A maior rede de estudos do Brasil

10 pág.
Cap 11

Pré-visualização | Página 2 de 5

then gradually decreased in number as 
they became increasingly restricted to the left side 
of the ventral surface (e.g., some Nassula species) 
and then to the left side of the oral region. This ulti-
mately resulted in hymenostome -like ciliates with 
three oral polykinetids (Fig. 11.2) (i.e., Furgasonia , 
Pseudomicrothorax ) – a phylogenetic hypothesis 
that now requires more extensive testing by gene 
sequence data! 
 It is clear that there is a significant amount of 
diversity in the “oral” structures of these ciliates, 
and this has led to substantial high level split-
ting of the taxa. The French researchers have 
11.1 Taxonomic Structure 235
recognized this by supporting six orders within a 
Subclass Nassulia (Deroux, 1994b; de Puytorac, 
1994a). Jankowski (1968a) recognized two subor-
ders within his Order Ambihymenida . Given that 
relatively little taxonomic research has focused on 
these ciliates while only two genera have received 
the bulk of research attention, we have remained 
conservative. Following Lynn and Small (2002), 
we include three orders in this class and anxiously 
await data derived from silver staining, electron 
microscopy, and gene sequences on the distinctive-
ness of the aberrant genera included in this class. 
 The Order Synhymeniida includes forms whose 
ciliary fringe or synhymenium is composed of 
dikinetids or small polykinetids, typically of 4–6 
kinetosomes. The synhymenium extends from the 
right postoral body surface sometimes onto the 
left dorsal body surface. We include four families: 
 Nassulopsidae , Orthodonellidae , Scaphidiodont-
idae , and Synhymeniidae . Deroux, Iftode, and Fryd 
(1974) and Deroux (1978) laid the modern ground-
work for this group, based on Jankowski (1968a). 
Sola et al. (1990a) have speculated that Nassulopsis
might be removed from this order and placed in 
the Order Nassulida . We await gene sequence data 
before making this transfer. 
 The Order Nassulida includes taxa whose syn-
hymenium is composed of obvious polykinetids, 
restricted to the left ventral and sometimes dorsal 
surface. In some forms, these polykinetids have been 
reduced to three, which are restricted to the left side 
of the cytostome. Nevertheless, there is considerable 
Fig. 11.2. Stylized drawings of representative genera from the orders in the Class NASSOPHOREA . The microtho-
racids Pseudomicrothorax , Microthorax , and Discotricha
variation from this “typical” tripartite left oral pat-
tern: Enneameron (formerly Nassula brunnea ; see 
Jankowski, 1968a) may have more than five rows 
of monokinetids in an oral atrium (Fauré-Fremiet, 
1962a) while Parafurgasonia appears to have 
a paroral and a single oral polykinetid (Foissner 
& Adam, 1981). These variations have led some 
to elevate included families and genera to ordinal 
rank (e.g., Deroux, 1994b; Grain, Peck, Didier, 
& Rodrigues de Santa Rosa, 1976; de Puytorac, 
1994a). We include conservatively three families: 
 Furgasoniidae , Nassulidae , and Paranassulidae . 
 The third order, the Microthoracida , includes 
typically small ciliates with sparse somatic ciliation
and a cyrtos that is reduced in size. Although three 
 adoral polykinetids are typical, there is consider-
able variation among genera (e.g., Foissner, 1985a). 
 Fibrous trichocysts with anchor-like tips are con-
sidered characteristic of the order. We include 
three families in the order: Leptopharyngidae , 
 Microthoracidae , and Discotrichidae . Members of 
the latter family, which is monotypic, are highly 
aberrant: Discotricha has a non-ciliated dorsal 
surface, ventral somatic polykinetids that are cirrus-
like, and extrusomes that do not have anchor-like 
tips (Foissner, 1997a; Tuffrau, 1954; Wicklow 
& Borror, 1977). Gene sequence data are clearly 
needed here! 
 We place one family incertae sedis in this class. 
