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to demonstrate affinities with 
the caudal cilium complex of oligohymenopho-
reans . The larger plagiopylids and sonderiids are 
typically holotrichous and densely ciliated (Fig. 
14.1). Paraplagiopyla , if truly a plagiopylean , is 
an exception as its somatic kineties are restricted 
to a narrow furrow that extends around the edges 
of the flattened cell (Thurston & Grain, 1971). The 
somatic ciliature of odontostomatids is typically 
reduced to anterior and posterior cirrus-like tufts, 
although the infraciliature probably persists as non-
ciliated kinetosomes (Fig. 14.2). 
 Only four studies have been published on which 
to base the description of the cortical ultrastructure 
of plagiopyleans (Berger & Lynn, 1984; Detcheva 
et al., 1981; de Puytorac et al., 1985; Schrenk & 
Bardele, 1991). 
 The plasma membrane is covered by a thin 
 glycocalyx , which can appear somewhat granular 
(de Puytorac et al., 1985). The alveoli in plagi-
opylids are well developed and lie on a thin 
 epiplasmic layer . Schrenk and Bardele (1991) 
claimed that the alveolar layer is absent in the 
 odontostomatid Saprodinium in which the cell 
membrane is underlain only by a thick epiplasmic 
layer . The cortex is ridged with kinetosomes lying 
between the ridges in trimyemids and at the tops of 
the ridges in plagiopylids . 
 The kinetids of plagiopyleans can still only 
be tentatively characterized, and they differ dra-
matically between plagiopylids and odontosto-
matids (Fig. 14.3). However, it now appears that 
the characterization of the plagiopylid kinetid by 
Berger and Lynn (1984) was incorrect, and that the 
microtubular ribbon they interpreted as an unusual, 
anteriorly-directed transverse ribbon is probably 
a kind of basal microtubular system. The somatic 
kinetids are monokinetids with a divergent postcili-
ary ribbon that extends into the cortical ridges. The 
well-developed, anteriorly-directed kinetodesmal 
fibril originates near triplets 5, 6, 7 (Fig. 14.3). 
The orientation of the transverse ribbon has not 
Fig. 14.1. Stylized drawings of representatives of the Order Plagiopylida in the Class PLAGIOPYLEA The plagi-
opylid Plagiopyla . The sonderiid Sonderia . The trimyemid Trimyema . Note the striated band on the right side of 
14.3 Somatic Structure 273
been definitively proven, although published and 
unpublished micrographs (C. Bardele, personal 
communication 2006; D. Lynn, 2006) suggest a 
radial orientation adjacent to triplet 4 and a very 
short trajectory, underlain by dense material, into 
the adjacent cortical ridge (Fig. 14.3). The overall 
pattern is very similar to that of the hymenostomes 
(see Chapter 15 ). Dense material adjacent to the 
base of the kinetosome near triplets 2, 3 provides 
the origin of several longitudinally orientated 
microtubules that extend along the left side of 
the kinety in Lechriopyla . These were originally 
interpreted incorrectly as transverse microtubules 
(Berger & Lynn, 1984). A parasomal sac is found 
anterior to the kinetosome. 
 The somatic kinetids of odontostomatids are also 
accompanied by parasomal sacs . However, odon-
tostomatids have dikinetids, not monokinetids, 
throughout the cortex, although not all are cili-
ated (Fig. 14.3) (Schrenk & Bardele, 1991; Sola, 
Serrano, Guinea, & Longás, 1992). The odonto-
stomatid somatic dikinetids can be characterized 
as follows: a ciliated anterior kinetosome that has 
a tangential transverse ribbon of microtubules 
associated with triplets 4, 5; and a ciliated poste-
rior kinetosome with a divergent postciliary rib-
bon. Cathetodesmal-like fibrils may originate near 
triplet 2 on the anterior kinetosome (Fig. 14.3). 
