Cap 9

which appears 
either as isolated granules in vesibuliferid endo-
plasm or as skeletal plates in the entodiniomor-
phids (Grain, 1994; Nakai & Imai, 1989; Wakita 
& Hoshino, 1980). Starch-like storage products 
have also been observed in the macropodiniids 
(Cameron & O’Donoghue, 2002a, 2003a). 
 Contractile vauoles are a typical feature of the 
 litostomes with some endosymbionts having up 
to 20. The cytoproct is a typical feature of tri-
chostomes , but often not reported in haptorians . 
 Entodiniomorphids have a distinct cytoproct sur-
rounded by a conspicuous filamentous sphincter. 
 9.4 Oral Structures 
 The litostome oral region in its simplest state is on 
the cell surface at the anterior end of the body as in 
 haptorids and archistomatines (i.e., buetschliids ). 
The cytostome is on a dome-like elevation sur-
rounded by circumoral cilia , which are slightly 
longer than the adjacent somatic cilia. In pleu-
rostome haptorians , the oral region has become 
slit-like, extending along the ventral edge of the 
laterally flattened body. In vestibuliferids , blepha-
rocorythids , and entodiniomorphids , the oral region 
has become invaginated to varying degrees and the 
oral ciliature can become functionally differenti-
ated, although still arising essentially from the 
anterior ends of somatic kineties. Prior to electron 
microscopy, the “membranelle-like” behavior of 
the oral cilia of entodiniomorphids suggested that 
they actually had an adoral zone of membranelles 
(Corliss, 1961). This functionality has now been 
redescribed by scanning electron microscopy of 
Entodinium and Cycloposthium (Imai & Yamazaki, 
1988; Imai, Tashiro, & Ishii, 1983). However, there 
is no corresponding structural subdivision at the 
level of the kinetosomes where a “membranellar” 
ultrastructure as in the spirotrichs might be expected 
(Furness & Butler, 1983, 1985). 
 At the ultrastructural level, the circumoral 
kinetids of haptorians are typically dikinetids 
characterized as follows: a ciliated posterior or 
right kinetosome with a postciliary ribbon and 
sometimes a transverse ribbon; and a non-ciliated 
anterior or left kinetosome that bears a tangential 
transverse ribbon, sometimes a single postciliary 
9.4 Oral Structures 203
204 9. Subphylum 2. INTRAMACRONUCLEATA: Class 3. LITOSTOMATEA
microtubule, and a nematodesma (see Grain, 1994; 
Lynn, 1991). These oral dikinetids are often linked 
up by a filamentous annulus that is continuous 
with the filaments of the ecto-endoplasmic layer . 
The transverse ribbons of the anterior kinetosomes 
extend anteriorly and then bend posteriorly to 
support the cytopharnynx. The nematodesmata 
extend posteriorly to form the rhabdos or litostome 
 cytopharyngeal apparatus . Dileptus species may 
have two rings of nematodesmata, the inner one of 
which is not associated with kinetosomes (Grain 
& Golińska, 1969). A set of bulge microtubules 
may be found interior to the nematodesmata and 
extending as a “pallisade” deep into the cytoplasm 
surrounding the cytopharynx from the point where 
the transverse ribbons bend interiorly (Foissner 
& Foissner, 1988; Grain; Kuhlmann, Patterson, 
& Hausmann, 1980; Lipscomb & Riordan, 1991; 
Lynn, 1991). The oral dikinetids can be rotated 
in some haptorians (e.g., Didinium – Lipscomb 
& Riordan, 1992; Foissner & Foissner, 1988) so 
that it may be preferable to refer to right and left 
kinetosomes rather than anterior and posterior ones 
(Grain, 1994). Finally, the slit-like oral region of 
 pleurostomes is also bordered by oral dikinetids 
whose transverse ribbons are also associated with 
 bulge microtubules (Foissner & Leipe, 1995). 
Oral monokinetids are only found in some hap-
torians (Foissner & Foissner, 1985). Lipscomb 
and Riordan (1990) used a parsimony analysis 
and cladistics to conclude that the haptorian oral 
monokinetids are homologous to the anterior or left 
kinetosome of the oral dikinetid (i.e., the posterior 
right kinetosome has not differentiated). 
