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habitats (e.g., Halteria , Meseres ). 
Furthermore, there are ecologically significant 
differences in growth rates and responses to tem-
perature between geographically distant isolates 
of species of Uronema (Pérez-Uz, 1995) and 
Urotricha (Weisse & Montagnes, 1998; Weisse 
et al., 2001), and even among clones of planktonic 
Coleps and Rimostrombidium species (Weisse & 
Rammer, 2006). Dini and Nyberg (1999) have 
shown that ecological differentiation of genotypes 
occurs at all levels among species of Euplotes – at 
4.2 Life History and Ecology 103
104 4. Phylum CILIOPHORA – Conjugating, Ciliated Protists with Nuclear Dualism
the morphospecies level, breeding system level, 
 breeding group level, and stock level. Thus, we 
must put pragmatism aside if we are to advance 
our understanding of the interactions between 
the ecological factors and the evolutionary forces 
 shaping ciliate diversity , and we must also move 
beyond the concept of morphospecies. A major 
first step would be to consider models for specia-
tion other than the allopatric one, which is clearly 
inappropriate in its classical interpretation. 
 4.3 Somatic Structures 
 The surface of ciliates is covered by a plasma 
membrane underlain by cortical alveoli (Figs. 4.9B, 
4.10A, 4.10B). In some nassophoreans, the alveoli 
can extend into the cortex as the so-called alveolo-
cysts (Fig. 4.10G). The plasma membrane is char-
acterized by a variety of intramembranous particles 
(Allen, 1978; Bardele, 1983; Hufnagel, 1992). The 
surface membranes are sites of ion channels that 
enable ciliates to sense mechanical, chemical, and 
temperature stimuli (Machemer & Teunis, 1996). 
The alveoli can be the sites of Ca 2+ ion storage 
in some ciliates, thus playing a role in modulat-
ing locomotion (Mohamed et al., 2003; Plattner, 
Diehl, Husser, & Hentschel, 2006; Stelly, Halpern, 
Nicolas, Fragu, & Adoutte, 1995). All these inputs 
to the cell are “translated” into complex behavioral 
sequences that Ricci (1990, 1996) has described 
as an ethogram – a quantitative description of the 
behavioral repertoire of a species. 
 At various points on the cell surface, typically 
associated with the emergence of cilia, parasomal
sacs or coated pits extend into the cytoplasm (Fig. 
4.10E). These sacs can be the sites of pinocytosis 
(Nilsson & Van Deurs, 1983). The membranous 
junctions of neighboring alveoli or fibrous compo-
nents associated with these boundaries (Fig. 4.10E) 
form characteristic patterned networks that are 
revealed upon silver-staining – the so-called argy-
rome (Foissner & Simonsberger, 1975a, 1975b). 
Underlying the alveoli is a fibrous or filamentous 
layer called the epiplasm , which is constructed, 
in part, by specific proteins called epiplasmins 
and articulins (Figs. 4.9B, 4.9C, 4.10B) (Coffe, 
Le Caer, Lima, & Adoutte, 1996; Huttenlauch & 
Stick, 2003; Huttenlauch, Peck, Plessmann, Weber, 
& Stick, 1998b; de Puytorac, 1984a). Genetic 
interference with some of these “cortical” genes 
can influence cell shape (Williams, 2004). 
 The most prominent features of the somatic 
surface of the vast majority of ciliates are the cilia . 
Membranous particles are also distributed in cili-
ary membranes, and undoubtedly function in the 
movement of Ca 2+ ions influencing the ciliary beat 
pattern (Machemer & Teunis, 1996; Plattner, 1975; 
Plattner et al., 2006), and these patterns of intram-
embranous particles on the cilia may characterize 
different groups of ciliates (Bardele, 1981). The 
cilia beat with a straight effective stroke and a 
curved recovery stroke, typically moving the cili-
ate through the medium, whether it be the water of 
an ocean or pond or the digestive contents of the 
intestine of a sea urchin (Sleigh & Barlow, 1982). 
