Cap 12

Stomatogenesis in 
Sorogena is of this type, and occurs by prolifera-
tion within and between about six posterior, right 
ventral somatic kineties (Fig. 12.5) (Bardele et al., 
1991). This is followed by a clockwise rotation of 
the field and differentiation of paroral dikinetids on 
the anterior and ultimately right side of the primor-
Fig. 12.5. Division morphogenesis in the Class COLPODEA . A The merotelokinetal stomatogenesis of Colpoda
occurs within a division cyst and begins with complete dedifferentiation of the oral structures ( a , b ). Kinetosomal
proliferation then occurs at the anterior ends of several somatic kineties ( c ) and the right and left oral structures dif-
ferentiate from different subsets of these somatic kineties ( d ) (from Foissner, 1993a). B The pleurotelokinetal pattern 
is more widespread within the class, exemplified here by Sorogena . Kinetosomal proliferation begins on several 
kineties in the posterior right region of the body ( a ). A paroral and oral polykinetids begin to differentiate along the 
anterior and posterior borders of the primordial field, respectively ( b ). As the field rotates clockwise ( c ) and migrates 
anteriorly ( d ), these become the right and left oral structures respectively. (from Bardele et al., 1991.)
dial field and several oral polykinetids on the poste-
rior and ultimately left side of the primoridial field 
(Fig. 12.5). This basic pattern has been observed in 
Platyophrya (Dragesco et al., 1977; Grolière, 1975b) 
and Woodruffia (= Woodruffides ) (de Puytorac 
et al., 1979b; Prelle, 1963). A similar pattern has 
also been reported for Bryometopus (Wirnsberger 
et al., 1985b) and Cyrtolophosis (Díaz, Martín-
González, Borniquel, & Gutiérrez, 2000). 
 There is as yet no study of bryophryid stoma-
togenesis while stomatogenesis of bursariomorphids 
has only been studied once. Perez-Paniagua, de 
Puytorac, and Savoie (1980) demonstrated that 
Bursaria undergoes a pleurotelokinetal stomatogenesis 
by kinetosomal replication within and between a 
number of right posterior somatic kineties. Similar 
to colpodids , the left oral polykinetids are composed 
of dikinetids aligned to make two rows to which a 
third is added to complete stomatogenesis . However, 
these never fuse, as in colpodids , but remain as a 
series of separated adoral polykinetids . The right 
oral structures derive from a more disordered kineto-
somal proliferation that eventually develops into the 
multiple and oblique but parallel files of dikinetids of 
the “paroral” of this ciliate (Foissner, 1996b). 
 12.6 Nuclei, Sexuality 
and Life Cycle 
 Colpodeans typically have a single macronucleus . 
Depending upon cell size , larger colpodeans may 
have many micronuclei (e.g., Colpoda magna , 
Bursaria truncatella ) (Foissner, 1994b). The 
 macronucleus varies from globular to ellipsoid 
in smaller species to an elongate band-shape in 
larger forms (Figs. 12.1, 12.2). The micronucleus 
is globular to ellipsoid. Colpodids especially 
have a prominent nucleolus, which takes a vari-
ety of forms (Burt, Kidder, & Claff, 1941). The 
 nucleolus is actually an aggregation of a number 
of nucleolar organizing regions that assume 
various, often species specific arrangements. 
Although giving the appearance of a heteromer-
ous nucleus, distribution of nucleoli in other 
 colpodeans confirms that the colpodean macro-
nucleus is homomerous (Raikov, 1969). Another 
unusual feature of the colpodean nuclear apparatus 
is the fusion of macronuclear and micronu-
clear envelopes, especially in cyrtolophosidids 
(Detcheva, 1976; Dragesco et al., 1977; Golder, 
1976). This has been used as a defining charac-
ter for the Order Cyrtolophosidida (Foissner, 
1994b; Lynn & Small, 2002; Small & Lynn, 
1985). However, there are now reported excep-
tions within the genus Cyrtolophosis (Díaz et al., 
2000) and in forms related by stomatogenesis, 
such as Bryometopus (Wirnsberger et al., 1985b). 
