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Abstract This class is truly a riboclass because it 
assembles three groups of ciliates that were never 
suspected of being phylogenetically related, and 
yet there is an extremely strong signal from the 
small subunit rRNA gene sequences that they are. 
The now “classic” plagiopyleans, the sonderiids 
and plagiopylids, are now united with the trimyem-
ids and tentatively also the odontostomatids. These 
ciliates are all considered anaerobic to microaer-
ophilic, and are often found in sapropelic habitats. 
Several species have conspicuous assemblages of 
hydrogenosomes and methanogens, which presum-
ably enable these ciliates to survive in these anoxic 
habitats. There are really no unifying morphologi-
cal features. The somatic kinetids are monokinetids 
in the sonderiids, plagiopylids, and trimyemids and 
highly unusual dikinetids in the odontostomatids. 
Oral structures in the plagiopylids and sonderiids 
are modifi ed extensions of somatic kineties; trimy-
emids apparently have a kind of “circumoral” 
ciliature; and odontostomatids have several small 
oral polykinetids. Stomatogenesis is apparently 
holotelokinetal in all but the odontostomatids, and 
we are ignorant of how this latter group divides. 
There remains much to be learned about their life 
cycle, sexual processes, and nuclear features. 
Keywords Epalxella , Plagiopyla , Trimyema
 The Class PLAGIOPYLEA , like the Class 
 ARMOPHOREA , is in essence a “ riboclass ” – a 
group whose monophyly is based only on the 
evidence of sequences of the small subunit (SSU) 
 rRNA gene . Small and Lynn (1985) established 
the subclass Plagiopylia , including the sonderiids 
and plagiopylids , and transferred these ciliates to 
the Class OLIGOHYMENOPHOREA primarily 
on the basis of the ultrastructure of the somatic 
kinetids. De Puytorac et al. (1993) elevated the 
group to class status, a move supported by Lynn 
and Small (1997). Sequencing of the SSUrRNA 
genes of several species of Trimyema and several 
 plagiopylid genera has now demonstrated these to 
be sister taxa (Baumgartner, Stetter, & Foissner, 
2002; Embley & Finlay, 1994; Lynn & Strüder-
Kypke, 2002). Stoeck, Foissner, and Lynn (2007) 
have evidence that the SSUrRNA gene sequence of 
the odontostomatid Epalxella clusters with strong 
support with these plagiopyleans , and so we have 
made the risky decision to assign the odontosto-
matids to this class as the second order, beside the 
Order Plagiopylida . 
 The plagiopyleans are anaerobic or microaer-
ophilic ciliates that range in size from about 15 µm 
in length but rarely exceed 200 µm in length. They 
are typically ovoid or elongate in body shape and 
not contractile or flexible. In the larger genera, 
such as Lechriopyla and Sonderia , the ciliation is 
holotrichous. In smaller forms, such as trimyem-
ids and odontostomatids , the number of somatic 
kinetids is reduced and much of the body surface 
is non-ciliated. In trimyemids , the kineties even 
appear to spiral, but both light and electron micro-
scopic study of Trimyema refute this interpreta-
tion, and confirm the interpretation proposed by 
Fauré-Fremiet (1962b): the kinetosomes in each 
longitudinally oriented kinety are distributed in 
such a manner that they appear to be spiralling 
(Baumgartner et al., 2002; Detcheva, de Puytorac, 
 Chapter 14 
 Subphylum 2. 
PLAGIOPYLEA – A True Riboclass 
of Uncommon Companions 
& Grolière, 1981). Plagiopyleans are typically 
found in anaerobic freshwater and marine habitats, 
ranging from hydrothermal vents to anoxic marine 
sediments to the intestines of sea urchins and to 
 sewage treatment plants . 
 A notable feature of these ciliates is the pres-
ence of hydrogenosome-methanogen assemblages 
in their cytoplasm in which the methanogens are 
typically sandwiched between hydrogenosomes 
forming groups of up to a dozen units. These 
assemblages have been observed in representatives 
of the order Plagiopylida – in Sonderia (Fenchel, 
Perry, & Thane, 1977), Plagiopyla (Berger & 
Lynn, 1992), and Trimyema (Detcheva et al., 1981). 
However, the “sandwich” pattern can depend upon 
the particular species of methanogen involved: 
Methanocorpusculum parvum is polymorphic – 
ovoid when free in the cytoplasm of Trimyema and 
profusely dentate when associated with its hydrog-
enosomes (Finlay, Embley, & Fenchel, 1993). 
