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forests (Schnittler, 
Unterseher, & Tesmer, 2006). Sorogena is a preda-
tor of smaller colpodeans . Under an alternating 
photoperiod of light and dark and when prey abun-
dance declines, Sorogena trophonts aggregate as a 
 sorogen on plant fragments or other floating films 
or objects, typically just before sunrise (Sugimoto 
& Endoh, 2006). The sorogen secretes a stalk, elevating 
the secreting cells above the attachment point. 
These cells then encyst as sorocysts , which are 
discharged for dispersal as the sorus dries (Olive & 
Blanton, 1980). Secretory vesicles, probably homo-
logues of the mucocysts of other colpodeans, are 
manufactured in the rough endoplasmic reticulum 
and their contents released by exocytosis during 
stalk formation (Blanton & Olive, 1983a). The stalk 
material expands to a hydrated, fibrillar matrix, 
pushing the sorogen upwards. The stalk material 
then solidifies to provide structural support for the 
 sorus (Blanton & Olive, 1983b). Like the cyst wall 
materials of other colpodeans , the stalk is composed 
of polysaccharides , which probably include glucose 
and N -acetyl- d -glucosamine residues, and proteins, 
which have glycine as a predominant amino acid 
(Blanton, Warner, & Olive, 1983). 
 12.3 Somatic Structures 
 As noted above, colpodeans range in size from the 
very small Nivaliella to the almost macroscopic 
Bursaria . Somatic kineties of colpodeans are bipolar
with a significant number terminating on the oral 
region, especially in species whose oral apparatus 
is at the anterior apex. The colpodean body can be 
slightly twisted, spiralling to the left in forms like 
Platyophrya and this twisting can become extreme 
in colpodids (Figs. 12.1, 12.2). Somatic ciliation 
can be characterized as holotrichous, although in 
smaller colpodids some regions of the cortex can 
have very reduced somatic ciliation (Fig. 12.1). 
 The cell surface of colpodeans is covered by the 
 plasma membrane , which rarely demonstrates ele-
ments of a superficial glycocalyx (Bardele et al., 1991; 
Bradbury & Olive, 1980). The plasma membrane is 
underlain by conspicuous cortical alveoli (Golder 
& Lynn, 1980; Lynn, 1976a, 1977a, 1980). Fauré-
Fremiet and André (1965a) reported an abundance 
of dense granules filling this space in Colpoda
(formerly Tillina ) praestans . The junctions and 
boundaries between these alveoli may give rise to 
the complicated silverline system or argyrome of 
these ciliates, although this is not always the case 
(Foissner, 1981b; Foissner & Foissner, 1994). As 
in other ciliates, the alveoli are underlain by an 
 epiplasmic layer whose thickness appears to be 
correlated with the cell size of the ciliate, at least 
within the colpodids (Lynn, 1977a). Bursaria does 
not have a thick epiplasm , but like the larger colpodids , 
its somatic kinetids give rise to microtubular nema-
todesmata that insert upon a cortical microfilamentous
network, which presumably supports the form of 
these larger cells (Lynn, 1977a, 1980). 
 Of all classes of ciliates, the somatic kinetids 
of colpodeans have caused considerable interest. 
Golder (1974) was the first to report in Woodruffia
the complex overlapping microtubular ribbons, 
called LKm fibers , that extend along the left side 
of the somatic kineties. Lynn (1975) demonstrated 
that Woodruffia also had a typical, striated kine-
todesmal fibril and thus was not an exception to 
the rule of desmodexy as applied to ciliates by 
Chatton and Lwoff (1935b). A few years later, 
several simultaneous reports demonstrated that 
the LKm microtubular ribbons derived from the 
transverse ribbon of the posterior kinetosome of 
the somatic dikinetids (Gerassimova, 1976; Lynn, 
1976a). The colpodean somatic dikinetid is rotated 
about 10–20° clockwise to the kinety axis, viewed 
from outside the cell. The posterior ciliated kineto-
some bears the following: a divergent postciliary 
ribbon that sometimes extends far enough to 
overlap those of more posterior kinetids; a short, 
laterally-directed kinetodesmal fibril that origi-
nates near triplets 5, 6, flattening to a fan-shape 
as it extends upwards in the cortical ridge; and a 
very well developed, tangentially-oriented trans-
verse ribbon that originates from a medial desmose 
connecting the two kinetosomes and extends from 
triplets 3–5 posteriorly and often overlaps several 
other ribbons from more posterior kinetids (Figs. 
