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absent or reduced to a few pericytostomal kineto- somes; macronucleus, homomerous, band-like ; 17.3 The Ciliate Taxa to Genus 387 micronucleus, present; contractile vacuole, present; cytoproct (?); predators of peritrichs and sucto- rians or on tissues (?) of host; in marine habitats as endosymbionts in wide range of hosts, such as ascidians , barnacles , brittle stars , and tunicates ; one family. Family HYPOCOMIDAE Bütschli, 1889 (syn. Crateristomatidae ) With characteristics of order; five genera. \u2013 Crateristoma Jankowski, 1967 \u2013 Harmocoma Jankowski, 1980 \u2013 Hypocoma Gruber, 1884 \u2013 Parahypocoma Chatton & Lwoff, 1939 \u2013 Rhynchocoma Jankowski, 1975 Order Rhynchodida Chatton & Lwoff, 1939 (syns. Ancistrocomina , Rhynchodina , Sphe- nophryina ) Size, small to medium; shape, variable; free- swimming, but typically attached to the host by the oral region; somatic kineties, sometimes with non-ciliated kinetosomes, typically organized in a thigmotactic field, which may extend to cover the entire body or which may be divided in two, leaving a large part of the cell surface bare ; no posterior adhesive region ; macronucleus, vari- ably shaped, typically not in a band-form; parasites of the gills of invertebrates, commonly bivalve molluscs ; two families. Family ANCISTROCOMIDAE Chatton & Lwoff, 1939 (syns. Ancistrocominae , Cepedellidae , Hypo- comellinae , Hypocomidinae ) Size, small to medium; shape, typically pear- or banana-like with a pointed anterior end; free- swimming, but typically attached to host; somatic kineties, with thigmotactic cilia more or less developed, at least near the anterior end, tend- ing to reduction to a small anterior thigmotactic ventral field; with apical sucker ; oral ciliation, absent; macronucleus, globular to ellipsoid; micro- nucleus, present; contractile vacuole, may be present; cytoproct (?); feeding on cell contents of host tissues; in marine and freshwater habitats as parasites of invertebrates, such as polychaetes , a phoronid , and others, but found principally in the mantle cavity of molluscs ; 21 genera and one genus incertae sedis . \u2013 Ancistrocoma Chatton & Lwoff, 1926 \u2013 Anisocomides Chatton & Lwoff, 1950 \u2013 Colligocineta Kozloff, 1965 \u2013 Crebricoma Kozloff, 1946 \u2013 Enerthecoma Jarocki, 1935 \u2013 Goniocoma Chatton & Lwoff, 1950 \u2013 Heterocinetopsis Jarocki, 1935 \u2013 Holocoma Chatton & Lwoff, 1950 \u2013 Hypocomagalma Jarocki & Raabe, 1932 \u2013 Hypocomatidium Jarocki & Raabe, 1932 \u2013 Hypocomella Chatton & Lwoff, 1924 \u2013 Hypocomides Chatton & Lwoff, 1922 \u2013 Hypocomidium Raabe, 1938 \u2013 Hypocomina Chatton & Lwoff, 1924 \u2013 Ignotocoma Kozloff, 1961 \u2013 Insignicoma Kozloff, 1946 \u2013 Isocomides Chatton & Lwoff, 1950 \u2013 Kozloffiella Raabe, 1970 \u2013 Raabella Chatton & Lwoff, 1950 \u2013 Stegotricha Bower & Meyer, 1993 \u2013 Syringopharynx Collin, 1915 Incertae sedis in Family Ancistrocomidae \u2013 Cepedella Poyarkoff, 1909 Family SPHENOPHRYIDAE Chatton & Lwoff, 1921 (syns. Gargariidae , Lwoffidae , Pelecyophyridae ) Size, small to medium; shape, ovoid to elongate, flattened; except in one species, adult form or trophont unciliated, but with an infraciliature in two fields that may diverge from a central (= posterior) apex towards the ends of the body; attached to host by adhesive \u201csole\u201d and short tentacle ; reproduction, isotomic fission or by bud- ding; larval form, typically ciliated with kinetal pat- tern reminiscent of ancistrocomids; macronucleus, globular to elongate band-form; micronucleus, present; conjugation, often occurring epidemically; contractile vacuole, present; cytoproct (?); feed- ing on cell contents of host tissues; in marine and freshwater habitats as parasites in the mantle cavi- ties of bivalve molluscs ; three genera. \u2013 Gargarius Chatton & Lwoff, 1934 \u2013 