 Biochemical analyses supported the conclusion
that the ciliate organelles are not mitochondria , but 
rather are hydrogenosomes : they exhibit hydroge-
nase activity (Zwart et al., 1988) and do not dem-
onstrate cytochromes , cytochrome oxidase , and 
 catalase activities (Goosen, Wagener, & Stumm, 
1990). There are now techniques for culturing 
both Trimyema (Wagener & Pfennig, 1987) and 
Plagiopyla (Fenchel & Finlay, 1991c), using 
 bacteria isolated from the environment or cultured 
bacterial strains. Furthermore, electromigration 
has been used to concentrate these ciliates from 
environmental sludge samples (Wagener, Stumm, 
& Vogels, 1986) and from mass cultures to enable 
biochemical research (Broers, Molhuizen, Stumm, 
& Vogels, 1992). 
 The name of the class PLAGIOPYLEA is derived 
from the Greek words, plagios meaning oblique 
and pylon meaning gate. This refers to the nature 
of the oral opening in plagiopylids , which is an 
oblique slit whose walls are covered by extensions 
of the somatic kineties. While the somatic kinetid 
of plagiopylids bears some resemblance to that 
of the oligohymenophoreans , the odontostomatid 
dikinetid is quite different (see below Somatic
Structures ). There is no morphological synapo-
morphy for the class, and so it was designated as 
one of the “ riboclasses ” of ciliates by Lynn (2004), 
since SSUrRNA gene sequences appear to be the 
only “strong” characters that support the clade. 
 14.1 Taxonomic Structure 
 Corliss (1979) retained both the plagiopylids and 
 trimyemids in the Order Trichostomatida , following
research by Fauré-Fremiet (1950a, 1962b, 1973) 
among others. Corliss did note that this order 
was a rather heterogeneous taxon with respect 
to the morphological diversity of the families 
placed in it. De Puytorac, Grain, Legendre, and 
Devaux (1984) used a phenetic analysis to place 
the trimyemids in an order Trimyemida in the 
subclass Gymnostomia , while de Puytorac, Grain, 
and Legendre (1994) used parsimony methods 
to provisionally place Trimyema adjacent to the 
 phyllopharyngeans and vestibuliferians , noting that 
stomatogenetic characters might lead to reconsid-
eration of this result. Berger and Lynn (1984) noted 
a peculiar microtubular ribbon associated with 
triplets 2, 3, tentatively unique for the plagiopylids . 
Partly based on this mistaken interpretation (see 
Somatic Structures ), Small and Lynn (1985) 
established the subclass Plagiopylia within the 
Class OLIGOHYMENOPHOREA , based on fea-
tures of the somatic kinetid, which had long anteri-
orly extending kinetodesmal fibrils and a divergent 
postciliary ribbon similar to that of other oligohy-
menophoreans . De Puytorac et al. (1993) elevated 
the subclass to the Class PLAGIOPYLEA . This 
position was maintained by de Puytorac (1994c) 
for the plagiopylids and sonderiids , although he 
placed the trimyemids in the subclass Prostomatia , 
based on the assumption that the oral dikinetids 
were homologues of the prostomatean brosse . 
 Lynn and Small (1997) also recognized the 
Class PLAGIOPYLEA , and included in it both 
 plagiopylids , sonderiids , and trimyemids (Lynn 
& Small, 2002). This was rationalized by simi-
larities in the somatic kinetids with their anteriorly 
directed kinetodesmal fibrils . To these features, we 
can now add the typical sandwich-like arrangement 
of the hydrogenosome-methanogen assemblages in 
 plagiopylids . Finally, SSUrRNA genesequences 
clearly confirmed plagiopylids and trimyemids as 
sister taxa (Baumgartner et al., 2002; Embley & 
Finlay, 1994; Lynn & Strüder-Kypke, 2002). To 
these, we can now add the odontostomatids , based 
on the SSUrRNA gene sequence of the odontosto-
matid Epalxella (Stoeck et al., 2007). We currently 
recognize two orders: the Order Plagiopylida and 
the Order Odontostomatida . 
 The Order Plagiopylida is characterized by 
the typical sandwich-like arrangement of the 
 hydrogenosome-methanogen assemblages. This 
order includes the families, Plagiopylidae , SONDERI-
IDAE , and TRIMYEMIDAE . Genera in the former 
two families typically have a striated band structure 
(see Somatic Structure ), which trimyemids lack. 
