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1992); the hymenos-
tomes Colpidium , Glaucoma , Tetrahymena , and 
Turaniella (Iftode et al., 1984; Lynn & Didier, 
1978; Nilsson, 1976; Peck, 1978; Williams & 
Bakowska, 1982); and the peritrichs Termitophrya , 
Trichodina , and Thuricola (Eperon & Grain, 1983; 
Maslin-Leny & Bohatier, 1984; Noirot-Timothée 
& Lom, 1965). In turaniellid hymenostomes , paro-
ral kinetosomes may not be ciliated, along only 
part of or the whole length of the paroral (Iftode 
et al., 1984; Lynn & Didier, 1978). 
 For some time, it was conjectured that the oral 
rib microtubules arose from the postciliary microtubules
of the paroral dikinetids . If so, these microtubules must
break during stomatogenesis, because there is firm 
evidence now that the oral rib microtubules arise 
in dense material, often taking the form of a spur 
or papilla, which may extend over top of the non-
ciliated kinetosomes of the paroral (Hausmann 
& Hausmann, 1981; Iftode et al., 1984; Lynn & 
Didier, 1978). This origin is reminiscent of the 
origin of the cytopharyngeal microtubules of the 
 prostomes , such as Coleps (Lynn, 1985). The oral 
ribs are separated by alveoli and are typically 
supported by microtubules arranged as 4 + 2 in 
 hymenostomes and scuticociliates (Lynn & Didier, 
1978; Nilsson, 1976; Peck, 1978; de Puytorac 
et al., 1974a; Sattler & Staehelin, 1979), and 
3 + 1, 3 + 2, and 4 + 2 in peritrichs (Hausmann 
& Hausmann; McKanna, 1973b). 
 Bradbury (1989) finally clinched the phylogenetic 
affinities of the apostomes by discovering a paroral 
during the development of the free- swimming 
 tomite of Hyalophysa . Molecular genetic evidence 
now supports this conclusion (J.C. Clamp 
et al., 2008; Lynn, Strüder-Kypke, & Bradbury, 
2005). The apostomes show a bewilderingly bizarre 
set of cortical kinetosomal assemblages, and all 
have had various authors suggest that they are 
homologues of the oral structures of other ciliates. 
The rosette , although not always present, can also 
clinch membership of a ciliate to this subclass of 
 oligohymenophoreans . The rosette is a tube-like 
invagination, lined by ridges or septa that are cov-
ered by cortical alveoli and provided with some 
cilia and an aggregation of dense vesicles. Its func-
tion is not known, but its ultrastructure has been 
described in typical apostomes like Hyalophysa
(Bradbury, 1966b) and atypical ones like Collinia
(de Puytorac & Grain, 1975) and Conidophrys
(Bradbury & Tyson, 1982). The x , y , and z kineties 
of foettingeriid apostomes have been characterized 
as perioral (Bradbury, 1966a) or as oral (Lynn & 
Small, 2002). Given that kinetodesmal fibrils are 
associated with the kinetosomes of the falciform 
kinetosomal fields of apostomes (Bradbury, 1966b, 
1989; de Puytorac & Grain, 1975), it is more likely 
that these are highly modified arrays of somatic 
kinetosomes. Apostomes feed on the exuvial flu-
ids of the moulted exoskeleton of their crustacean 
host (Bradbury, 1973, 1975b), on the blood of their 
 crustacean host (de Puytorac & Grain), by dis-
solving the host’s exoskeleton (Bradbury, 1975b; 
Bradbury & Goyal, 1976; Bradbury, Deroux, & 
Campillo, 1987), and by penetrating setae on the 
 crustacean exoskeleton to presumably feed on tis-
sue fluid (Fig. 15.2) (Bradbury & Tyson, 1982). 