The often thousands of cilia on the cell surface 
are coordinated by a hydrodynamic coupling that 
is manifested in the metachronal waves observed 
passing along the cell’s surface (Guirao & Joanny, 
2007; Sleigh, 1984, 1989). 
 The ciliary axoneme with its 9 + 2 arrangement 
of microtubules underlies the ciliary membrane. 
The major force for the ciliary beat derives from 
active sliding of the nine peripheral doublet micro-
tubules driven by dynein motors and ATP (Satir & 
Barkalow, 1996). The central pair of microtubules 
may rotate in a counterclockwise direction, viewed 
from the outside of the cell, making a complete 
rotation with every beat cycle (Omoto & Kung, 
1980). Furthermore, this defined directional rota-
tion, if true, means that when a patch of cortex is 
rotated, as sometimes happens following conjuga-
tion of Paramecium when the two cells separate, 
the cilia on the reversed patch beat in the opposite 
direction to the surrounding cortex that has a normal 
polarity (Tamm, Sonneborn, & Dippell, 1975). The 
central-pair microtubules are anchored in the axo-
some , which lies in a region of extreme complexity 
– the transition zone – between the ciliary axoneme 
and the basal body or kinetosome (Dute & Kung, 
1978). In reviews, Fokin (1994, 1995) has demon-
strated a considerable diversity in transition zone 
structures in ciliates, and suggested that transition-
zone types may characterize some of the major 
clades of ciliates. 
 The axonemal microtubules arise out of the 
 kinetosome , which is composed in most ciliates of 
nine sets of microtubular triplets. Associated with 
the ciliate kinetosome are three fibrillar associates 
– the striated kinetodesmal fibril , the transverse 
microtubular ribbon , and the postciliary microtubu-
lar ribbon (Fig. 4.10C, 4.10F, 4.10H–K). All these 
elements together – cilium, kinetosome, fibrillar 
associates – form the kinetid . Theoretical calcula-
tions support the notion that these fibrous struc-
tures function as anchors for the kinetid (Sleigh 
& Silvester, 1983). These fibrillar systems have 
 diversified in form and pattern as ciliate lineages 
have evolved, providing a variety of patterns that 
have proved useful in characterizing major clades 
(Fig. 4.7; see Taxonomic Structure above). The 
fibrillar associates extend in a various directions, 
depending upon the ciliate, and form an elaborate 
cortical cytoskeleton (Figs. 4.10D, 4.11). This 
 cytoskeleton functions both to “passively” support 
the cortex, since disassembly of the microtubules 
changes the form of the cell (Lynn & Zimmerman, 
1981), and to “actively” change cell shape, since 
active sliding of postciliary microtubular ribbons in 
the heterotrich Stentor extends the body after con-
traction (Huang & Pitelka, 1973). Electron micro-
Fig. 4.9. Ultrastructural features of ciliates. A Longitudinal section of the colpodean Colpoda steinii . Note the anterior 
 oral cavity ( OC ), macronucleus ( MA ) with its large nucleolus ( N ), and food vacuoles ( FV ) filled with bacteria ( B ).
B Section through two cortical alveoli ( A ) of the colpodean Colpoda cavicola . Note the thin epiplasmic layer (arrow) 
in this small ciliate. C Section through the pellicle of the colpodean Colpoda magna . Note the much thicker epiplas-
mic layer (arrow) in this large colpodid and the mitochondrion ( M ) with tubular cristae. D A mucocyst in the cortex 
of the colpodean Bresslaua insidiatrix
4.3 Somatic Structures 105
Fig. 4.10. Ultrastructural features of the somatic cortex of ciliates. A Section through a cortical alveolus (A) of the colpo-
dean Colpoda cavicola . Note the epiplasm underlain by overlapping ribbons of cortical microtubules. B Section through 
the pellicle of the colpodean Colpoda magna showing microtubules underlying the thicker epiplasm ( Ep ). C Cross-section 
of the somatic dikinetid of the heterotrichean Climacostomum virens , showing the transverse microtubular ribbon ( T), 
 kinetodesmal fibril ( Kd ), and postciliary microtubular ribbon ( Pc ) (from Peck, Pelvat, Bolivar, & Haller, 1975). D Section