Cap 10

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 “oral” 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 
 “suctorial” 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 “ring” of microtubules, making the 
 hypocomid “suctorial” 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 – Grell & 
Meister, 1982b; Rhyncheta – 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
– 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’s 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 “gluing” 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 “ ten-
tacles ” 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 – is the permanently ciliated Cyathodinium a 
 neotenous suctorian swarmer or a “ living fossil