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two cortical ridges of the oligohymenophorean Colpidium campylum . Note the longitudinal microtubules ( L ) above 
the epiplasm and the postciliary microtubules ( Pc ) underlying the epiplasm (from Lynn & Didier, 1978). E Freeze-fracture 
replica of the external faces of the inner alveolar membranes of the nassophorean Nassula citrea . Note the cilium ( C ) emerg-
ing between two alveoli , the parasomal sac ( PS ) anterior to the cilium, and in-pocketings of the alveolocysts (arrows) (see 
Fig. 4−10G) (from Eisler & Bardele, 1983). F Cross-section of the somatic dikinetid of the colpodean Colpoda magna . Note 
the single postciliary microtubule (arrow) associated with the anterior kinetosome. G Section through two adjacent alveoli 
(A ) in the cortex of the nassophorean Furgasonia blochmanni . Note that the alveoli extend into the cell in the form of alveo-
locysts ( Ac ). M – mitochondrion (from Eisler & Bardele, 1983). H Cross-section of the somatic monokinetid of the phyl-
lopharyngean Trithigmostoma steini (from Hofmann & Bardele, 1987). I Cross-section of the somatic monokinetid of the 
 oligohymenophorean Colpidium campylum (from Lynn & Didier, 1978). J Cross-section of the somatic monokinetid of the 
 prostomatean Coleps bicuspis . K Cross-section of the somatic kinetid of the litostomatean Lepidotrachelophyllum fornicis
scopy has demonstrated that several silver-staining 
methods are highly specific for these fibrillar com-
ponents (Foissner & Simonsberger, 1975a; Tellez, 
Small, Corliss, & Maugel, 1982; Zagon, 1970). 
Thus, the patterns observed after such staining pro-
cedures are grounded in the cytoskeletal structures 
of the cells, further confirming their essential use-
fulness as tools for systematists . 
 How this 9 + 2 structure evolved is still open to 
speculation. Hartman (1993) imagined its gradual 
evolution from a 3 + 0 structure, still found in some 
parasitic gregarines , like Diplauxis , by additions of 
“nucleating three’s” – from a 6 + 0 to a 9 + 0 structure 
also found in some gregarines , like Stylocephalus
(Kuriyama, Besse, Gèze, Omoto, & Schrével, 2005; 
but see Mitchell, 2004). 
 In addition to the kinetosomal fibrillar associates, 
there is a variety of other fibrous and filamentous 
components in the cortex, which also function to 
maintain or change cell shape (Adoutte & Fleury, 
1996; Allen, 1971; Garreau de Loubresse, Keryer, 
Viguès, & Beisson, 1988; de Haller, 1984a, 1984b; 
Huang & Pitelka, 1973). 
 The somatic cortex is also differentiated in many 
species to provide a means of attachment to the 
substrate. These differentiations range from special 
 thigmotactic cilia to complex attachment struc-
tures, like stalks and hooks (Fauré-Fremiet, 1984). 
Undoubtedly the most complex attachment structure 
exhibited by any ciliate is the attachment disc of 
the mobiline peritrichs , underlain by a complex set 
of fibres and denticles to form a “suction cup-like” 
structure (Fig. 4.6E) (Favard, Carasso, & Fauré-
Fremict, 1963; Hausmann & Hausmann, 1981b). 
 More details on the somatic cortex can be 
found in later chapters and in reviews by Adoutte 
and Fleury (1996), Grain (1984), Lynn (1981), 
Lynn and Corliss (1991), Paulin (1996), and de 
Puytorac (1984a). 