 The Order Odontostomatida was established as 
a group by Lauterborn (1908), and remains one 
of the smallest ordinal groups outside those that 
are monotypic (e.g., Licnophorida , Phacodiniida , 
 Protocruziida ). It includes three families: 
the Epalxellidae , the Mylestomatidae , and the 
 Discomorphellidae . These are typically small cili-
ates with a prominent dorsal keel and often elon-
gate, spine-like processes. The somatic ciliature 
is reduced to what are considered vestiges of 
the perizonal kineties of armophorid ciliates, to 
which odontostomatids were originally related 
(Jankowski, 1964b; Tuffrau, 1992; Tuffrau & de 
Puytorac, 1994). 
 14.2 Life History and Ecology 
 Plagiopylids and odontostomatids are key indicators 
of the ciliate sulfureta community, which also 
includes ciliates from the Classes HETERO-
(Dyer, 1989; Fenchel, 1987). They are consistently 
represented in surveys of these habitats, which 
are characterized primarily as being anoxic or 
at most with very low concentrations of oxygen. 
 Plagiopyleans have been found in freshwater habi-
tats in Europe (Finlay & Maberly, 2000; Madoni & 
Sartore, 2003; Sola, Guinea, Longás, & Fernández-
Galiano, 1988), Africa (Dragesco, 1972), and North 
America (Bamforth, 1963; Beaver & Crisman, 
1989b), and in chloride lakes (Madoni, 1990). 
They are typically restricted to the sediment layers, 
often in microhabitats with high concentrations of 
dissolved sulphide (Esteban, Finlay, & Embley, 
1993) and of mesotrophic to hypereutrophic sta-
tus (Beaver & Crisman). Plagiopyleans have 
also been observed in the coastal sediments and 
sands of marine and estuarine habitats in Eurasia 
(Agamaliev, 1974; Dragesco, 1962; Fauré-Fremiet, 
1973; Fauré-Fremiet & Tuffrau, 1955; Fenchel 
et al., 1977), North America (Borror, 1963; Dyer, 
1989; Nerad, Schaffer, Small, & Mangold, 1995), 
the Gulf of Arabia (Al-Rasheid, 1999b), and the 
 Sea of Japan (Ozaki & Yagiu, 1941). Plagiopyla
may extend its distribution into the water column 
of marine habitats when the oxycline changes 
its vertical placement as the seasons progress 
(Fenchel, Kristensen, & Rasmussen, 1990). Where 
abundances have been recorded in the water col-
umn, Plagiopyla rarely exceeds 1 ml −1 (Fenchel et 
al., 1990; Massana & Pedrós-Alió, 1994), while 
 odontostomatids can increase their relative abun-
dance in sediments during periods of anoxia, reaching 
more than 50 ml −1 of sediment (Fenchel, 1993). 
 Plagiopyleans have never been recorded from soils 
(Foissner, 1998a). 
 Plagiopyleans have also been conspicuous endo-
symbionts from hosts as diverse as sea urchins 
(Grolière, de Puytorac, & Grain, 1980b; Lynch, 
1930; Poljansky & Golikova, 1959) and the hip-
popotamus (Thurston & Grain, 1971). 
 Our understanding of feeding and growth in 
 plagiopyleans is primarily derived from research 
on Trimyema and Plagiopyla . Strains of Trimyema 
compressum have been fed over 50 strains of bacte-
ria , including both Gram-positive and Gram-negative 
species, as well as a variety of methanogens . 
