Cap 5

Loxodes
whose response to oxygen concentrations is modi-
fied by light (Fenchel & Finlay, 1986b). 
 Karyorelicteans are predaceous macrophages, 
using their filiform or vermiform bodies to crawl 
between the grains in the sediments in search of 
food. They have been recorded to ingest bacteria , 
Fig. 5.1. Representative genera of the Class KARYORELICTEA. The protostomatid Kentrophoros whose body in 
cross-section is ciliated on one surface (the right?) and harbors a “kitchen garden” of epibiotic bacteria on its glabrous 
zone (after Foissner, 1995a). The loxodid Loxodes whose ventral oral region has a paroral along its right border 
and an intrabuccal kinety extending posteriorly into the tube-like oral cavity. Note the bristle kinety along the ventral 
left surface of the cell (arrow) (after Bardele & Klindworth, 1996). The protostomatid Tracheloraphis showing its 
prostomial oral region and the glabrous zone bordered by the bristle kinety (After Foissner & Dragesco, 1996b). 
The protoheterotrichid Geleia, which is holotrichous and shows a complex oral region of dikinetid files and simple 
polykinetids. (after Dragesco, 1999.)
124 5. Subphylum 1. POSTCILIODESMATOPHORA: Class 1. KARYORELICTEA – The “Dawn” 
 diatoms (e.g., Coscinodiscus , Phaeodactylum ), 
both autotrophic and heterotrophic flagellates 
(e.g., Euglena , dinoflagellates ), other ciliates (e.g., 
Euplotes , Strombidium , and smaller karyorelict-
eans ), and even micrometazoans, such as rotifers 
and copepods (Foissner, 1998b). The many species 
sharing an interstitial habitat probably coexist in 
part by partitioning food resources: different-sized 
Loxodes species coexist in the same lake as the 
larger species consumes the larger food particles 
(Finlay & Berninger, 1984). 
 Conjugation is rarely observed (see Sexuality
and Life Cycle below). Since it does occur in some 
taxa, we presume it to be an ancestral feature of the 
group. Cysts are not known. Thus, explaining the 
presumed global distribution of some of these ciliates
is problematic as it is with any group that does not 
form resistant phases in the life cycle. 
 5.3 Somatic Structures 
 The karyorelictean cell body is typically long, some-
times >5,000 µm, and frequently flattened to about 
5–10 µm in thickness. In several genera, the cell 
surface on which the organism “crawls” is more 
densely ciliated (e.g., Loxodes , Kentrophoros ). The 
body is often pigmented, brown or yellowish, possibly 
due to pigmentocysts or extrusomes . The pigmento-
cysts apparently have a defensive function, at least 
in Loxodes (Buonanno, Saltalamacchia, & Miyake, 
2005). The cell surface may have a conspicuous 
 glycocalyx , but is not underlain by a regular layer of 
cortical alveoli . When present, the alveoli are irregu-
lar and small. Parasomal sacs have not been observed. 
 The somatic dikinetids of these ciliates are com-
posed of two kinetosomes joined by desmoses 
(Fig. 5.2), and oriented at 20–40° to the kinety 
axis. Both kinetosomes may be ciliated or only the 
anterior one. The postciliary microtubular ribbon of 
the posterior kinetosome is divergent, extending up 
to the cortex and posteriorly to overlap the ribbons 
of 10 or more anterior kinetids, and so forming the 
 postciliodesma . The number of overlapping ribbons 
will vary depending upon the contractile state of the 
ciliate, as these microtubules are assumed to play 
the same role in cell elongation as those of Stentor
(Huang & Mazia, 1975; Huang & Pitelka, 1973). It 
is not clear how the organization of the postciliary 
ribbons changes from their origin as a ribbon to the 
modified structure at the cell surface. There are two 
microtubules closest to the kinetosome followed by 
a ribbon of up to 20 microtubules perpendicular to 
the cell surface, and then a single microtubule. This 
2 + ribbon + 1 pattern can be repeated for each over-
lapping set (Fig. 5.2) (Klindworth & Bardele, 1996; 
Raikov, 1994b; Raikov & Kovaleva, 1995; Raikov, 
Gerassimova-Matvejeva, & de Puytorac, 1976). 