12.3, 12.4). The anterior ciliated kinetosome bears 
the following: a single to occasionally several post-
ciliary microtubules and a large tangentially-oriented
Fig. 12.1. Stylized drawings of representative genera from the orders in the Class COLPODEA . The colpodids
Colpoda and Grossglockneria . The sorogenid Sorogena . The cyrtolophosidid Cyrtolophosis . The bursariomorphid 
Bursaria . Inset is a detail of the adoral polykinetids and adjacent somatic kineties
12.3 Somatic Structures 249
Fig. 12.2. Stylized drawings of representative genera from the orders in the Class COLPODEA . The bryometopid
Bryometopus . The bryophryid Bryophrya . The cyrtolophosidids Cyrtolophosis and Woodruffides
Fig. 12.3. Schematics of the somatic dikinetids of the Class COLPODEA . ( a ) The bryophryid Bryophrya . ( b ) The col-
podid Colpoda . ( c ) The cyrtolophosidid Cyrtolophosis . ( d ) The bursariomorphid Bursaria (from Lynn, 1981, 1991) 
transverse ribbon that arises near triplets 3–5 and 
extends laterally into the ridge to overlap the 
compound bundle of posterior kinetosomal trans-
verse ribbons. There may be up to four parasomal 
sacs , two on each side of the kinetid (Fig. 12.3). 
Nematodesmata may also originate from the base 
of one or both kinetosomes (Lynn, 1981, 1991). 
More recent descriptions of colpodean kinetids 
have confirmed this structural pattern for the class 
(Aescht et al., 1991; Bardele et al., 1991; Foissner 
& Foissner, 1994; Platt & Hausmann, 1993). 
Like some oligohymenophoreans (Antipa, 1972), 
the cortex of colpodids can undergo structural 
differentiation . Larger colpodids have a somatic
groove that forms the “hilum” in the kidney-
bean shape. This somatic groove is supported 
longitudinally by strongly overlapping posterior 
transverse ribbons and underlain by orthogonally 
disposed nematodesmata that arise from the bases 
of the groove somatic dikinetids (Lynn, 1976c; 
Lynn & Zimmerman, 1981). The groove can be 
divided into an incurrent and excurrent compo-
nent, which facilitates feeding in Colpoda species 
(Fenchel, 1980a; Lynn, 1976c, 1977a). The larger 
the Colpoda species, the greater the development 
of its somatic groove (Lynn, 1978). 
 Colpodeans typically have at least one contractile 
vacuole , located in the posterior end. Depending 
upon the species, they can be identified as showing 
Type A or Type B morphology (Patterson, 1980). 
Larger cells may have either multiple vacuoles 
(e.g., Bursaria , Foissner, 1993a) or may have long 
 collecting canals radiating anteriorly in the cell’s 
cortex (e.g., Colpoda magna (formerly Tillina 
magna , Tillina canalifera ), Lynn, 1977a; Turner, 
1937). As cell size increases in Colpoda species, 
the relative size of the contractile vacuole and its 
pore increases as does the output of the contracile 
vacuole itself (Lynn, 1977a, 1982). 
 Colpodeans have ovoid to rod-shaped mucocysts . 
These are particularly conspicuous in medium to 
large cells (Foissner, 1993a; Lynn, 1976c, 1977a), 
12.3 Somatic Structures 251
252 12. Subphylum 2. INTRAMACRONUCLEATA: Class 6. COLPODEA
but inconspicuous in smaller ones (Foissner, 1993a; 
Lynn, 1976a, 1976b). The matrix is granular (Lynn, 
1977a) or often completely removed upon fixation 
(Delmonte Corrado, Chessa, & Pelli, 1996; Lynn, 
1976c). The characteristic periodic substructure of 
 mucocysts (Hausmann, 1978) is rarely observed 
(see Perez-Paniagua, Perez-Silva, & de Puytorac,