Schrenk and Bardele (1991) concluded that there 
is no kinetodesmal fibril although there is a dense 
structure in the appropriate position near the pos-
terior kinetosome and Sola et al. (1992) reported 
 kinetodesmal fibrils adjacent to some anterior and 
posterior kinetosomes in the light microscopic 
description of Saprodinium . In the non-ciliated 
regions of the cortex, Saprodinium has its diki-
netid kinetosomes without fibrillar associates and 
separated by extremely inflated parasomal sacs , 
which may be used for endocytosis (Schrenk & 
Bardele, 1991). An inverse kinety , whose origin is 
unclear, lies to the left of the oral region (Schrenk 
& Bardele, 1991; Sola et al., 1992). 
 A unique feature of the cortex of most plagi-
opylids and sonderiids , a feature that might suggest
establishment of a subordinal category for mem-
bers of these two families, is the striated band 
(Fig. 14.1) (Lynch, 1930). This band extends from 
the right side of the oral opening, in parallel with 
adjacent somatic kineties, sometimes turning ante-
riorly before turning posteriorly to extend almost to 
the posterior pole. It is composed of a series of thin 
ridge-like lamellae of cytoplasm, about 2 µm high, 
overlain by flattened cortical alveoli. The walls of 
the striated band appear to be supported by 8–9 
macrotubules (Berger & Lynn, 1984). The function 
of the striated band is unknown. 
 Plagiopylids and sonderiids have conspicuous 
rod-shaped extrusomes , which may be up to 20 µm 
Fig. 14.2. Stylized drawings of representatives of the Order Odontostomatida in the Class PLAGIOPYLEA . The 
 discomorphellid Discomorphella . The epalxellid Saprodinium
in length (Fauré-Fremiet & Tuffrau, 1955). On 
extrusion, the matrix extends as a striated rod 
from a retained cylindrical envelope (Berger & 
Lynn, 1984). Trimyemids have spheroidal muco-
cysts (Baumgartner et al., 2002; Detcheva et al., 
1981) while Plagiopyla may also have some 
Fig. 14.3. A Schematics of the somatic kinetids of the Class PLAGIOPYLEA . ( a ) Monokinetid of Plagiopyla . ( b ) 
Monokinetid of Trimyema . ( c ) Dikinetid of Saprodinium (from Lynn, 1981, 1991). B Somatic cortex of a typical 
 plagiopylid based on the somatic cortex of Plagiopyla and Lechriopyla
14.3 Somatic Structure 275
smaller extrusomes (de Puytorac et al., 1985). 
 Mucocysts have not been observed in odontosto-
matids (Schrenk & Bardele, 1991). 
 Plagiopyleans do not have mitochondria, but 
rather “microbodies” without cristae that are now 
known to be hydrogenosomes (see Life History 
and Ecology ) (Goosen et al., 1990; Zwart et al., 
 A contractile vacuole and a cytoproct are typi-
cally found in the posterior one-third of the cell. 
 14.4 Oral Structures 
 The oral structures divide the plagiopyleans into 
three groups – the odontostomatids , the trimyem-
ids , and the sonderiids and plagiopylids (Figs. 14.1, 
14.2). Whether detailed and careful ultrastructural 
investigations will eventually reveal homologies, at 
this stage we must treat them quite separately. 
 Odontostomatids have a small and complex oral 
cavity with a reduced number of oral polykinetids , 
typically less than a dozen (Schrenk & Bardele, 
1991; Sola et al., 1992; Tuffrau, 1992). They are 
composed of three rows of kinetosomes, which are 
hexagonally packed, but only the oral polykinetid 
closest to the cytostome has fibrillar associates that 
are interpreted as postciliary ribbons (Schrenk & 
Bardele, 1991). These latter authors speculated 
that the oral region of Saprodinium , and perhaps 
other odontostomatids , is in an inverse orientation, 
but this will have to await morphogenetic studies. 
 Odontostomatids may also have two files of paroral
cilia (see Sola et al., 1992; Tuffrau, 1992), but this 
has not been confirmed by electron microscopy 
(Schrenk & Bardele, 1991). 
 The trimyemids have always been classified 
among ciliates with a simple oral ciliature and oral 
apparatus. It is now certain that they have at least 
an outer row of kinetosomes with kinetodesmal