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1984 
 – Longitricha Gajewskaja, 1933 
 – Rhagadostoma Kahl, 1926 
 – Urotricha Claparède & Lachmann, 1859 
Incertae sedis in Class PROSTOMATEA 
 – Amphibothrella Grandori & Grandori, 1934 
 – Peridion Vuxanovici, 1962 
 – Peridionella Vuxanovici, 1963 
Incertae sedis in Class PROSTOMATEA 
 Family MALACOPHRYIDAE Foissner, 1980 
 Size, small; shape, ovoid; free-swimming; alve-
oli, regularly patterned, almost quadrangular ; 
somatic ciliation, holotrichous, with kinetids of 
bipolar kineties disposed in paratenes, and poste-
rior partially non-ciliated; caudal cilia, present; oral 
region, subapical; oral dikinetid along right side of 
oral area; two elongate “brosse” units along left 
side of oral area, similar (?) to oral polykinetids 
of oligohymenophoreans ; cyrtos with fine nema-
todesmata; macronucleus, globular; micronucleus, 
present; contractile vacuole, present; cytoproct (?); 
feeding (?); in terrestrial habitats; one genus. 
NOTE : Deroux (1994) placed this family as incer-
tae sedis in the Subclass Nassulia . We are placing it 
here for two reasons: the development of parateny, a 
feature characteristic of the prostomes; and a presump-
tion that its oral polykinetids are homologous to “bro-
sse” units. However, this placement must be confirmed 
by ultrastructural study and molecular genetic data. 
 – Malacophrys Kahl, 1926 
17.3 The Ciliate Taxa to Genus 409
Class PLAGIOPYLEA Small & Lynn, 1985
(syns. Contofragmea, Contofragmina p.p., 
Plagiopylia, Spirotrichophora p.p.)
Size, small to large; shape, variable, but often 
flattened; free- swimming; alveoli, well-developed, 
often filled with dense material; somatic ciliation, 
holotrichous, very dense in large forms, but extremely 
reduced in smaller forms; somatic monokinetid with 
divergent postciliary ribbon, well-developed anteri-
orly-directed kinetodesmal fibril, and a transverse 
ribbon arising from dense material near triplets 2 and 
3, extending laterally in Trimyemidae and anteriorly 
at least in Plagiopylidae, but if odontostomatids are 
correctly placed here, they typically have dikinetids; 
somatic extrusomes as mucocysts, which may be 
elongate and rod-shaped; oral region, variable, from 
subapical to post-equatorial, may be deeply invagi-
nated; cytostome partially encircled by one or two 
files of dikinetids (?), but if odontostomatids are 
correctly placed here, oral ciliature can include 
polykinetids; stomatogenesis, holotelokinetal, but 
may be apokinetal in odontostomatids (?); macronu-
cleus, homomerous; conjugation, temporary; mito-
chondria may be replaced by hydrogenosomes, 
which in many species are associated with endo-
symbiotic methanogens; bacterivorous and algivo-
rous; in marine and freshwater habitats, especially 
common in anaerobic salt-marsh and interstitial 
biotopes, and sometimes as endocommensals in the 
digestive tracts of echinoids and hippopotami; one 
orders and one order incertae sedis.
NOTE: Lynn (2004) characterized this class as 
a “riboclass” because there is strong support from 
small subunit rRNA gene sequences for uniting 
the included families, but no strong morphologi-
cal synapomorphies. Ultrastructural observations 
(Lynn, 1991) reveal circumcytostomal dikinetid 
units at the base of the oral cavity of plagiopylids. 
Research is needed to confirm these as homologues 
of the trimyemid oral dikinetids. Stoeck et al. (2007) 
have demonstrated that the odontostomatid genus 
Epalxella strongly associates with trimyemids and 
plagiopylids, providing preliminary support for our 
transfer of the Order Odontostomatida to this class.
Order Plagiopylida Jankowski, 1978
(syn. Perikinetida, Trimyemida p.p.)
Size, small to large; typically with sandwich-like 
arrangement of the hydrogenosome-methanogen 
assemblages; three families.
