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fibrils 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