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, a remnant of the c segment, 
retained as a kinetosomal grouping that lies in the 
 director meridian , the postoral space between kinety 1 
and kinety n (Coats & Small, 1976). During phi-
lasterine stomatogenesis , kinetosomal proliferation 
occurs in relation to each of these components, pro-
viding kinetosomes for the opisthe oral structures, 
while the parental structures reorganize to form the 
proter oral apparatus (Fig. 15.10). This pattern has 
been observed in Cohnilembus (Didier & Detcheva, 
1974), Dexiotricha (Peck, 1974), Philaster (Coats 
& Small), Potomacus (Ramsey, Brownlee, & Small, 
1980), Mesanophrys (Morado & Small, 1994), 
Uronemella (formerly Uronema filificum ) (Ma, Song, 
& Ma, 2002; Pérez-Uz, Song, & Warren, 1996), 
Paranophrys (Ma, Song, & Hu, 2001), Metanophrys
(Ma & Song, 2003), Pseudocohnilembus (Ma et al., 
2003b), and Uronema (Ma et al., 2004). There is a 
considerable diversity in oral structure morphology 
and patterns of stomatogenesis within the estab-
lished families of philasterines , and this is confirmed 
by diversity in the SSUrRNA gene sequences (Lynn 
& Strüder-Kypke, 2005; Ma et al.). This calls into 
question the taxonomy of the scuticociliates pre-
sented by Lynn and Small (2002). We have, how-
ever, basically retained these familial assignments 
15.5 Division and Morphogenesis 317
until a clearly rationalized alternative arrangement 
is proposed ( see Chapter 17 ). 
 There have been only a handful of recent studies 
on pleuronematine and thigmotrich scuticociliates 
using protargol silver impregnation, the staining 
procedure that best reveals kinetosomal structures. 
Thus, generalizations for these groups cannot easily 
be made. Dolan and Antipa (1985) suggested two 
 stomatogenetic patterns for these non- philasterine 
 scuticociliates : (1) oral primordia derived from the 
paroral and scuticovestige , observed in Ancistrum
(Hatzidimitriou & Berger, 1977), Cyclidium
(Grolière, 1980), and Conchophthirus (Antipa & 
Hatzidimitriou, 1981); and (2) oral primordia 
derived only from the paroral , accompanied by 
considerable dedifferentiation of the parental oral 
apparatus, observed in Histiobalantium (Dragesco 
& Iftode, 1972), Mytilophilus and Peniculistoma
(Dolan & Antipa), and Pleuronema (Grolière & 
Detcheva, 1974; Ma, Gong, & Song, 2003a; Small, 
1967) (Fig. 15.11). Njiné and Ngassam (1993) 
have shown that stomatogenesis in the thigmo-
trich hysterocinetid Ptychostomum begins as a 
 parakinetal kinetosomal proliferation , anterior to 
the parental oral apparatus. While this distances 
the hysterocinetids from other thigmotrichs , we do 
not believe it yet warrants placing them in a sepa-
rate subclass, as suggested by some (de Puytorac, 
1994f; Ngassam & Grain, 2002). It is important to 
remember that position is developmentally “prior” 
to pattern. Thus, we conclude that hysterocinetid 
 stomatogenesis may be one of those instances 
where our interpretation of the underlying morpho-
genetic “pattern” is confused by the surface kineto-
somal structures. We await molecular evidence to 
refute or corroborate their position as thigmotrichs 
within the Subclass Scuticociliatia . 