Family PLAGIOPYLIDAE Schewiakoff, 1896
(syn. Paraplagiopylida, Paraplagiopylidae)
Size, small to medium; shape, somewhat 
bean-shaped, flattened, with oral region at 
indented part; free-swimming; somatic cilia-
tion, holotrichous, dense, with somatic kine-
ties extending from dorsal surface over the 
anterior end to terminate on the oral region;
with striated band on right surface arising near 
right margin of oral cavity; oral cavity, deep, 
transverse, opening ventrally with a more 
internal tubular part preceding the cyto-
stome; oral ciliature as extensions of somatic 
kineties, more densely packed with kineto-
somes, lining the tubular part and terminating at 
the cytostome; macronucleus, globular to ellip-
soid; micronucleus, present; contractile vacuole, 
present; cytoproct (?); feeding on bacteria and 
cyanobacteria; in marine, brackish, and fresh-
water habitats, particularly anaerobic biotopes 
with several species endocommensal in the 
digestive tracts of sea urchins and hippopotami; 
four genera.
– Lechriopyla Lynch, 1930
– Paraplagiopyla Thurston & Grain, 1971
– Plagiopyla Stein, 1860
– Pseudoplagiopyla Small & Lynn, 1985
Family SONDERIIDAE Small & Lynn, 1985
(syn. Parasonderiidae)
Size, small to large; shape, ovoid, some-
what flattened dorsoventrally; free-swimming; 
somatic ciliation, holotrichous, dense; with stri-
ated band on right surface arising near right 
margin of oral cavity; oral cavity flattened, 
conical, deep, opening apically to subapically;
oral ciliature as extensions of somatic kineties, 
with densely packed kinetids, lining surfaces 
of cavity; macronucleus, globular to ellipsoid; 
micronucleus, present; contractile vacuole, 
present; cytoproct, present; feeding on bacteria, 
cyanobacteria, and microalgae, such as diatoms; 
in marine and brackish water habitats, rarely 
freshwater; four genera.
– Oncosonderia Jankowski, 1980
– Parasonderia Jankowski, 2007
– Sonderia Kahl, 1928
– Sonderiella Kahl, 1928
410 17. The Ciliate Taxa Including Families and Genera
Family TRIMYEMIDAE Kahl, 1933
(syn. Sciadostom[at]idea)
Size, small; shape, ovoid, tapered at both ends; 
free-swimming; somatic ciliation, holotrichous, 
but kineties with kinetosomes much reduced in 
numbers, appearing as several spirals around 
body; caudal cilium, prominent; without striated 
band; oral cavity, a shallow depression, opening 
to the right; oral ciliature as two semicircular 
files of dikinetids on the left and several (2–4) 
dikinetid units at the right anterior end of 
the semicircular files; macronucleus, globu-
lar; micronucleus, present; contractile vacuole, 
present; cytoproct (?); bacterivorous; in marine 
and freshwater anaerobic habitats, sometimes 
occurring as endocommensals in the intestines of 
echinoids; one genus.
– Trimyema Lackey, 1925
Incertae sedis in Class PLAGIOPYLEA 
 Order Odontostomatida Sawaya, 1940 
 (for Ctenostomata , Ctenostom[at]ida , Ctenosto-
mina ; syn. Odontostomata ) 
 Size, small; shape, discoid, laterally com-
pressed, wedge- or helmet-shaped, typically 
nearly as wide as long, with armour-like 
cuirass and often short posterior spines ; 
somatic ciliature, reduced, typically as dikinetids 
or occasionally cirrus-like, with somatic kine-
ties often separated into anterior and posterior 
segments; oral polykinetids, inconspicuous, 
typically <10 in number ; paroral, sometimes 
present, typically inconspicuous; stomatogene-
sis, possibly apokinetal; macronucleus, globular, 
one to several; cytoproct, absent; feeding (?); in 
marine, brackish, and freshwater anaerobic habi-
tats; three families. 
NOTE : The Order Odontostomatida with its 
three included families is tentatively transferred 
to the Class PLAGIOPYLEA based only on the 
results of the small subunit rRNA gene sequence 
of Epalxella , which is unambiguously associated 
with plagiopylids and trimyemids (Stoeck et al., 
2007). It will be necessary to at least obtain gene 
sequences of representatives of the other two fami-
lies to resolve this uncertainty. 
 Family DISCOMORPHELLIDAE Corliss, 1960 
 (for Discomorphidae [for Ctenostom [at] idae ]) 
 Size, small; shape, discoidal, laterally

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