Pelecyophrya Chatton & Lwoff, 1922 388 17. The Ciliate Taxa Including Families and Genera \u2013 Sphenophrya Chatton & Lwoff, 1921 Incertae sedis in Order Rhynchodida \u2013 Lwoffia Kozloff, 1955 Subclass Suctoria Claparède & Lachmann, 1858 (syns. Acinet[e] , Acinetaria , Acinetina , Acinet[o]idea , Actinifera , Actinosuctorifera , Atricha , Dystricha , Suctorasina , Suctorea , Suctoriae , Suctorifera , Suctoriorida , Tentaculifer[id]a , Ten- taculiferiae , Toxistomia p.p .) Size, small to large; shape, variable, from simple spheroid to flattened discs to complex branching forms; polymorphic, with free-swimming, typi- cally ciliated larval form and typically sessile, adult form, usually non-ciliated, although with an infra- ciliature; alveoli, well-developed, underlain by a thick epiplasm; extrusomes as toxic \u201coral\u201d hapto- cysts in tips of suctorial tentacles or arrayed along the length of prehensile tentacles; oral structures as one to many multiple, rarely none, ingestatory suctorial tentacles, short (e.g., Cyathodinium , Phalacrocleptes ) or long and extensible (e.g., Rhyncheta , Rhynchophrya ), usually supported by an outer ring of microtubules and an inner set of microtubular ribbons (= the presumed phyllae) with extrusomes as haptocysts at the tips ; stalk, often present, always non-contractile, of varying length and produced by the scopuloid; migratory motile ciliated larval form or swarmer, produced by some mode of budding, but typically bearing neither tentacles nor stalk; macronucleus, homomerous; conjugation of different kinds, but frequently total with unequal conjugants; con- tractile vacuole, present; cytoproct, absent; cyst, often present; feeding primarily on other ciliates, but some species parasites of other eukaryotes; in marine, freshwater, and rarely terrestrial habitats, widespread, predominantly as ectosymbionts on diverse invertebrates, but some as endocommensals in hosts ranging from other ciliates to vertebrates; three orders. NOTE : There is as yet no strong consensus on the evolutionary diversification of the suctorians. We have remained conservative, and tried to assign taxa to the included orders based on the modes of budding proposed by Collin (1912). Kormos and Kormos (1957a) have proposed a more complex classification of budding, which Batisse (1994) has partly followed. Revisionary monographs have also been published by Jankowski (1981), Curds (1985a, 1985b, 1985c, 1986, 1987), and Matthes (1988). Dovgal (2002) has undertaken an exten- sive cladistic analysis and discussed the status of taxa at the generic level and above. In the main, we have followed Dovgal for taxonomy within the group, and strongly recommend this monograph as a starting point for future taxonomic investiga- tions. However, we do not agree with Dovgal on two major points. First, we do not recognize the class status of the suctorians . Second, we have not recognized the vermigenids as a separate group, and instead placed these families within the Order Exogenida , especially considering that Dovgal suggested that vermigenids may have been derived from exogenid ancestors. While a comprehensive analysis using gene sequences may prove one of these schemes most appropriate, the first small subunit rRNA gene sequences suggest that Collin\u2019s (1912) system may have validity (Snoeyenbos- West et al., 2004). Order Exogenida Collin, 1912 (syns. Allantosomatida p.p ., Asteriferina , Dendrosomidida p.p ., Ephelophagina , Ephelotida , Ephelotina , Exogenea , Exotropida , Metacinetida p.p ., Nemertodendrina p.p ., Oligostomatida p.p ., Ophryocephalida p.p ., Ophryodendrida , Ophryodendrina , Paracinetida , Paracinetina , Phalacrocleptida p.p ., Podophryida , Podophryina , Spelaeophryida , Spelaeophryina , Stylostomatina p.p ., Thecacinetina , Tomogenea , Urnulida p.p ., Vermigemmida , Vermigenea , Vermigenia ) Size, small to large; shape, diverse; often stalked