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Contrary to 
Small and Lynn (1985), the molecular genetic 
evidence now strongly links the peniculines to the 
other oligohymenophoreans (Strüder-Kypke et al., 
2000a, 2000b). Moreover, Beran (1990) has made 
the most recent compelling argument for ontoge-
netic homologies between peniculines and other 
 oligohymenophoreans in his investigations of the 
early development of the oral anlage. Beran (1990) 
considered as homologues the following structures 
involved in oligohymenophorean stomatogenesis : 
the ophryokineties of the peniculine Frontonia , the 
 anarchic field of the peniculine Paramecium , and 
the scutica of the scuticociliates , and this may be 
extended to the germinal row of peritrichs (Figs. 
15.10, 15.11). With this assumption of homology, 
these ontogenetic features corroborate the mono-
phyly of this class. 
 Peniculine stomatogenesis has been charac-
terized as ophryobuccokinetal (Foissner, 1996b). 
While there is no doubt on molecular and morpho-
logical grounds that the frontoniids and parameciids 
are sister taxa, there are differences in their division 
Fig. 15.10. Division morphogenesis of representatives from subclasses of the Class OLIGOHYMENOPHOREA . 
A In the Subclass Peniculia , represented by Frontonia , stomatogenesis is considered ophryobuccokinetal because it 
involves proliferation of kinetosomes from the parental paroral and from several “ophryokineties” to the right of the 
oral region ( a , b ). As stomatogenesis proceeds, a new paroral differentiates on the left of the field for the proter while 
the opisthe’s oral apparatus differentiates into the three peniculi and a paroral as it migrates posteriorly ( c , d ). (from 
Song, 1995.) B In the Subclass Scuticociliatia , Philaster represents the Order Philasterida . Stomatogenesis begins by 
proliferation of kinetosomes from the parental paroral and the scutica , which resides in the director meridian between 
Kineties 1 and n ( a , b ). Kinetosomes from the paroral migrate posteriorly along the right to form the opisthe’s paroral 
and part of the oral polykinetids ( c ). As the proter’s paroral reconstitutes itself ( d , e ), the opisthe’s oral structures take 
shape with the scutica appearing as a “hook-like” attachment at the posterior end of the developing paroral. (from 
Coats & Small, 1976.)
Fig. 15.11. Division morphogenesis of representatives from subclasses of the Class OLIGOHYMENOPHOREA . 
A In the Subclass Scuticociliatia , Pleuronema represents the Order Pleuronematida . A large portion of the parental 
paroral dedifferentiates and kinetosomal replication occurs along this c segment or scutica , categorizing the stoma-
togenesis as scuticobuccokinetal ( a , b ). The oral polykinetids and paroral for the opisthe begin to differentiate as they 
migrate posteriorly, leaving the paroral of the proter to reassemble ( c , d ). Near the final stages, the scutica appears 
as a J-shaped structure at the posterior end of the paroral in each cell ( e ). (From Ma et al., 2003a.) B In the Subclass 
 Hymenostomatia , Tetrahymena is the classic example of parakinetal stomatogenesis . Kinetosomes proliferate along 
the equator of what is defined as Kinety 1 or the stomatogenic kinety ( a , b ). As this proliferation continues, devel-
opment of the oral structures takes place from the anterior towards the posterior and from the right towards the left 
(c–e ) (redrawn after Grolière, 1975a). C In the Subclass Apostomatia , Hyalophysa shows what have been interpreted 
as stomatogenesis during tomite development. Three closely spaced kineties, designated a , b , and c , overly a small 
kinetofragment (* in a ), which develops as the rosette . These three kineties themselves undergo dedifferentiation and 
redifferentiation to produce the kinetal structures of the mature tomite ( b–e ). The homologies with other oligohy-
menophoreans are very difficult to see. (from Bradbury et al., 1997.)
morphogenesis . The oral apparatus of frontoniids 
develops, in some species, by participation of a 
set of special kineties to the right of the oral cav-
ity – the ophryokineties – and in all species, by 
participation of the parental paroral, which serves 
as a site for kinetosomal replication for opisthe 
structures (Fig. 15.10) (Beran, 1990; Song, 1995). 
In parameciids , an anarchic field to the right of the 
paroral serves as the site for replication of kineto-
somes that construct the oral organellar complexes. 
Upon completion of stomatogenesis , a new anar-
chic field differentiates in readiness for the next 
cell division (Jones, 1976). UV-irradiation studies 
suggest that this area of the oral cortex is crucial in 
formation of a functioning oral apparatus (Hanson, 
1962). Parental structures in peniculines may be 
partially or completely reorganized (Fig. 15.10) 
(Foissner; Roque, 1961a; Shi, 1980). Dividing 
Paramecium also assembles longitudinal, supraepi-
plasmic microtubules in the somatic cortical ridges 
(Sundararaman & Hanson, 1976). Fluorescently-
labelled tubulin antibodies have demonstrated that 
these microtubules, collectively termed the cyt-
ospindle , assemble early in cell division correlated 
with the disassembly of other components of 
the cytoskeleton (Cohen, Adoutte, Grandchamp, 
Houdebine, & Beisson, 1982; Delgado, Romero, & 
Torres, 1990; Iftode et al., 1989). Hymenostomes 
and scuticociliates , at least among other oligohy-
menophoreans , have longitudinal, supraepiplasmic 
microtubules throughout the cell cycle. Is this con-
dition in Paramecium a recapitulation of an ances-
tral pre- oligohymenophorean state, since it may also 
occur in dividing nassophoreans (Tucker, 1971b) 
( see Chapter 11 ) or is it a presage for a derived neo-
tenous state, which is exhibited by hymenostomes 
and scuticociliates ? Urocentrum turbo , a ciliate 
whose SSUrRNA gene sequence places it outside 
the peniculine clade (Strüder-Kypke et al., 2000b), 
shows parameciine features in its stomatogenesis 
(Foissner; Martín-González, Serrano, Guinea, & 
Fernández-Galiano, 1986). Thus, until the rDNA 
gene sequence data are corroborated by other 
genes, we maintain Urocentrum as a peniculine . 
 The scuticociliates were recognized as a group by 
Small (1967) who demonstrated homologies in the 
 stomatogenesis of a number of hymenostome -like 
ciliates that he had assigned to his newly conceived 
order Scuticociliatida . During stomatogenesis, the 
paroral or a grouping of kinetosomes associated with 
the posterior end of the paroral – the scuticovestige 
– gives rise to kinetosomes for the opisthe’s oral 
apparatus (Figs. 15.10, 15.11). The scutica itself is 
a transient structure, and often takes the form of a 
“whip-lash” or “J” during philasterine scuticociliate 
 stomatogenesis , hence its name (Fig. 15.10). In some 
cases, kinetosomal involvement in stomatogenesis 
also includes participation of kinetosomes derived 
from the dedifferentiating parental oral polykinetids 
(Dolan & Antipa, 1985; Small). With these two 
features, Foissner (1996b) characterized this type as 
 scuticobuccokinetal . The literature has grown consid-
erably since Small’s review, providing support for at 
least two major stomatogenetic types, correlated with 
the orders in the subclass (Figs. 15.10, 15.11). 
 While there is considerable variability in the 
details of the stomatogenic pattern, Coats and Small 
(1976) proposed a schema in which the paroral plays 
a central role. They viewed it to be composed of an 
anterior or a segment, a middle or b segment, and a 
posterior or c segment. The philasterine scuticocili-
ates have been much more extensively studied than 
representatives from the other orders. The philaster-
ines typically have a paroral with a and b segments, 
and a scuticovestige