The postciliary microtubules are accompanied by 
dense material on either side near their base. The 
posterior kinetosome may also have a tangential 
transverse ribbon associated with triplets 3–5 (Fig. 5.2). 
The kinetodesmal fibril originates near triplets 5, 6, 
and 7 and is variable in form. It is striated and elongate 
in Remanella (Raikov, 1994b), striated and shovel-
shaped in Loxodes (Bardele & Klindworth, 1996), 
and short and hooked with only a faint periodicity 
in Tracheloraphis (Raikov & Kovaleva, 1995) and 
Geleia (de Puytorac, Raikov, & Nouzarède, 1973a). 
The kinetodesmal fibril structure in the latter two 
genera is very reminiscent of Stentor ’s as described 
by Huang and Pitelka. In Loxodes, the shovel-shaped 
kinetodesmal fibril becomes branched, one branch 
of which extends to contact the postciliary ribbon 
of the next anterior kinetid. The anterior kinetosome 
has a tangential transverse ribbon associated with 
triplets 3–5. There may be ribbons of subkinetal 
microtubules that originate from the bases of the 
somatic kinetosomes and extend posteriorly beneath 
the kinety (Raikov & Kovaleva, 1995) or towards 
the left (Klindworth & Bardele, 1996). 
 There are two kineties on the left side of 
Loxodes that have been interpreted to be one 
continuous kinety. Klindworth and Bardele 
(1996) have disproved this by showing that the 
kinetodesmal fibrils are oriented in the manner 
expected for two kineties: these kineties just hap-
pen to abut near the anterior end and so appear to 
be continuous at the level of the light microscope. 
Until it is demonstrated otherwise by electron 
microscopy, we assume that the bristle kineties 
bordering the non-ciliated stripe in Kentrophoros
are bipolar, contrary to the interpretations of 
Foissner (1995a, 1998b). 
 Myonemes are arranged longitudinally and parallel
to the somatic kineties in most karyorelicteans : to 
the right of the kinety in Tracheloraphis , to the 
left of the kinety in Remanella , and on both sides 
in Geleia . Since these ciliates are often not evenly 
ciliated around the body, contraction may cause 
Fig. 5.2. Ultrastructure of the cortex of the Class KARYORELICTEA. A Somatic dikinetids. (a) The protostomatid 
Tracheloraphis (after Raikov & Kovaleva, 1995). (b) The loxodid Loxodes. (after Klindworth & Bardele, 1996.) (c) 
The protoheterotrichid Geleia (after de Puytorac, Raikov, & Nouzarède, 1973a). B Somatic cortex of the protostome 
Tracheloraphis with postciliodesmata composed of overlapping ribbons in the 2 + ribbon + 1 arrangement. (Redrawn 
after Raikov et al., 1976.)
5.3 Somatic Structures 125
126 5. Subphylum 1. POSTCILIODESMATOPHORA: Class 1. KARYORELICTEA – The “Dawn” 
the cell to become banana-shaped or roll up. In 
some species, transverse myonemes occur, possibly 
ensuring an even longitudinal contraction. 
 The contractile vacuole system is not well-
developed, except in freshwater Loxodes species, 
and is often absent. 
 Extrusomes in the karyorelicteans are very diverse. 
 Rhabdocysts have been recorded in Tracheloraphis
and Kentrophoros (Raikov, 1974b), ampullocysts 
in Kentrophoros (Raikov), and cnidocysts and 
 orthonematocysts in Remanella (Foissner, 1996a; 
Raikov, 1978, 1992, 1993). The aberrant character 
of karyorelictean extrusomes in relation to those 
of other ciliates and the apparent similarities of the 
 cnidocysts of some karyorelicteans to the extrusomes 
of dinoflagellates, another alveolate group, have 
been used as another feature to indicate the ancestral 
nature of the karyorelicteans (Raikov, 1992). 
 5.4 Oral Structures 
 The taxa in this class are distinguished from each 
other primarily on the basis of oral structures, 
which, as we learn more about the detailed cyto-
anatomy of this group, are quite diverse. Oral 
kinetosomes bear cilia that are usually slightly 
longer than the somatic cilia, and may have simple 
nematodesmata,