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to those in cyrtophorians . This kinety is accom- panied by two or three inverted somatic kineties, which were presumably carried into this orienta- tion during division morphogenesis . Distinct oral kinetids have not been found in other chonotrichs , although a puzzling X-field has been described in Spirochona . Fahrni (1982) concluded that this was not likely \u201coral\u201d in nature. Chonotrichs have lost the oral nematodesmata and retained only the phyllae with which are associated the elongated cytopharyngeal tubules (Fahrni; Grain & Batisse; Karadzhan, 1976). Clearly, this small sampling of chonotrichs gives us only partial insight into the structural diversity of the oral region of these ciliates. Rhynchodians have also been little studied by modern techniques. There is only a handful of studies on electron microscopy. Lom and Kozloff (1968) first demonstrated that these ciliates have a \u201csuctorial\u201d tube composed of arm-bearing microtu- bules or phyllae radially disposed as in other phyl- lopharyngeans . This basic structure was also found in the hypocomid Hypocoma (Grell & Meister, 1982a, 1983). These studies provided the interest- ing revelation that the phyllae were surrounded by an outer \u201cring\u201d of microtubules, making the hypocomid \u201csuctorial\u201d tube structurally identical to a suctorian tentacle (see below). Grell and Meister (1982a, 1983) also described elongated extrusomes called haptotrichocysts within the tube lumen. These presumably function like the haptocysts of suctoria (see below), although we have no direct evidence for this in hypocomids . Food vacuoles are observed in the suctorial tube and sometimes in the cytoplasm of rhynchodians . However, it is not yet clear how they feed. It is safe to say that the most-studied body part of the suctorians has been their tentacles . Given the similarities in the ultrastructure of the tentacle to the cytopharyngeal components of other phyllopharyn- geans , we can now conclude that suctorian tentacles are a very specialized cytostome- cytopharyngeal apparatus . However, suctorians are unusual among ciliates in that they can be considered polystoma- tous or many-mouthed. A few suctorians have only one or two tentacles (e.g., Acinetopsis \u2013 Grell & Meister, 1982b; Rhyncheta \u2013 Hitchen & Butler, 1972). Most have many tentacles regularly distrib- uted over the body surface or clustered together in fascicles , sometimes borne on very elongate projec- tions of the body called actinophores. The tentacle is an extension of the cell with a thinner glycocalyx layer on the plasma membrane and a much thinner epiplasm than the cell body. Intrinsic movements of the tentacle include bending, repeated short exten- sions and retractions, and complete retraction (e.g., see Grell & Meister, 1982b; Hitchen & Butler, 1973a). Tentacles retract when electrically stimu- lated and in elevated concentrations of external Ca 2 + (Hackney & Butler, 1981a; Hackney, AL-Khazzar, & Butler, 1982). The microtubular axoneme of retracted tentacles is not changed, but glycerinated models suggest that actin-like filaments in the epi- plasm may be the contractile elements (Hackney & Butler, 1981b). Elongation of tentacles may occur quite rapidly, and depending upon the suctorian may involve assembly of the axonemal microtu- bules , which may have been disassembled during retraction (Hauser & van Eys, 1976). The tentacle tips of many suctoria are swollen or capitate and are loaded with haptocysts (e.g., Mogensen & Butler, 1984; Spoon, Chapman, Cheng, & Zane, 1976). Most suctorians can capture ciliates but a rare few cannot (e.g., Choanophrya \u2013 Hitchen & Butler, 1973a). Bardele and Grell (1967) and Rudzinska (1965, 1970) provided the first ultrastructural evidence of the feeding process in suctorians , implicating the haptocysts in attachment of predator to prey and the role of the axonemal microtubules in transport of food vacuoles into the cell\u2019s endoplasm. Later research confirmed the existence of arms on the inner microtubular lamellae or phyllae , confirm- ing that the mechanism of food vacuole membrane transport was likely the same in suctorians as it was in other phyllopharyngeans (Bardele, 1974; Rudzinska, 1973; Tucker, 1974). Suctorian phyllae are surrounded by an outer set of microtubules, which may form a complete ring or be separated into several ribbons, ranging from around 20 to over 100 microtubules (Batisse, 1994b; Lynn & Foissner, 1994). These two sets of microtubules are helically disposed. A complex set of movements at the time of contact between predator and prey, possibly involving contraction of the epiplasm and sliding of the microtubules, expands the tentacle tip to expose the haptocysts (Hauser & van Eys, 1976; Tucker & Mackie, 1975). Haptocysts enable the \u201cgluing\u201d of the predator to the prey, likely without fusion of the plasma membranes of the two ciliates (Benwitz, 1984). Haptocyst discharge probably makes the suctorian tentacle refractory to subsequent prey capture (MacKeen & Mitchell, 1977), a prediction that has been confirmed by a mathematical model (McNair, 1979). Haptocysts develop in associa- tion with the endoplasmic reticulum in the cell body. Unlike larger extrusomes (e.g., toxicysts , mucocysts ), they differentiate synchronously in groups of over 20 within one vesicle (Benwitz, 1982). They are then transported on the outside of the tentacle axoneme up to the tentacle tip. Large numbers of osmiophilic granules, dense bodies , or solenocysts are also found within the lumen of non- feeding tentacles and are also transported upwards beneath the pellicle but outside of the axoneme of feeding tentacles (Bardele & Grell, 1967; Grell & Meister, 1982b). These dense bodies are thought to be primary lysosomes as they are positive for acid phosphatase (Rudzinska, 1974). They may also contain calcium deposits (Hackney & Butler, 1981c). The prehensile or capturing , but not inges- tatory, tentacles of Ephelota , for example, have batteries of haptocysts along their length, remind- ing one of the tentacles of Hydra with its batteries of nematocysts (Grell & Benwitz, 1984). Tentacle morphogenesis may occur throughout the life of a suctorian as tentacles can be torn off by prey during unsuccessful captures, while new tentacles may be continually added as the cell body grows in size (e.g., Hull, 1954; Hitchen & Butler, 1973b). Tentacle morphogenesis has only been described in two suctorians . In both cases, a single non-ciliated kinetosome is associated with the early formation of a microtubule-organizing center around which the tentacle axoneme assembles (Curry & Butler, 1976; Hitchen & Butler). From where do these non-ciliated kinetosomes originate and how is ten- tacle pattern and assemblage determined? A discussion of the suctoria would not be com- plete without mention of three unusual ciliates that are now recognized as members of this sub- class, primarily based on ultrastructural studies. In historical order, Phalacrocleptes , recognized as a ciliate by its nuclear dimorphism , is a non-ciliated ciliate that feeds on the cilia of the pinnules of the sabellid polychaete Schizobranchia (Kozloff, 1966)! Lom and Kozloff (1967) described \u201c ten- tacles \u201d about 0.5 µm in length, each containing one haptocyst that is used to attach the ciliate to an annelid cilium, whose cytoplasm is presum- ably ingested! Cyathodinium is a puzzling cili- ate found in the cecum of the guinea pig Cavia (Paulin & Corliss, 1964). Its endosprits turned out to be short tentacles containing haptocysts (Paulin & Corliss, 1969). This raises the ques- tion \u2013 is the permanently ciliated Cyathodinium a neotenous suctorian swarmer or a \u201c living fossil