 The trichostomes have what are termed “oral-
ized” somatic kinetids since Lipscomb and Riordan 
(1990) concluded that these ciliates have completely 
lost the oral dikinetid . This is correlated with the 
loss of toxicysts in these ciliates. Transverse ribbons 
of several of the more anterior oral monokinetids 
of trichostomes may still extend to support the cyto-
pharynx, while nematodesmata and bulge micro-
tubules support the oral cavity or vestibulum and 
cytopharynx of some of these ciliates (Grain, 1994; 
Lynn, 1991). Typically, these “oralized” kineto-
somes have kinetodesmal fibrils that are consider-
ably reduced or absent (Grain, 1966a, 1994; Grim, 
1993a; Guinea et al., 1992; Paul et al., 1989). 
 Feeding and ingestion by litostomes involves 
intimate contact with their prey since they are not 
suspension or filter-feeding ciliates. Clavate cilia 
may be involved in sensing prey or prey metabo-
lites, while the girdle ciliature of the planktonic 
 cyclotrichiids may detect prey by hydromechanical 
signals (Jakobsen et al., 2006). In the rumen ciliate 
Ophryscolex , the paralabial organelle is situated 
on the ventral side of the body adjacent to the oral 
region. This organelle, which has clavate cilia arising 
from files of dikinetids that border a central kinety 
of monokinetids, has been implicated as a sensory 
structure involved in feeding (Bretschneider, 1962; 
Schrenk & Bardele, 1987). Treatment of Dileptus
with proteolytic enzymes has demonstrated that sur-
face proteins are essential for ingestion, while inges-
tion itself is a calcium-dependant process (Estève, 
1984b). Toxicysts are crucial to prey capture 
in haptorians and their discharge is also calcium-
dependant (Iwadate, Katoh, Kikuyama, & Asai, 
1999). Microtubules are also essential to the ingestive 
process as the anti-microtubule drug, colchi-
cine , decreases food vacuole formation in Dileptus
(Tołłoczko, 1980). The food vacuole is formed by 
the fusion of vesicles with the plasma membrane of 
the cytostome (Kuhlmann & Hausmann, 1983). The 
digestive process is similar to that in Paramecium
(see Chapter 15 ) with the fusion of acid vesicles 
with the food vacuole membrane during the initial 
stages of digestion in Litonotus (Verni & Gualtieri, 
1997). In the entodiniomorphids , the complexity 
of the cytopharyngeal apparatus is directly related 
to the diet of the ciliates: species that ingest large 
 plant fragments have larger and more fibrous oral 
structures than those that ingest bacteria and starch 
grains (Furness & Butler, 1988). 
 Extrusomes with toxic capacities are typical of 
 haptorians but have apparently been lost by trichos-
tomes , possibly coincident with the loss of oral dik-
inetids . Several categories of toxicysts have been 
described and the number and their types are char-
acteristic of certain genera. Toxicysts can be both 
proteolytic and paralytic. Didinium typically has 
three types: (1) the longer toxicysts that extend out 
tube-like to paralyze prey and begin proteolysis of 
the prey; (2) cyrtocysts that may be prototype toxi-
cysts; and (3) pexicysts that are shorter and appear 
to fasten the predator to its prey (Hausmann, 1978; 
Wessenberg & Antipa, 1969, 1970). Homalozoon
also has both long and short toxicysts . Even shorter 
 extrusomes , called conocysts , are trichocyst-like in 
that their contents are rod-like, bearing a pin-like 
element at the tip when extruded (Hausmann, 1977; 
Kuhlmann & Hausmann, 1980). Toxicysts develop 
in the endoplasm and are probably assembled by 
the endoplasmic reticulum through the classical 
cellular secretory pathway (Dragesco, Auderset, 
& Baumann, 1965; Hausmann, 1978). 
 Finally, brief mention must be made of what 
we know about the regulation of oral structures 
in litostomes . Kink (1976) demonstrated a zone 
of kinetosome proliferation near