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1984; Grim, 1982; Tuffrau & Fleury, 1994). 
Some oligotrichs , such as Strombidium , have 
numerous polygonal, cortical platelets of polysac-
charide , which typically underlie the cortex in the 
posterior portion of the body. Coloration can be 
quite variable in spirotrichs , due to the presence 
of pigment granules , sequestered prey chloroplasts 
(see Life History ), and Chlorella symbionts. The 
color and nature of the granules can be important 
features to distinguish species (e.g., Berger & 
Foissner, 1987, 1989a). 
 Since the somatic kinetids of the different sub-
classes appear to be quite different, we will deal 
briefly with a characterization of the somatic 
kinetids of each subclass, treating the stichotrichs 
and hypotrichs together for comparative purposes. 
Protocruzia is the only genus in the Subclass 
 Protocruziidia (Fig. 7.2). Grolière et al. (1980a) 
described its kinetids, which may be characterized 
as follows: a ciliated anterior kinetosome bearing 
a tangential transverse ribbon at triplets 4 and 5; 
a ciliated posterior kinetosome bearing a smaller 
transverse ribbon of 1–2 microtubules near triplet 
4, a set of 10–15 divergent posticiliary microtubules
that extend posteriorly to slightly overlap adjacent 
sets, and a striated kinetodesmal fibril at triplets 5 
and 6 that extends to the right and anterior but does 
not overlap the fibril of the next anterior kinetid 
(Fig. 7.5). Although the postciliary ribbons are 
large, they do not form postciliodesmata as typical 
of the Class HETEROTRICHEA (see Chapter 6 ). 
Phacodinium is the only genus in the Subclass 
 Phacodiniidia (Fig. 7.2). It is characterized as hav-
ing linear somatic polykinetids composed of up 
to nine linked ciliated kinetosomes. There is dor-
soventral differentiation of these polykinetids: on 
the dorsal surface, there are 1–3 kinetosomes with 
only one cilium; and, on the ventral surface, there 
are 9–11 ciliated kinetosomes (Fernández-Galiano 
& Calvo, 1992). Each kinetosome has the classi-
cal fibrillar associates: a very slightly convergent 
 postciliary ribbon that extends posteriad; a short, 
tapering, laterally-directed kinetodesmal fibril that 
arises near triplets 5–7, and a tangentially-oriented 
 transverse ribbon that extends a short distance 
laterally into the adjacent ridge from triplets 3 and 
4 (Fig. 7.5) (Didier & Dragesco, 1979). There are 
some polykinetids with “two” files of kinetosomes. 
These “homologues of cirri” are seemingly organ-
ized in a zig-zag pattern with each kinetosome 
retaining all its fibrillar associates (Da Silva 
Neto, 1993a).
Fig. 7.5. Schematics of the somatic kinetids of representatives of the Class SPIROTRICHEA . ( a ) Dikinetid of 
Protocruzia . ( b ) Linear polykinetid of Phacodinium . ( c ) Dorsal dikinetid of Euplotes . ( d ) Somatic dikinetid of 
Transitella . ( e ) Dorsal dikinetid of Stylonychia . ( f ) Ventral dikinetid of Engelmanniella . (from Lynn, 1981, 1991.)
7.3 Somatic Structures 157
Licnophora is one of two genera in the Subclass 
 Licnophoria (Fig. 7.2). Its hourglass shape has 
the adoral zone at the ‘anterior’ and several rings 
of cilia surrounding the ‘posterior’ attachment 
disk (Van As et al., 1999). The ultrastructure of 
these somatic structures is highly complex and 
not similar to any of the dikinetid structures so far 
described (Da Silva Neto, 1994a). 
 The infraciliature of Subclasses Oligotrichia 
and Choreotrichia has only recently been the 
subject of detailed studies, and there is consider-
able variation in somatic kinetid pattern (Fig. 7.3). 