The ingestatory region in exuviotrophic forms 
extends between somatic kinety 1 and the x , y , and 
z kineties. Food may be ingested via a cytophar-
ynx lined with microtubular ribbons and to which 
diskoidal vesicles are directed for phagosome for-
mation, reminiscent of other ciliates (Bradbury, 
1973, 1975b; Bradbury et al., 1987). Deviants 
from this typical pattern occur in Terebrospira , 
which ingests the solubilized components of the 
exoskeleton by pinocytosis over its entire cell sur-
face (Bradbury, 1975b; Bradbury & Goyal, 1976) 
and by Conidophrys , which ingests, presumably 
setal tissue fluids , through a broad cytostome char-
acterized by delicate tubules (Bradbury & Tyson, 
1982). Digestive enzymes, such as phosphatases , 
15.4 Oral Structures 313
may be secreted outside the cell in some apostomes 
(Bradbury & Goyal, 1976). Phagosomes are acidi-
fied during the digestive process and lysosomes are 
likely involved (Bradbury & Goyal, 1976; Landers, 
Treadaway, Johnson, & Luckie, 2001). 
 In comparison to the above, we are essentially 
ignorant about the feeding biology of the astomes . 
A reasonable conjecture is that they may feed 
like the astomatous mutants of Tetrahymena and 
 apostomes , presumably by pinocytosis via the 
 parasomal sacs , but in the case of the astomes , over 
the entire cell surface (Nilsson & Van Deurs, 1983; 
Rasmussen & Orias, 1975). 
 15.5 Division and Morphogenesis 
 Division by oligohymenophoreans is typically as 
free-swimming cells, which divide equally or isot-
omically. In rare cases, division in peritrichs , thig-
motrichs , and some astomes can be anisotomic or 
unequal. Multiple division, catenulation , or linear 
 palintomy can occur in which chains of cells are 
formed in apostomes , like Polyspira , and astomes , 
like Hoplitophyra and Radiophrya (Fig. 15.5) (de 
Puytorac, 1994g, 1994h). The isolation of cell divi-
sion arrest mutants in Tetrahymena suggests that 
 chain formation may require a modification of per-
haps only one gene product (Frankel, 1989; Frankel, 
Nelsen, & Jenkins, 1977). Palintomy can also occur 
in a reproductive cyst : the tomont stages of the 
 ophryoglenines Ophryoglena and Ichthyophthirius
divide within a reproductive cyst , the latter yielding 
over 4,000 tomites; and the apostome tomonts and 
in some special cases, like T. vorax and Porpostoma , 
divide within a cyst (Fig. 15.1). 
 Foissner (1996b) remarked that the oligohy-
menophoreans include “the pets of the ciliatolo-
gists” – the genera Paramecium and Tetrahymena . 
Species in these two genera have provided models 
for advancing our understanding at two cellular 
levels: (1) the replication of organelles and organel-
lar complexes; and (2) the replication of the pattern 
of the entire cell. This developmental biological 
literature has been extensively treated by Frankel 
(1989), who provides a thorough review of the 
literature and a thoughtful treatment of a variety 
of issues. As we have noted previously, we still have 
much to learn about the cellular and molecular proc-
esses underlying division morphogenesis . Much of 
the systematic literature attributes a particular role 
to a particular kinetosomal structure, and yet there 
are unambiguous refutations of this role attribution. 
For example, somatic kinety 1 of Tetrahymena is 
the rightmost postoral kinety, and it has been called 
the “stomatogenic kinety” because the oral primor-
dium typically develops in association with it (Fig. 
15.11). However, Nanney (1967) demonstrated that 
the primordium can develop along other kineties, 
a phenomenon that he called “cortical slippage” . 
If there were a consistent directional bias in this 
process, ultimately every somatic kinety would 
become a stomatogenic kinety . The inevitable con-
clusion is that the relative position on the somatic 
cortex is the important causal determinant and not
an association with a particular kinety or kineto-
somal structure (Frankel, 1989; Nanney, 1967). It 
is worth remembering this important point in the 
subsequent discussion. 
 Our reference to the literature on developmen-
tal biology will be very selective, highlighting a 
few papers that have relevance to the systemat-
ics. From this perspective, Foissner (1996b) has 
thoroughly reviewed the systematic literature on 
 ontogenesis of oligohymenophoreans . Our cita-
tions to this literature prior to Foissner will mainly 
highlight some exemplary studies as we proceed 
below to characterize each subclass.