This ciliate indiscriminantly ingested all bacteria 
(Schulz, Wagener, & Pfennig, 1990). However, 
its growth was limited to a smaller subset of the 
strains, although both Gram-positive and Gram-
negative strains and strains of Archaea supported 
some growth (Baumgartner et al., 2002; Schulz et al.,
1990; Yamada, Kamagata, Nakamura, Inamori, & 
Nakamura, 1994). Bacterial carbohydrates are the 
most important energy source for these anaerobic 
ciliates (Holler, Gälle, & Pfennig, 1994). Yields 
of over 9,000 ciliates ml −1 were recorded when 
T. compressum ingested a strain of Desulfovibrio 
vulgaris (Yamada et al., 1994). Threshold concen-
trations of bacteria to support growth were in the 
range of 10 7 ml −1 (Schulz et al., 1990). Plagiopyla 
nasuta has been grown on a mixed assemblage of 
natural sediment-derived bacteria and its feeding 
and growth dynamics studied by uptake of fluores-
cently labeled bacteria (FLB) (Massana, Stumm, 
& Pedrós-Alió, 1994). Plagiopyla could consume 
over 4,000 bacteria ciliate −1 h −1 but had growth 
rates that were very low compared to aerobic 
ciliates of similar size feeding at these uptake rates 
(Massana et al., 1994). This confirms the general 
view that gross growth efficiency of these anaerobic 
14.2 Life History and Ecology 271
ciliates is about 25% that of aerobes, although 
it can be increased by the presence of symbiotic 
 methanogens (Fenchel & Finlay, 1990b, 1991a, 
1991b). In the field, the realized growth rates 
of Plagiopyla are much lower. Thus, the natural 
abundances of these ciliates are unlikely to exert 
control on natural bacterial populations (Massana 
& Pedrós-Alió, 1994). 
 Plagiopyleans have conspicuous and abundant 
symbiotic bacteria associated both as ectosymbi-
onts and as endosymbionts (Fenchel et al., 1977; 
Berger & Lynn, 1984). It is now clear that these 
endosymbiotic associations have been estab-
lished repeatedly, and therefore have also been 
lost repeatedly. Wagener, Bardele, and Pfennig 
(1990) demonstrated that Methanobacterium 
formicicum could be functionally integrated into 
Trimyema cells that were endosymbiont-free. In 
natural populations, repeated losses and functional 
integration are demonstrated by the sister spe-
cies P. nasuta and Plagiopyla frontata that have 
endosymbionts related to the different methanogen 
genera Methanocorpusculum and Methanolobus , 
respectively (Embley & Finlay, 1994). As noted 
above, this symbiotic association increases the 
 growth efficiency of the ciliate. Moreover, it is 
mutualistic as it also provides a refuge for the 
 methanogens , which avoid competition with sul-
phate reducing bacteria , avoid the toxic effects of 
environmental oxygen, and have a ready supply of 
 hydrogen (Fenchel & Finlay, 1992; Müller, 1993). 
Plagiopyla frontata may have over 3,000 methano-
gens per cell. The cell division of these bacteria, 
which is synchronous with their host ciliate’s cell 
division, may be controlled somehow by the ciliate. 
Excess bacterial production is transferred to the 
ciliate host in a fashion similar to the endosymbio-
sis with Chlorella species found in other ciliates 
(Fenchel & Finlay, 1991c). 
 14.3 Somatic Structure 
 Plagiopylids are ovoid to elongate ovoid ciliates that 
may show some dorsoventral flattening (Fig. 14.1). 
 Odontostomatids are laterally-compressed ciliates 
with a rigid and often ribbed, armor-like pellicle. 
Spiny processes are often present, both posteriorly 
and anteriorly (Fig. 14.2). Trimyemids and odonto-
stomatids can be about 15 µm in length while some 
 plagiopylids can exceed 200 µm in length (Nerad 
et al., 1995; Sola, Guinea, Longás, & Fernández–
Galiano, 1989b). Trimyemids have an apparently 
helicoidally disposed and sparse somatic ciliature 
(Fig. 14.1). The helicoidal disposition is due to the 
patterning of kinetids in the up to 60 somatic kine-
ties in some species. Trimyemids may also have a 
 caudal cilium complex, which Baumgartner et al. 
(2002) interpretedto 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 kinetodesmalfibrils that borders the oral region on the anterior, 
left, and posterior portions (Detcheva et al., 1981; 
Serrano, Martín-González, & Fernández-Galiano, 
1988). This row may be accompanied by a second 
row interior to it and perhaps even a third shorter 
fragment (Fig. 14.1) (Serrano et al., 1988). We 
could tentatively interpret Figure 6 of Detcheva 
et al. (1981) as indicating that the outer kinetosomes 
have postciliary ribbons and a kinetodesmal fibril 
while the inner kinetosomes have only a tangen-
tial transverse ribbon. There are no ultrastructural 
observations for the second set of oral structures 
in trimyemids : these oral dikinetids lie on the 
right side of the oral region, and can range from 
four independent dikinetids to two polykinetids, 
each composed of three dikinetids (Fig. 14.1) 
(cf. Baumgartner et al., 2002; Nerad et al., 1995; 
Serrano et al., 1988). 
