Logo Passei Direto

A maior rede de estudos do Brasil

14 pág.
Cap 12

Pré-visualização | Página 5 de 7

1979a, 1979b). Mucocyst abundance varies through-
out the life cycle with depletions in their abundance 
 correlated with encystment (Delmonte Corrado 
et al., 1996; Suhama, 1969). 
 Mitochondria are the typical tubular forms 
characteristic of ciliates. They may be distributed 
throughout the cortex or anchored in the cortex, 
possibly by filamentous elements associated with 
the microtubular ribbons of the somatic kinetids 
(Lynn, 1977a). 
 The cytoproct , when it has been described, is usu-
ally located near the contractile vacuole (Foissner, 
 12.4 Oral Structures 
 Colpodeans have a permanent cytostome and an 
oral cavity that is typically in the anterior third 
of the cell (Figs. 12.1, 12.2). Marynids with their 
posterior oral cavity are an exception to this general 
description (Foissner, 1993a). The size of the oral 
apparatus essentially varies with body size: the 
larger ciliates, such as Bursaria , typically have 
a larger oral cavity (Fig. 12.1). However, this is 
not always the case. Some carnivorous colpodids, 
like Bresslaua , are smaller than some of the larger 
bacterivorous species of Colpoda (e.g., Colpoda
magna ) (Foissner, 1993a). As noted in Chapter 1 , 
the colpodeans superficially have extremely vari-
able oral structures (Fig. 1.4) (Foissner, 1993a). 
However, upon closer examination and especially 
through detailed analyses of stomatogenesis (see 
below Division and Morphogenesis ), there is an 
underlying unity to the diversity of patterns. 
Fig. 12.4. Somatic cortex of a typical colpodean interpreted based on the somatic cortex of several colpodeans , such 
as Colpoda and Bursaria
 The cyrtolophosidids , bursariomorphids , and bry-
ophryids have several to many adoral polykinetids 
oriented along the left side of the oral cavity (Figs. 
12.1, 12.2). These can be composed of a basic two 
rows of kinetosomes, constructed by the side to side 
assembly of dikinetids, joined by dense connec-
tives in a square-packed or hexagonal arrangement. 
A third row can often appear during stomatogenesis 
(Bardele et al., 1991; Didier et al., 1980; Golder 
& Lynn, 1980). Colpodids have a large left oral 
polykinetid composed of regularly spaced rows, 
which may be linked by connectives both within and 
between rows (Garcia-Rodriguez, Perez-Paniagua, 
& Perez-Silva, 1981; Hofmann-Münz, 1991; Lynn, 
1976a, 1976b, 1976c, 1977; Perez-Paniagua et al.,
1979a, 1979b). The single, small adoral polyki-
netid of grossglockneriid colpodids also probably 
has an organized kinetosomal arrangement (Aescht 
et al., 1991; de Puytorac, Didier, Detcheva, & 
Foissner, 1983a). Postciliary ribbons extend from 
these kinetosomes to support the cytopharnynx. 
 The right oral kinetids in the cyrtolophosidids , 
 bursariomorphids , and bryophryids are minimally 
organized as a paroral composed of dikinetids. 
Both kinetosomes are ciliated while the postciliary 
ribbon from the left kinetosome extends to support 
the cytopharynx (Bardele et al., 1991; Didier et al., 
1980; Golder & Lynn, 1980). 
 Hofmann-Münz (1991) was the first to dem-
onstrate that there was some order to the right 
oral field of colpodids , which had been described 
previously as unordered (Garcia-Rodriguez et al., 
1981; Lynn, 1976c, 1977a; Perez-Paniagua et al., 
1979a; but see also Perez-Paniagua & Perez-Silva, 
1978). A dikinetid file may extend along the right 
border of the right oral polykinetid. This “paroral” is 
composed of a single file of kinetosomes whose 
orientation is similar to the left kinetosome of 
the paroral kinetids of the other orders, while 
the right kinetosome of the paroral dikinetids in 
 colpodids is oriented at 180° as judged by the 
orientation of the postciliary microtubules. An 
unordered field of kinetosomes is arrayed to the 
right of this “paroral” (Hofmann-Münz, 1991). In 
the grossglockneriid colpodids , whose oral ciliature