 The hymenostomes have been reduced to a 
smaller subset of oligohymenophorean families, 
which Foissner (1996b) categorizes as showing 
 parakinetal stomatogenesis . Tetrahymena is the 
archetypical hymenostome , showing monoparaki-
netal stomatogenesis (Fig. 15.11) (Frankel, 1989; 
Grolière, 1975a). The oral primordium typically 
forms at the equator by kinetosomal prolifera-
tion at what is defined as Kinety 1, the “stoma-
togenic kinety” , but which is reported to occur at 
other kineties also (Frankel, 1966, 1989; Nanney, 
1967). This typical hymenostome pattern has 
been observed in Glaucoma (Frankel, 1960; Peck, 
1975), Tetrahymena (Bakowska, Nelsen, & Frankel, 
1982a; Grolière), and Turaniella (Iftode et al., 
1970). The polykinetids assemble through a proc-
ess reminiscent of that described in the spirotrichs 
by Jerka-Dziadosz (1981a). Dikinetids are formed 
that later align to form the two primary rows of 
each oral polykinetid, followed by replication of a 
third and sometimes fourth row (Bakowska et al., 
1982b; Frankel et al., 1984a, 1984b). The gradient 
of differentiation proceeds from the upper left of 
the primordial field to the lower right (Peck, 1974). 
The paroral finally develops along the right border 
of the primordial field by assembly of a ciliated 
file of single kinetosomes that replicate an external 
kinetosome to form the paroral dikinetids . These 
external kinetosomes become ciliated as the inter-
nal kinetosomes lose their cilia (Bakowska et al., 
1982a, 1982b; Nelsen, 1981). What is intriguing is 
the pattern of paroral assembly and disassembly in 
the proter: the external kinetosomal file separates 
from the internal and a new external kinetosome 
is replicated prior to the dedifferentiation of the 
“old” kinetosomes (Bakowska et al., 1982a, 1982b; 
Nelsen, 1981). Bakowska et al. (1982b) make 
the intriguing proposal that this is a phylogenetic 
signal of the common ancestry of hymenostomes 
and scuticociliates , and by extension even to the 
 peniculines – in the hymenostomes , these “old” 
kinetosomes normally dedifferentiate rather than 
remain to participate in the next fission. 
 This archetypical hymenostome pattern is mod-
ified in two circumstances. First, during oral 
replacement , the oral apparatus is dedifferentiated 
and replaced without cell division in microstome 
 hymenostomes when proliferation of kinetosomes 
from the “old” paroral and a region posterior to 
the parental oral apparatus provides the source of 
kinetosomes for the new oral apparatus (Frankel, 
1989; Williams & Frankel, 1973). This pattern 
of stomatogenesis is also characteristic of those 
Tetrahymena species that transform into macros-
tomes , developing the larger oral apparatus by 
a process of replacement similar to that in the 
microstomatous species described above (Buhse, 
1966; Méténier & Grolière, 1979; Njiné, 1972). 
The second modification of this pattern occurs in 
the ophryoglenines whose pattern is characterized 
as teloparakinetal (Foissner, 1996b). In this group, 
adapted for histophagy and parasitism, cell division 
of the encysted tomont is preceded by complete 
dedifferentiation of the parental oral structures. 
Only at the end of the series of palintomic divi-
sions does the oral apparatus differentiate from 
an oral primordium derived by replication at the 
anterior ends of a number of somatic kineties. The 
paroral in Ophryoglena and Ichthyophthirius is 
completely dedifferentiated during the final stages 
of stomatogenesis, a feature these ophryoglenines 
share along with the differentiation of the organelle 
of Lieberkühn (Foissner, 1996b; de Puytorac et al., 
 Division morphogenesis of peritrichs can be 
relatively simple in solitary forms, and can become 
increasingly more complex in colonial forms and 
in symbiotic forms. In colonial forms, such as 
Zoothamnium species, cell division and subse-
quent development can explain the structure of 
the colony itself and the differentiation of several 
types of zooids (Fauré-Fremiet, 1930; Summers, 
1938). In symbiotic epibionts, division and forma-
tion of telotrochs appear to be correlated with the 
 molt cycle of their crustacean hosts (Clamp, 1973; 
Walker, Roberts, & Usher, 1986). Lom (1964) 
provided the modern schema for peritrich stoma-
togenesis by studying protargol impregnations 
of dividing Telotrochidium . A germinal kinety or 
field , adjacent to the parental paroral , proliferates 
to provide kinetosomes for the opisthe’s paro-
ral and oral polykinetids 2 and 3 (Fig. 2–6Ac). 
The parental paroral provides kinetosomes for 
the opisthe’s oral polykinetid