabled the cultivation of some species, reported as parasitic on shellfish and fish (Cawthorn et al., 1996; Crosbie & Munday, 1999; Iglesias et al., 2003; Messick & Small, 1996). There has not yet been a successful axenic cultiva- 280 15. Subphylum 2. INTRAMACRONUCLEATA: Class 9. OLIGOHYMENOPHOREA tion of the fish parasite Ichthyophthirius , although Nielsen and Buchmann (2000) succeeded in induc- ing trophont transformation using a fish tissue cul- ture cell line. Mizobuchi, Yokoigawa, Harumoto, Fujisawa, and Takagi (2003) have recently dem- onstrated that hydrogen peroxide is the toxic sub- stance in the infusion of wheat grass powder used to grow Paramecium . This substance, which may also inhibit the growth of other ciliates, is detoxi- fied by catalase excreted by bacteria , explaining why \u201cconditioned\u201d media may be more successful in cultivating some ciliate species. Molecular phylogenies generally recover an oli- gohymenophorean clade with strong bootstrap sup- port (Baroin-Tourancheau, Villalobo, Tsao, Torres, & Pearlman, 1998; Miao et al., 2001; Sánchez- Silva, Villalobo, Morin, & Torres, 2003; Strüder- Kypke et al., 2000b). Sánchez-Silva et al. (2003) Fig. 15.1. Life cycles of oligohymenophoreans . A A hymenostome , like Tetrahymena paravorax , can transform between a microstome bacterivore and a macrostome carnivore depending upon food availability. (after Corliss, 1973.) B The theronts of the ophryoglenine Ichthyophthirius multifiliis seek out the epithelium of a freshwater fish host, burrow underneath as a phoront , and then begin to grow as a trophont . Trophonts later drop off the fish and undergo palintomy to produce sometimes more than 1,000 theronts . (after Lynn & Small, 2002.) C The ophryogle- nine Ophryoglena typically feeds on dead or moribund invertebrates. After feeding, the trophont becomes a proto- mont , encysts as a tomont to undergo palintomy and produce theronts , the dispersal stage that seeks out other prey. (after Canella & Rocchi-Canella, 1976.) 15. Subphylum 2. INTRAMACRONUCLEATA: Class 9. OLIGOHYMENOPHOREA 281 282 15. Subphylum 2. INTRAMACRONUCLEATA: Class 9. OLIGOHYMENOPHOREA argued that contemporary oligohymenophoreans may all have arisen from an ancestor with a devi- ant nuclear genetic code for glutamine/glutamate. Nevertheless, there are no strong morphological synapomorphies for the class. The somatic kinetid has been typified as a monokinetid with a radial transverse microtubular ribbon and a typically well-developed kinetodesmal fibril (Lynn, 1981, 1991). However, inclusion of the peniculines in the class presents an exception to this rule. As noted above, the oral structures typically include three or four oral polykinetids on the left side of the oral cavity and a paroral of dikinetids on the right. Yet, representatives of the Subclass Astomatia entirely lack an oral apparatus while those in the Subclass Apostomatia have highly modified oral structures, albeit with presumed homologies to their less modified kin (Bradbury, 1989). We have relied on the molecular phylogenies to support the class and presume that modifications in morphology away from the type are manifestations of evolutionary divergence. The class includes six subclasses: Subclass Peniculia , Subclass Scuticociliatia , Subclass Hymenostomatia , Subclass Peritrichia , Subclass Apostomatia , and Subclass Astomatia . 15.1 Taxonomic Structure Corliss (1979) divided the Class OLIGOHY\u2013 MENOPHOREA into two subclasses \u2013 Subclass Hymenostomata and Subclass Peritrichia . He excluded the apostomes from this class, placing them as an order within the Class KINETOFRAGMINOPHORA . Bradbury (1989) has demonstrated a paroral-like kinetid arrange- ment in the apostomes . On this basis, and together with similarities in the somatic kinetid (see below ), we have transferred the apos- tomes to the Class OLIGOHYMENOPHOREA . We now have sequences of the small subunit (SSU) rRNA gene of several genera of apos- tomes to confirm this transfer (J.C. Clamp et al., unpublished data 2008). Our system includes all of the subclasses that de Puytorac (1994a) rec- ognized, except for the Subclass Hysterocinetia (see below), which we conservatively retain as a group within the Subclass Scuticociliatia , awaiting molecular genetic evidence to dem- onstrate that this group is clearly so differ- ent. Thus, we outline briefly the six subclasses: (1)Subclass Peniculia ; (2) Subclass Scuticociliatia ; (3) Subclass Astomatia ; (4) Subclass Peritrichia ; (5) Subclass Hymenostomatia ; and (6) Subclass Apostomatia \u2013 and their major included groups. Small and Lynn (1981, 1985) placed the peni- culine ciliates, such as Paramecium and Frontonia , as an order in their Class NASSOPHOREA , based on similarities in the somatic kinetids, pellicular ultrastructure, and extrusomes. Molecular genetic studies on both SSUrRNA (Strüder-Kypke et al., 2000a, 2000b) and proteins (Sánchez-Silva et al., 2003) have refuted this association and confirmed the classical view that peniculines derived from the same ancestral lineage as the other oligohymeno- phorean groups. Nevertheless, these molecular data clearly confirm the distant relationship of the peniculines to other members of the class, a dis- tance supported by their morphological features, seemingly homologous to those of the nassopho- reans . The prime synapomorphies for peniculines are as follows: three oral polykinetids, called peniculi , that are aligned longitudinally in the oral cavity (Fauré-Fremiet, 1950a, 1950b); the typical, although not universal, presence of fibrous trichocysts (Didier, 1971; Jurand & Selman, 1969); and a stomatogenesis in which the parental paroral and its accompanying anarchic field produce the new oral structures (Beran, 1990; Foissner, 1996b; Yusa, 1957). We have included two orders within the subclass. The Order Peniculida , characterized by holotrichous somatic ciliation and the presence of fibrous trichocysts includes six families: the Frontoniidae , the Lembadionidae , the Maritujidae , the Neobursaridiidae , the Parameciidae , and the Stokesiidae . Since there is clear evidence, both from its distinctive girdle of somatic cilia, its lack of fibrous trichocysts (Didier; Didier & de Puytorac, 1969), and its divergent SSUrRNA gene sequence (Strüder-Kypke et al., 2000b) that Urocentrum is very divergent from other peniculines , we support the monotypic Order Urocentrida proposed by de Puytorac, Grain, and Mignot (1987) to include the Family Urocentridae . Species diversity within the genus Paramecium continues to be exhaustively analyzed (Maciejewska, 2007). Corliss and Daggett (1983) particularly focused on taxonomic and nomenclatural issues surrounding those species, previously assigned to the aurelia species complex of Paramecium . They emphasized that there is no longer a species named Paramecium aurelia in the genus Paramecium . This taxonomic arrangement had been formalized by Sonneborn (1975) after research by Tait (1970) and Allen, Farrow, and Golembiewski (1973) had demonstrated categorical differences among isoenzymes , such as esterases and dehydrogenases , in this sibling species complex . The same year, morphologically-oriented systematists had used multivariate techniques to demonstrate the separa- bility of several of these sibling species or syngens (Gates, Powelson, & Berger, 1975;