is quite reduced, the right oral ciliature is just a 
single file of kinetosomes bearing a postciliary 
ribbon that extends anteriorly to support the sucker 
(Aescht et al., 1991; de Puytorac et al., 1983a). 
As noted before, the grossglockneriids have a 
small feeding tube , supported by lamellae of 
microtubules reminiscent of the arrangement of the 
 phyllae in the cytopharynx of the phyllopharyngeans 
and presumed to be derived during stomatogen-
esis from postciliary microtubular ribbons (Aescht 
et al.; de Puytorac et al., 1983a). 
 Except for the unusual mycophagous gross-
glockneriids (Petz, Foissner, & Adam, 1993), 
 colpodeans can be characterized as suspension or
 filter feeders . Fenchel (1980a) has described 
Bursaria as an upstream filter feeder , using the 
spacing between its left oral polykinetids to trap 
prey ciliates larger than 8–10 µm, which is the 
average spacing between these structures. Fenchel 
(1980a) was unable to determine which oral struc-
ture of colpodids was responsible for retaining 
the particles since the species that he described 
fed while swimming. The smaller Colpoda steinii
cleared larger particles, about 1 µm diameter, more 
efficiently than the larger Colpoda cucullus , which 
optimally cleared particles slightly less than 0.4 µm 
(Fenchel, 1980b). Since the left oral field of colpo-
dids is ordered, one is tempted to speculate that this 
provides the filter in these species. 
 As in other ciliates, colpodeans form food vacuoles
in which prey digestion occurs (Rudzinska, Jackson, 
& Tuffrau, 1966). 
 12.5 Division and Morphogenesis 
 Colpodeans divide either free-swimming or within 
a cyst . Parental oral structures may be partially 
or completely reorganized. The colpodids are the 
group classically considered to divide in reproductive 
cysts . However, under exceptional circumstances 
even colpodids may divide while swimming freely 
(Stuart, Kidder, & Griffin, 1939). Division within 
a cyst is typically palintomic , that is typically two 
divisions occur with no DNA S-phase occurring 
between them (Foissner, 1993a). 
 Tuffrau (1952) provided details of silver-stained 
dividing colpodids and demonstrated that all 
the parental oral structures dedifferentiated and 
the ciliates were essentially astomatous during 
 palintomy . Following cytokinesis , kinetosomal 
proliferation occurred at the ends of some of 
these somatic kineties to provide kinetosomes for 
the new oral structures (Fig. 12.5). Hashimoto 
(1966) confirmed both that the same kind of 
 stomatogenesis occurred in colpodids excysting 
from resting cysts and that the number of somatic 
12.5 Division and Morphogenesis 253
254 12. Subphylum 2. INTRAMACRONUCLEATA: Class 6. COLPODEA
kineties involved increased as the size of the species
increased. Foissner (1996b) has typed this as 
 merotelokinetal stomatogenesis since the ends 
of only a limited number of somatic kineties are 
involved. Since Tuffrau (1952) and Hashimoto 
(1966), several studies have demonstrated that 
the left oral polykinetid is derived by the fusion 
of “subpolykinetids” composed of three rows of 
kinetosomes, which are initially derived from diki-
netids. The right oral polykinetid is assembled by a 
file of dikinetids along the border of the primordial 
field and to its right there is a field of unordered 
kinetosomes derived by kinetosomal replication 
of somatic kinetosomes (Garcia-Rodriguez et al., 
1981; Perez-Paniagua & Perez-Silva, 1978; Perez-
Paniagua et al., 1979a, 1979b). 
 The pattern in colpodids is undoubtedly derived 
from the pattern demonstrated by representatives 
of the other colpodean orders, at least if we use 
the molecular phylogenies as the basis for polarizing
stomatogenetic patterns in this class. Foissner 
(1996b) characterizes the alternate pattern as pleu-
rotelokinetal since oral kinetosomal proliferation 
occurs within, and sometimes between, several 
kineties on the right side of the body and on 
both sides of the fission zone.