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209 Abstract Phyllopharyngeans are divided into four subclasses, only one of which is dominated by free- living forms. The Subclass Cyrtophoria includes common members of bio\ufb01 lm communities, from sea ice in Antarctica to waste water treatment plants. The Chonotrichia, Rhynchodia, and Suctoria are typically found as symbionts: chonotrichs are ses- sile ectocommensals on the appendages of crusta- ceans; rhynchodians are ectoparasites on the gills of bivalves; and suctorians are epibionts on metazoans, from crustaceans to turtles. The cyrtophorians and chonotrichs have heteromerous macronuclei, which suggests that they might be united into a larger tax- on, and this is supported by small subunit rRNA gene sequences. The somatic kinetid is a monoki- netid with a distinctly shaped and laterally directed kinetodesmal \ufb01 bril, and is underlain by sub kinetal microtubules. The cytopharyngeal apparatus is lined by microtubular ribbons, called phyllae, from which the class derives its name. Cyrtophorians and chonotrichs feed on bacteria and small algae. Rhynchodians use a single sucker to ingest cyto- plasm of host cells, while suctorians typically have multiple sucking tentacles to catch primarily other ciliates. Division in cyrtophorians is characterized as merotelokinetal, but in chonotrichs and suctori- ans is characterized by specialized forms of bud- ding. The macronuclear DNA is apparently highly fragmented, and as in the spirotrichs, differentiates after the formation of polytene chromosomes. Keywords Internally eliminated sequences, poly- tene chromosome The ciliates included in this class are very diverse in body form, influenced by the fact that three of the four subclasses are symbionts of metazoans. Members of the only free-living group, the cyrtophorians , range from small to medium-sized. Their oral region has a prominent cytopharyn- geal basket or cyrtos , which gave rise to their name (Corliss, 1979). Typically dorsoventrally flattened, they are conspicuous members of the Aufwuchs or biofilm communities of marine and freshwater habitats to which they attach with their ventral ciliature and attachment organelles (Deroux, 1976a, 1976b, 1977). The chonotrichs are typically found on the appendages of a variety of crustaceans , and range from 40\u2013350 µm in length (Fernández-Leborans, 2001; Jankowski, 1973b; Mohr, Matsudo, & Leung, 1970). As the name suggests, their body is cone-like, particularly at its apex where the ciliature is enclosed in a cone- like structure. The rhynchodids are very small to small (i.e., 20\u201350 µm in length), typically found on the gills and within the mantle cavity of molluscs and other invertebrates (Chatton & Lwoff, 1949, 1950; Raabe, 1967, 1970a, 1970b) where they attach to the tissues with a single tentacle-like oral structure. The suctorians , some, like Dendrosoma radians , as large as 5 mm, are epibionts on a wide range of metazoans from crustaceans (Fernández- Leborans & Tato-Porto, 2000a) to turtles (Matthes, 1988). Called tentaculiferans because of their feeding tentacles and \u201c acinétiens \u201d because they apparently lacked ciliated kineties, they have been related to heliozoans and hydrozoans at various times. Careful study of their complete life Chapter 10 Subphylum 2. INTRAMACRONUCLEATA: Class 4. PHYLLOPHARYNGEA \u2013 Diverse in Form, Related in Structure 210 10. Subphylum 2. INTRAMACRONUCLEATA: Class 4. PHYLLOPHARYNGEA cycle showed that they were indeed heterokaryotic unicells or ciliates, had ciliated kineties in the dispersal swarmer stage, and underwent conjugation (Collin, 1912; Guilcher, 1951; Kormos & Kormos, 1957a, 1957b, 1958). Phyllopharyngeans are typi- cally not dominant members in microbial com- munities. However, cyrtophorians , particularly in the genus Chilodonella , are important indicators of water quality (Foissner, 1988a) and can be troublesome ectoparasites on the skin and gills of fishes in aquaculture settings (Hoffman, 1988). Standardization of culture methods has meant that some Chilodonella species have become model organisms for studying the biology of this class (Radzikowski & Golembiewska, 1977). Small and Lynn (1981) were the first to recog- nize this group as a class within the phylum, and united these four groups based on the structure of the somatic kinetid and the presence of phyllae or leaf-like ribbons of microtubules surrounding the pharyngeal tube. This gives rise to the class name PHYLLOPHARYNGEA , which is derived from phyllos , Greek, meaning leaf and pharynx , Greek, meaning mouth. Guilcher (1951) demonstrated the affinities of cyrtophorians and chonotrichs in her studies of division morphogenesis of these organisms. Ultrastructural data then prompted de Puytorac et al. (1974b) to include these two groups in their Superorder Phyllopharyngidea . De Puytorac, Grain, Legendre, and Devaux (1984) con- firmed this using a numerical phenetic analysis and further supported the decision of Small and Lynn (1981) to unite these four groups into a class. The Class PHYLLOPHARYNGEA must have originated at least in the Paleozoic Era . Mohr (1966) has argued that the chonotrichs themselves must have diverged not later than the Tertiary Period , some 225 million years ago. The class is established as monophyletic based on two strong synapomor- phies (Small & Lynn, 1981). First, the structure of the somatic monokinetids is highly conserved with a distinctively shaped, laterally directed kinetodes- mal fibril and subkinetal microtubules underlying the somatic kinetosomes. These monokinetids are observed in the somatic regions of the trophonts of cyrtophorians , chonotrichs , and rhynchodians , and in the kineties of the dispersive swarmers or buds of chonotrichs and suctorians . Second, the phar- ynx, or at least ingestatory structures in the case of the tentacles of suctorians , is lined by ribbons of arm-bearing microtubules called phyllae . These ribbons are often disposed in a somewhat radial fashion when the ciliate is not feeding. The phyllae lining the cytopharynx of cyrtophorians lie inside a palisade of rod-like nematodesmata, which together form the cyrtos or cytopharyngeal basket . Cyrtophorians and chonotrichs possess heteromer- ous macronuclei , a synapomorphy that unites them as a clade (Grell & Meister, 1982a), which might be recognized taxonomically in the future. The first molecular phylogeny of phyllopharyngeans supports these cytological affinities, strongly dem- onstrating that the chonotrich Isochona groups well within the cyrtophorine clade (Snoeyenbos-West, Cole, Campbell, Coats, & Katz, 2004). 10.1 Taxonomic Structure Corliss (1979) placed the four subclasses that we now include in this class in two orders, the Order Hypostomata and Order Suctoria in the Class KINETOFRAGMINOPHORA . The Hypostomata , which included cyrtophorines , chonotrichs , and rhynchodines , also included what we now consider to be unrelated forms. Small and Lynn (1981) emphasized the features of the somatic kinetid (i.e., a distinctively shaped, laterally directed kinetodes- mal fibril and subkinetal microtubules underlying the somatic monokinetids) and the similarities in the oral structures (i.e., phyllae lining cytopharynx) as shared derived characters to establish the Class PHYLLOPHARYNGEA , a name that had been proposed by de Puytorac et al. (1974b) to include only cyrtophorines and chonotrichs. De Puytorac et al. (1984) later supported the class as envisioned by Small and Lynn (1981). Lynn and Small (1997, 2002) have maintained these subclass assignments. Leipe, Bernhard, Schlegel, and Sogin (1994) demonstrated that the cyrtophorian Trithigmostoma and the suctorian Discophrya formed a strongly supported clade based on sequence analyses of the small subunit ribosomal