We have removed the Colpodidiidae from the 
Order Nassulida , where it was placed by Lynn and 
Small (2002), as these species lack a cyrtos and 
have highly aberrant oral ciliature, and placed it 
incertae sedis in the Class NASSOPHOREA . 
 11.2 Life History and Ecology 
 Nassophoreans are only rarely observed in high 
abundances. Most species are found in freshwaters 
or soils with fewer in brackish and marine habitats. 
However, they have been found on all continents. 
 Microthoracids are typical of soils in Europe 
(Foissner, 1981a, 1998a) and Africa (Buitkamp, 
1977; Foissner, 1998a, 1999a). Nassulids and 
 synhymeniids have been described from marine 
and freshwaters in Europe (Agamaliev, 1967; 
Alekperov, 1984; Burkovsky, 1970; Czapik & 
Jordan, 1976; Finlay & Maberly, 2000), Africa 
(Dragesco, 1965; Njiné, 1979), Asia (Ozaki & 
Yagiu, 1941; Song & Wei, 1998), North America 
(Borror, 1972; Bullington, 1940), and Antarctica 
(Thompson, 1972). 
 The larger nassulids and microthoracids 
appear to feed preferentially on cyanobacteria , 
such as Anabaena , Aphanizomenon , Oscillatoria , 
Phormidium , and Synechococcus (Canter, Heaney, 
& Lund, 1990; Peck, 1985; Tucker, 1978). They 
do show some feeding preferences : Nassula aurea
was reported never to graze Gomphosphaeria
and Microcystis (Canter et al., 1990) while 
Pseudomicrothorax dubius rarely ingested some 
Anabaena species (Peck, 1985). Both surface 
charges and phagocytosis-specific molecules on 
the cyanobacterial filaments are necessary to 
explain these feeding preferences (Kiersnowska, 
Peck, & de Haller, 1988). Feeding behavior of 
Pseudomicrothorax has been divided into two 
phases: (1) a contact swimming phase during 
which the ciliate guides itself along the cyano-
bacterial filament , typically finding an end to 
begin ingestion; and (2) a phagocytosis phase that 
involves first attachment and then ingestion. Ca 2+
influx is probably essential for both the attach-
ment phase of phagocytosis and for the exocytosis 
of lysosomes during the initial ingestion of the 
filaments (Peck & Duborgel, 1985). Some slightly 
starved Nassula species show a negative photo-
taxis to light when they also possess a conspicuous 
stigma-like structure. How this phototaxis is medi-
ated has not been determined although its function 
is presumed to lead these ciliates towards slightly 
illuminated regions that are preferred by cyano-
bacteria (Kuhlmann & Hemmersbach-Krause, 
1993b). Microthoracids are typically bacteri vorous 
(Foissner, Berger, & Kohmann, 1994) and have 
been reported from the activated sludge biotope 
(Leitner & Foissner, 1997a). 
 Deroux (1994b) remarked that many nassopho-
reans harbor Chlorella symbionts. However, there 
has been little research on this relationship. 
 Nassophoreans are likely eaten by a variety 
of invertebrates, but records of this are scarce. 
Addicot (1974) implied that Leptopharynx might be 
eaten by mosquito larvae while Braband, Faafeng, 
Källqvist, and Nilssen (1983) observed fish fry 
and copepods to feed on Nassula . The suctorians , 
Podophrya (Canter et al., 1990; Fauré-Fremiet, 
1945) and Sphaerophrya (Clément-Iftode, 1967), 
are repeatedly observed as predators of nassulids . 
11.2 Life History and Ecology 237
 Encystment is typical of nassophoreans , which 
are stimulated to do so by the lack of food (Beers, 
1966a; Canter et al., 1990; Mulisch & Hausmann, 
1989). The cyst wall is composed of three layers 
with the mesocyst layer having chitin microfibrils, 
as has also been observed in heterotrichs (Mulisch 
& Hausmann, 1989). 
 11.3 Somatic Structures 
 Synhymeniids and nassulids are typically larger 
ciliates, holotrichously ciliated with cylindrical 
bodies. Microthoracids are smaller, often flattened, 
and with fewer somatic kineties whose kinetosomes 
may be more widely dispersed or even aggregated 
into polykinetid-like

Crie agora seu perfil grátis para visualizar sem restrições.