 Strombidiid oligotrichs typically have a girdle 
kinety that may be composed of monokinetids in 
Strombidium species (Agatha, 2004a, 2004b; Lynn, 
Montagnes, & Small, 1988) or dikinetids (Lynn & 
Gilron, 1993; Petz & Foissner, 1992). The ventral 
kinety has at least a posterior portion that is always 
composed of dikinetids (Agatha, 2004a, 2004b; 
Lynn & Gilron, 1993; Lynn et al., 1988). There 
has been no ultrastructural study of these somatic 
kinetids . Choreotrichs are also variable in somatic 
kinetid structure. Although Strombidinopsis spe-
cies typically have somatic dikinetids distributed 
in bipolar somatic kineties (Fig. 7.3) (Lynn et al., 
1991c), tintinnids can have both monokinetids 
and dikinetids in their somatic kineties (Fig. 7.3) 
(Agatha & Strüder-Kypke, 2007; Choi et al., 
1992; Foissner & Wilbert, 1979; Laval-Peuto & 
Brownlee, 1986). Among other aloricate choreot-
richs , Strobilidium species have somatic monoki-
netids while Leegaardiella and Lohmanniella have 
 somatic dikinetids (Agatha & Strüder-Kypke, 
2007; Lynn & Montagnes, 1988; Montagnes & 
Lynn, 1991; Petz & Foissner, 1992). Strobilidium
species have ciliated somatic monokinetids whose 
cilia extend out under a cortical ridge, parallel to 
the cell surface (Fig. 7.3) (Grim & Halcrow, 1979); 
The kinetid appears to have a bilayered transverse 
ribbon composed of an anterior and posterior row 
of microtubules (Grim, 1987). 
 Corliss (1979) classified members of our 
Subclasses Hypotrichia and Stichotrichia in the 
Order Hypotrichida while Tuffrau and Fleury (1994) 
placed them both in their Class HYPOTRICHEA . 
This view is based on the strong resemblances in 
the global patterning of the infraciliatures of both 
groups: a ventral infraciliature of scattered cirri
and a dorsal infraciliature of widely spaced files of 
dikinetids. Marginal cirri may be distributed along 
the body edges, delimiting the dorsal and ventral 
surfaces. Ventral cirri can be arranged in anterior-
posterior files (e.g., Urostyla , Kahliella , Plagiotoma ) 
or more asymmetrically scattered (e.g., Diophrys , 
Euplotes , Oxytricha , Stylonychia ) (Figs. 7.2, 7.4). 
Small and Lynn (1985) emphasized that the subtle 
differences in kinetid structure meant that these 
two groups were not closely related, and they 
separated them into the Subclasses Hypotrichia and 
 Stichotrichia , even placing them in separate classes 
(see above) while Fleury et al. (1985b) had placed 
them in separate suborders. Division morphogen-
esis in hypotrichs and stichotrichs is also different 
(see below) while SSUrRNA gene sequences sepa-
rate them at some distance from each other (e.g., 
Bernhard et al., 2001). The dorsal dikinetids of 
hypotrichs are characterized as follows: a ciliated 
anterior kinetosome with a tangential transverse 
ribbon , probably near triplets 3-5 and sometimes 
a single postciliary microtubule ; a posterior kineto-
some with a short condylocilium , a divergent 
postciliary ribbon, and a laterally-directed, striated 
 kinetodesmal fibril at triplets 6, 7 (Fig. 7.5) (Lenzi 
& Rosati, 1993; Lynn, 1991; Rosati, Verni, Bracchi, 
& Dini, 1987; Wicklow, 1983). Lasiosomes , whose 
function is not known, may be associated with the 
axonemal base of the anterior cilium while ampules 
may surround the kinetid in some euplotids (e.g., 
Ruffolo, 1976a; Görtz, 1982a). The stichotrich 
dorsal dikinetid is much more variable but typically 
is characterized as: the ciliated anterior kinetosome 
bears a tangential transverse ribbon ; the non-cili-
ated posterior kinetosome, if present, bears a small 
 divergent postciliary ribbon and typically loses its 
 kinetodesmal fibril during development (Fig. 7.5) 
(Fleury et al., 1986; Görtz, 1982a; Grimes & Adler, 
1976; Lynn, 1991). 
 The ventral somatic kinetids of hypotrichs and 
 stichotrichs are typically polykinetids, called cirri . 
These complex ciliary structures enable the complex 
movements of hypotrichs and stichotrichs, allow-
ing them to rapidly dart a short distance forward, 
quickly withdraw, and change directions rapidly 
(e.g., Erra, Iervasi, Ricci, & Banchetti, 2001; Ricci, 
1990). However, cirri undoubtedly develop from 
the assembly of dikinetid units (see Division and 
Morphogenesis ;