 4.4 Oral Structures 
 The oral region shows great diversity among 
ciliates, a reflection of the ecological diversity 
within the phylum (Figs. 4.3–4.6, 4.12). If we use 
Eisler’s model (Eisler, 1992), we assume that the 
simplest and earliest oral ciliature was a set of 
dikinetids extending along the righthand side of the 
oral region (Fig. 4.2). The oral dikinetids typically 
bear a single postciliary microtubular ribbon 
(Fig. 4.13). These microtubules often extend 
towards the cytopharynx , directing the movement 
of precursor or disc-shaped vesicles to the food 
vacuole -forming region where they fuse with the 
plasma membrane to provide membrane for the 
forming food vacuole (Allen, 1984). A typical 
oral organization has a set of adoral polykinetids 
or membranelles on the lefthand side of the oral 
region (Figs. 4.2, 4.3). These oral polykinetids are 
often initially constructed of dikinetids that assemble 
side-by-side into the organellar complexes to form 
Fig. 4.11. Schematic drawing of the somatic cortex of a ciliate illustrating the interrelationships of the various structures
4.4 Oral Structures 107
108 4. Phylum CILIOPHORA – Conjugating, Ciliated Protists with Nuclear Dualism
two rows to which a third and fourth rows may 
be added by additional kinetosomal replication 
(Fig. 4.14) (Frankel, 1989; Jerka-Dziadosz, 
1981a). The complexity and diversity of these 
 adoral polykinetids has given rise to a prolifera-
tion of terms that help to classify this diversity 
– cirromembranelle , membranelle , membranoid , 
 heteromembranelle , paramembranelle , peniculus , 
 polykinety , and quadrulus (see Chapter 2. 
Glossary for details). Further details of each of 
these structures and references to the primary 
literature are provided in the following chapters 
describing the features of each class. 
 Oral dikinetids are also found in prostomial 
forms (Fig. 4.12). In the Class PROSTOMATEA , 
ultrastructural evidence suggests that these develop 
from a paroral primordium that migrates and encircles
the cytostomial region (Huttenlauch & Bardele, 
1987). However, in the Class LITOSTOMATEA , 
Foissner and Foissner (1985, 1988) have proposed
that the “original” oral ciliature has been lost 
and the oral dikinetids that we now see have 
been derived secondarily from the “oralization” of 
somatic kinetids. This is certainly consistent with 
the orientation of these oral dikinetids, which are 
not rotated and/or inverted like those of the paroral. 
Instead, the transverse or “anterior” microtubular 
ribbons of litostome oral dikinetids extend directly 
to support the cytopharynx (Fig. 4.13). Another 
novel hypothesis has been proposed for the oral 
structures of the Class PHYLLOPHARYNGEA .
Bardele and Kurth (2001) proposed that the ances-
tral phyllopharyngean , now extinct, had also lost 
its primary oral ciliature, and had instead a sucto-
rial oral apparatus , possibly similar to present−day 
 rhynchodines . Therefore, the complex oral ciliature 
of cyrtophorine phyllopharyngeans was derived 
later from “oralization” of somatic kinetids during 
stomatogenesis. This formation of oralized somatic 
kinetosomes in litostomes and phyllopharyngeans 
has been called deuterostomisation (Bardele & 
Kurth, 2001). 
 Acquiring food can be a simple process of 
encountering edible food particles and then ingest-
ing them, a behavior that is typical of prostomial 
forms and those with simpler arrangements of oral 
Fig. 4.12. Schematic drawings illustrating the diversity of kinds of oral regions in the Phylum Ciliophora
ciliature (Fig. 4.12) (Peck, 1985; Tucker, 1968; 
Wessenberg & Antipa, 1970). Ciliates with a paro-
ral and adoral polykinetids are characterized as 
 suspension feeders . The polykinetidal cilia can be 
used to both create the current and filter particles 
out of the suspension – the so-called upstream filter 
feeders – or the current can be created by these cilia 
and the particles filtered by the cilia of the paroral 
– the so-called downstream filter feeders (Fig. 4.15)
(Fenchel, 1980a). Suspension feeding ciliates are 
typically considered to be non-selective feeders, 
“discriminating” among particles primarily on the 
basis of size (Fenchel, 1980b, 1980c). However, 
ciliates with filter-feeding oral apparati do dem-
onstrate some selectivity, so feeding and ingestion 
may be more complicated than a simple mechanical 
process (Sanders, 1988; Stoecker, 1988; Stoecker, 
Gallager, Langdon, & Davis, 1995). 
 Food or food particles are sequestered in a food 
vacuole or phagosome . The food vacuole membrane
is constructed when hundreds