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Abstract Ciliates now assigned to the Class 
COLPODEA were scattered throughout the 
phylum in unrelated classes and orders. However, 
it was the structural conservatism of the cortex 
and its somatic kinetids that enabled the iden-
tification of this natural assemblage based on 
cortical ultrastructure, a fact that has been con-
firmed by small subunit rRNA gene sequences. 
Colpodeans are the quintessential cyst-formers 
in the phylum, and are therefore typical in habi-
tats that have a high probability of desiccation: 
mosses, soils, and leaf litter are typical habitats. 
However, colpodeans are found in ponds and 
lakes, although rarely in marine habitats. Their 
prey varies with their cell size: smaller col-
podeans eat bacteria while the largest colpodean 
Bursaria can ingest Paramecium . The somatic 
kinetid is a dikinetid with well-developed over-
lapping transverse microtubular ribbons derived 
from the posterior kinetosome and forming what 
is called the LKm fiber or transversodesma 
– the strong synapomorphy for the group. Oral 
structures range from a paroral that almost 
encircles a prostomatous oral region to a huge 
deep oral cavity, almost spirotrich-like, adorned 
with many oral polykinetids. Stomatogenesis 
ranges from mero- to pleurotelokinetal, and 
in the colpodids typically occurs within a cyst 
 after dedifferentiation of all parental oral 
structures. Conjugation has rarely been observed, 
and it is often assumed that colpodeans are 
completely asexual. This needs to be tested by 
molecular genetic approaches. 
Keywords Palintomy, cryptobiosis 
 The revolution in our view of what morphological 
characters are significant to identifying clades of 
ciliates arose, in part, from investigations of this 
class of ciliates. Lynn (1976a) proposed the struc-
tural conservatism hypothesis based on his study 
of the cortical ultrastructure of colpodeans and a 
comparison of his results with those of the litera-
ture. This conclusion, independently arrived at by 
Gerassimova and Seravin (1976), established, as a 
general rule, the conservative nature of the somatic 
kinetid within clades of ciliates and provided a 
“rule” for establishing phylogenetic affinity. 
 In the Class COLPODEA , several examples illus-
trate the strength of this principle. Ultrastructural 
study of the cortex of Woodruffia by Golder and 
Lynn (1980) confirmed its relationship to colpode-
ans as suggested by Kahl (1930–1935), although 
von Gelei (1954) had originally considered it a 
 heterotrich -like ciliate. Bursaria , for many years 
another “heterotrich” (Corliss, 1979), revealed 
 colpodean -like stomatogenetic features on more 
careful study (Fernández-Galiano, 1979), and its 
 colpodean “nature” was confirmed by ultrastruc-
tural studies (Gerassimova, Sergejeva, & Seravin, 
1979; Lynn, 1980; de Puytorac & Perez-Paniagua, 
1979). McCoy (1974a, 1977) drew attention to 
the colpodean affinities of the stomatogenesis of 
Cyrtolophosis , a genus that had been presumed to be 
a hymenostome (Corliss, 1961), but was confirmed 
to be a colpodean by ultrastructural features of 
the somatic kinetid (Didier, de Puytorac, Wilbert, 
& Detcheva, 1980). As a final example, the unu-
sual sorocarp -forming ciliate, discovered by Olive 
(1978), was named Sorogena (Bradbury & Olive, 
1980) and placed with the haptorians , primarily 
 Chapter 12 
 Subphylum 2.
COLPODEA – Somatically Conserved 
but Orally Diverse 
244 12. Subphylum 2. INTRAMACRONUCLEATA: Class 6. COLPODEA
because of its oral structures. Lynn (1991) sug-
gested that it might be regarded as a colpodean , a 
conclusion confirmed by the study of its ultrastru-
cure and stomatogenesis by Bardele, Foissner, and 
Blanton (1991). Thus, as beautifully illustrated by 
Foissner (1985b) (see Fig. 1.4), colpodean oral 
structures show such broad diversity that the class 
has really only received broad recognition in the 
past 20 years. 