Thus, we have abandoned this feature as diag-
nostic of the Order Cyrtolophosidida . 
 Division of colpodean macronuclei occurs 
through participation of intramacronuclear micro-
tubules (Kuck & Ruthmann, 1985). Micronuclear 
chromosomes are attached by kinetochores to 
single microtubules that apparently shorten as the 
interpolar microtubules elongate during micro-
nuclear division (Kuck & Ruthmann, 1983). 
 Micronuclei in multimicronucleate species prob-
ably all undergo fission but, due to the large size 
of the cells that they are found in, may not separate 
their products to different poles (e.g., see Beers, 
1946a). Occasional amicronucleate clones may 
arise but they apparently have limited viability 
(Beers, 1946a, 1946b; Piekarski, 1939). The divi-
sion of the macronucleus of small colpodids , like 
Colpoda steinii , involves the formation and separa-
tion of a small number of discrete chromatin aggre-
gates (Burt et al., 1941; Piekarski, 1939; Frenkel, 
1978). This was confirmed by electron microscopy 
in both small and larger species (Frenkel, 1980, 
1982). Quantitation of the DNA in these nuclei led 
to the hypothesis that these were diploid subnuclei 
undergoing separation (Frenkel, 1978; Frenkel, 
Kudryavtsev, & Kudryavtseva, 1973). Although this 
may be the case in colpodeans with low macronu-
clear ploidy, such as Colpoda steinii , it seems less 
likely for colpodeans like Bursaria whose ploidy 
can exceed 5,000 n (Raikov, 1969). In Bursaria , 
composite chromosomes and polynemic structures 
have been observed, suggesting that there is a higher 
order organization to its DNA structure, even if 
it is not organized as diploid subnuclei (Raikov; 
Sergejeva & Bobyleva, 1995). Popenko et al. 
(1998b) demonstrated that the macronuclear DNA 
molecules of Bursaria range from 50–360 kbp, 
probably packed in chromatin aggregates that are 
themselves formed into higher-order structures. 
DNA from Bursaria is about 50% single copy 
sequence with much of the remainder being highly 
repetitive (Borchsenius & Sergejeva, 1979). Other 
12.6 Nuclei, Sexuality and Life Cycle 255
256 12. Subphylum 2. INTRAMACRONUCLEATA: Class 6. COLPODEA
 colpodeans have macronuclear chromosomes that 
range from 90–2,000 kbp and show karyotypic 
variation among species in the chromosome size on 
which rDNA genes reside (Martín et al., 1997). 
 Conjugation has only been described in Bursaria
and has never been reported in any colpodid (Raikov, 
1972). Poljansky (1934) reported conjugation to 
occur in the fall in Bursaria , but the environmental 
cues are not known. Micronuclear meiosis is typical 
and demonstrates a “ parachute stage ” as is commonly 
observed in ciliates. Although many micronuclei 
undergo meiosis , only the one nearest the zone of 
contact and its denser cytoplasm undergoes a third 
division to produce the gametic nuclei . Raikov 
(1972) established a unique subtype for the develop-
ment of macronuclear anlagen and micronuclei in 
Bursaria , which is characterized by the development 
of four macronuclear anlagen and four micronuclei. 
Poljansky and Sergejeva (1981) described oligo-
tenic-like chromosomes during macronuclear anla-
gen development and likened the process to anlagen 
development in spirotrichs and phyllopharyngeans , 
but this observation has yet to be corroborated. 
 Sexual processes are known to “restart” the life 
cycle clock of ciliate populations that are becoming 
 senescent (Sonneborn, 1954; Dini & Nyberg, 1993). 
Under this model, it is remarkable that some lines of 
 colpodids , which never undergo conjugation (e.g., 
Colpoda magna ), show no signs of senescence 
after over 500 generations (Beers, 1944), although 
senescence may begin at double that number of cell 
generations (Crippa Franceschi, Schieti Cavazza, 
& Boccardo Rinesi, 1967). Extrusion bodies have 
been consistently observed during division of the 
macronucleus