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1978). C Three haptocysts at the tip of the tentacle of the suctorian
Ephelota gemmipara (from Grell & Benwitz, 1984). D The trichocyst of the oligohymenophorean Paramecium 
tetraurelia (from Kersken et al., 1984). E A short toxicyst from the litostomatean Enchelydium polynucleatum (from 
Foissner & Foissner, 1985). F A longitudinal section through the contractile vacuole pore ( CVP ) of the oligohy-
menophorean Colpidium campylum . Note that there is a set of helically disposed microtubules (arrows) supporting 
the pore canal and a set of radially disposed microtubules ( R) that position the contractile vacuole . (from Lynn & 
Didier, 1978.)
4.7 Other Conspicuous Structures 119
120 4. Phylum CILIOPHORA – Conjugating, Ciliated Protists with Nuclear Dualism
reduced or absent (André & Fauré-Fremiet, 1984). 
These mitochondria-like organelles, which cannot 
accomplish oxidative phosphorylation, have inde-
pendently evolved in these several ciliate classes to 
ferment pyruvate into acetate and H 2 , and hence are 
referred to as hydrogenosomes (Fenchel & Finlay, 
1991a). With the isolation of a genome from a cili-
ate hydrogenosome , there is now no doubt that these 
organelles are derived from mitochondria (Boxma 
et al., 2005; van Hoek, Akhmanova, Huynen, & 
Hackstein, 2000a). These anaerobic ciliates often 
have endosymbiotic and ectosymbiotic bacteria , typi-
cally methanogens , associated with the hydrogeno-
somes . This relationship, at least in the case of the 
endosymbiotic methanogens , provides the ciliate 
with increased efficiencies in growth (Fenchel & 
Finlay, 1991b). 
 Finally, a variety of extrusomes are promi-
nent features of the somatic cortex. The different 
orders and classes of ciliates have different types 
of extrusomes (see reviews by Dragesco, 1984a; 
Hausmann, 1978; Rosati & Modeo, 2003). All 
these organelles are membrane-bound, likely syn-
thesized in the endoplasmic reticulum-Golgi sys-
tem, transported to the cell cortex, and stimulated 
to fuse with the plasma membrane by ionic changes 
(Hausmann, 1978). Mucocysts , broadly distributed 
throughout the classes, function to provide a sur-
face coat for the cell, sometimes during the process 
of encystment (Figs. 4.9D, 4.19B) (Lynn & Corliss, 
1991). Upon ejection, both their length and diam-
eter become much larger than those dimensions 
in the resting state (Hausmann, 1978). Possible 
modifications of the mucocysts are the scale-like 
structures or lepidosomes secreted on the surface 
of some haptorians (Foissner, Müller, & Weisse, 
2005a; Nicholls & Lynn, 1984). Clathrocysts and 
 lepidosomes may also be used to construct the cyst 
wall of the haptorian Didinium (Holt & Chapman, 
1971) and the spirotrich Meseres (Foissner 
et al., 2005a). Trichocysts , restricted primarily 
to some nassophoreans and some peniculine oli-
gohymenophoreans , are extrusomes that main-
tain the diameter of the resting state but extend 
as thread-like filaments many times the resting 
length (Fig. 4.19D) (Hausmann, 1978). Trichocysts 
of the peniculine Paramecium appear to func-
tion to protect the ciliate from predators, such 
as Climacostomum , Monodinium , and Dileptus
(Harumoto, 1994; Miyake & Harumoto, 1996; 
Sugibayashi & Harumoto, 2000). 
 While trichocysts may protect their ciliate 
bearer from predators, the last two common cate-
gories of extrusomes – toxicysts and haptocysts 
– enable the ciliate to switch roles and become 
the predator. Toxicysts are typical of the Subclass 
 Haptoria (Class LITOSTOMATEA ), and as the 
name suggests, are extrusomes with toxic poten-
tial. Upon extrusion, their tube-within-a-tube 
structure everts, maintaining the same width as in 
the resting state, but rapidly increasing in length 
to deliver the poisonous material now at the 
tip to the prey (Fig. 4.19E) (Hausmann, 1978). 
The compounds within the toxicyst can enable 
attachment of the predator to its prey and also 
immobilize the prey, partly by causing lysis of the 
somatic cilia (Wessenberg & Antipa, 1969, 1970). 
Finally, haptocysts are typically found at the 
tips of tentacles of the Subclass Suctoria (Class 
 PHYLLOPHARYNGEA ), and are small bottle-
like organelles with a complex internal structure 
(Fig. 4.19C) (Hausmann). When prey contacts the 
suctorian tentacle , the haptocyst everts, cement-
ing the two cells together and rapidly causing the 
prey to become immobile (Benwitz, 1982, 1984). 
Other extrusome types have been described as 
restricted to a particular group, and will be treated 
briefly in the appropriate chapter.