 Colpodean ciliates are extremely common, 
especially in terrestrial habitats where the genus 
Colpoda is almost ubiquitous. Colpodeans range 
in size from about 10 µm in length for the genus 
Nivaliella to over 500 µm in length for Bursaria 
truncatella , an almost 200,000 times difference 
in cell volume (Foissner, 1993a). Colpodeans are 
generally holotrichously ciliated. The kineties are 
typically bipolar with a number of them ending on 
the perimeter of the oral region or coursing anteri-
orly to abut in a prominent anterior suture or keel in 
some Colpoda species. The body undergoes torsion 
to varying degrees, a feature that Stout (1960a) 
used to imagine a phylogeny for the group based on 
 D’Arcy Thompson’s Cartesian coordinate analysis. 
This torsion can be lost during cell division as was 
illustrated years ago by Tuffrau (1952). 
 Colpodeans have interested physiologists with 
their life cycle that typically includes a resist-
ant stage or cyst . Early on, Burt (1940) carefully 
described species so physiologists would not misi-
dentify forms. More recently, multivariate statistical 
approaches have been used to discriminate among 
 morphospecies (Foissner & Schubert, 1983; Lynn 
& Malcolm, 1983). Colpoda species have now been 
grown in chemostat cultures on a variety of bacte-
rial species, including Escherichia coli (Drake & 
Tsuchiya, 1977). Undoubtedly the most intriguing 
recent examples of bizarre feeding strategies among 
ciliates have been the discovery of the mycopha-
gous colpodeans in the Family Grossglockneriidae . 
Originally discovered by Foissner (1980d) in the 
 European Alps , they have been described world-
wide as predators of fungi , using their minute 
feeding tube to perforate the cell wall of fungi and 
remove the contents (e.g., Foissner, 1993a, 1999b; 
Foissner & Didier, 1983), and they have now been 
identified from fossilized amber dating from the 
 Lower Cretaceous (Ascaso et al., 2005). 
 De Puytorac et al. (1974b) elevated the colpode-
ans to ordinal rank within the Subclass Vestibulifera .
Small and Lynn (1981) elevated the group to class 
rank based on the structure of the somatic dikinetids , 
which really provide the only synapomorphy for the 
class. The special feature of the colpodean somatic 
dikinetid is the presence of a posteriorly-directed 
transverse ribbon of microtubules associated with 
the posterior kinetosome. These ribbons can extend 
for some distance posteriorly, overlapping each 
other in what has been called the LKm fibre (Golder, 
1974; Golder & Lynn, 1980) or the transversodesma 
(Small & Lynn, 1985). The class name is derived 
from Colpoda , one of the most common genera of 
ciliates, and its name, in turn, is derived from the 
Greek kolpos , meaning breast, referring to the bulging 
shape of some Colpoda species. 
 12.1 Taxonomic Structure 
 As noted above, de Puytorac et al. (1974b) were 
the first to elevate the colpodids to ordinal rank 
within their Subclass Vestibulifera , a position that 
was maintained by Corliss (1979). Small and Lynn 
(1981, 1985) elevated the group to class rank, 
establishing the Class COLPODEA , based prima-
rily on the structure of the somatic kinetid. This 
distinctness as a class, which has been maintained 
by Lynn and Small (1997, 2002), is supported 
both by phylogenetic analyses based on morpho-
logical features (de Puytorac, Grain, Legendre, & 
Devaux, 1984; de Puytorac, Grain, & Legendre, 
1994) and by small subunit (SSU) rRNA gene 
sequences (Lynn, Wright, Schlegel, & Foissner, 
1999). However, one recent molecular study sug-
gests that the colpodeans may be paraphyletic 
(Lasek-Nesselquist & Katz, 2001). 
 The colpodeans have been related to the litostomes
and the nassophoreans based on kinetid structures 
(Aescht, Foissner, & Mulisch, 1991). Phylogenetic 
trees derived from SSUrRNA gene sequences 
support an affinity with prostomateans (Lynn 
et al., 1999) or nassophoreans (Lasek-Nesselquist