 The sonderiids and plagiopylids share a basic 
plan to the oral ciliature, which lines a ventral 
transverse oral groove that becomes tubular as it 
extends inwards towards the cytostome. After a 
slight break, the ends of the somatic kineties that 
border the anterior (= dorsal) lip and posterior 
(= ventral) lip become much more densely packed 
with kinetosomes (Fig. 14.1) (Lynch, 1930; Serrano 
et al., 1988; Sola et al., 1988). In Plagiopyla , the 
density of the kinetosomes becomes thinner as these 
oral kineties extend to line the oral cavity (Sola 
et al., 1988). Small and Lynn (1985) distinguished 
genera based on the trajectory of the oral invagina-
tion: the oral cavity of Plagiopyla extends to the 
left while that of Paraplagiopyla extends directly 
dorsally. The oral kinetosomes of Plagiopyla and 
Lechriopyla lack “somatic” fibrillar associates 
but do have alveoli between them and parasomal 
sacs to the side. Microtubules of unknown origin 
have been observed between these oral kineties (de 
Puytorac et al., 1985). Two to three fibrous rootlets 
arise at the base of each of these kinetosomes and 
extend parallel to the cell surface. Rootlets from 
adjacent kinetosomes intertwine forming a com-
plex cytoskeletal structure that departs from each 
kinety and assembles into an aggregate, which 
in Lechriopyla is fork-shaped and called the fur-
cula (Berger & Lynn, 1984; Lynch, 1930). The 
cytopharynx is lined by ribbons of microtubules 
whose origin is undetermined. 
 14.5 Division and Morphogenesis 
 Plagiopyleans divide while swimming freely. There 
are only two recent studies of division morphogen-
esis in plagiopyleans , and no reports of stoma-
togenesis in odontostomatids . 
 Division morphogenesis in Plagiopyla has been 
redescribed by de Puytorac et al. (1985). It begins 
by kinetosomal replication occurring at the equator 
especially on the posterior side of the putative fission
Fig. 14.4. Division morphogenesis of plagiopylids . A In the plagiopylid Plagiopyla , kinetosomal replication occurs 
at the anterior ends of all the somatic kineties ( a – d ). A set of kinetosomes appears in the fission furrow in the right 
dorsal area, and these may give rise to oral kinetosomes ( b – d ). (from de Puytorac et al., 1985.) B In the trimyemid
Trimyema , a file of kinetosomes appears in the ventral anterior region ( a ) and this appears to organize into a file and 
two polykinetids of six kinetosomes. (from Serrano et al., 1988.)
furrow where the kinetosomes become dense as 
replication proceeds, approaching a density simi-
lar to that of the proter’s oral kineties (Fig. 14.4).
De Puytorac et al. (1985) remarked on the appear-
ance in the right dorsal portion of the fission fur-
row of a field of irregularly arranged kinetosomes 
whose destiny remains to be determined (Fig. 
14.4). Could these be the homologues of the diki-
netids found in the oral region of trimyemids ? 
 Serrano et al. (1988) demonstrated that Trimyema
has a kind of holotelokinetal stomatogenesis . These 
authors claimed that kinetosomes from Kinety n
also participate to form the dikinetids and the third 
inner row of kinetosomes (Fig. 14.4). However, 
this claim needs to be confirmed by demonstrating 
the intermediate stages to definitively justify this 
conclusion. What appears probable is that the outer 
two rows of the “ circumoral ” arise from the two 
anterior kinetosomes of each somatic kinety. 
 14.6 Nuclei, Sexuality 
and Life Cycle 
 The plagiopylean macronucleus is homomerous , 
ranging in shape from globular in the small odonto-
stomatids and trimyemids to an elongate ellipsoid 
in larger sonderiids . Some odontostomatids can 
have multiple macronuclei (Figs. 14.1, 14.2). The 
 macronucleus is typically accompanied by a sin-
gle, globular micronucleus . Fauré-Fremiet (1973) 
noted that Parasonderia kahli had a highly unusual 
macronucleus: it was triangular in shape, flattened, 
and wrapped around the tubular oral cavity of this 
 To our knowledge, there are no reports of con-
jugation in plagiopyleans . Thus, their genetics and 
details of nuclear development and differentiation 
remain to be determined. 
14.6 Nuclei, Sexuality and Life Cycle 277