Logo Passei Direto

A maior rede de estudos do Brasil

48 pág.
Cap 15

Pré-visualização | Página 5 de 25

(1966a, 1966c, 1973c) suggested the division into 
three major groups, now recognized as orders: 
the Apostomatida , the Astomatophorida , and the 
 Pilisuctorida . The Order Apostomatida is char-
acterized by a highly modified “hymenostome” 
oral ciliature accompanied by a rosette and its 
associated x , y , and z kineties; there are three fami-
lies – the Colliniidae , the Cyrtocaryidae , and the 
 Foettingeriidae . Description of the complete life 
cycle of members of the Order Astomatophorida , 
monotypic for the Family Opalinopsidae , may 
confirm placement of these curious parasites of the 
internal organs of cephalopods , characterized by 
division by catenulation . The Order Pilisuctorida 
includes species that spend most of their life 
cycle attached to the cuticular setae of crusta-
ceans (Bradbury, 1975; Mayén-Estrada & Aladro-
Lubel, 2004). Bradbury (1982) has confirmed 
Jankowski’s (1966a) hypothesis that the pilis-
uctorid Conidophrys has a rosette opening in its 
 tomite stage, and so is legitimately an apostome . 
Bradbury (1989) has interpreted the features of 
the fine structure of the exuviotrophic apostome 
Hyalophysa as homologous to the paroral (i.e., 
two rows of staggered barren kinetosomes) of 
 hymenostomes , an interpretation corroborated by 
gene sequence data (J.C. Clamp et al., unpublished 
data 2008). 
 The peritrichs have long been presumed to have 
derived from a pleuronematine - or thigmotrich -
like scuticociliate (Fauré-Fremiet, 1910, 1950a; 
Lom, Corliss, & Noirot-Timothée, 1968). The ante-
rior thigmotactic region of these putative ances-
tors has been presumed to have given rise to the 
attachment structures – the scopula and adhesive 
disk – of the peritrichs , while the posterior oral 
ciliature was presumed to have evolved into the 
prominent peristomial ciliature of the Subclass 
 Peritrichia . This oral ciliature is composed of a 
paroral, called the haplokinety , accompanied by 
oral polykinetid 1 – both encircle the apical end in a 
counterclockwise sense before entering into the oral 
cavity, called an infundibulum in this group. These 
oral organellar complexes are accompanied by two 
other oral polykinetids that appear peniculus -like in 
that they are oriented lengthwise in the oral cavity. 
Sequences of the SSUrRNA genes have confirmed 
the monophyly of the sessilid peritrichs . Moreover, 
SSUrRNA gene sequences place hymenostomes and 
 peritrichs as sister lineages, refuting the “classical” 
hypothesis that peritrichs share a close common 
ancestry with the scuticociliates (Itabashi, Mikami, 
Fang, & Asai, 2002; Miao, Yu, & Shen, 2001; Miao 
et al., 2004b). However, these same gene sequences 
suggest that sessilids and mobilids may not be sister 
taxa (Gong, Yu, Villalobo, Zhu, & Miao, 2006)! 
 Monographic works on the peritrichs focus on 
the two major orders: (1) those that deal primarily 
with the sessiline forms, those peritrichs attached 
to substrates, both living and non-living, by the 
 scopula or scopular products; and (2) those that 
deal with the mobiline forms, peritrichs that attach 
temporarily by means of an adhesive disk supported
by a skeletal apparatus and surrounded by three 
 ciliated girdles (Lom, 1994). Sessiline peritrichs 
can be solitary or colonial. Solitary species often 
aggregate, settling very close to each other to 
form so-called pseudocolonies . True colonial forms 
remain attached to the same stalk after cell division, 
and if zooids differentiate a monomorphic colony 
becomes polymorphic . The monographs on ses-
silines by Kahl (1935), Nenninger (1948), Stiller 
(1971), and Guhl (1979), for example, still remain 
useful. Foissner and Schiffmann (1975, 1976) have 
demonstrated that silver-staining can provide a 
rich set of characters to supplement those of cell 
size and shape, which were traditionally used to 
separate species. These surface structures can also 
be revealed by SEM when the peritrichs are relaxed 
by chlorbutol (Carey & Warren, 1983). This focus 
on surface features has lead to the revision of previ-
ous descriptions and the recognition of new genera 
(e.g., see Foissner & Schiffmann, 1976; Leitner 
& Foissner, 1997b; Warren, 1986, 1987, 1988). 
Roberts, Warren, and Curds (1983) have also dem-
onstrated that multivariate and Fourier analyses of 
the outline shape of Vorticella species can resolve 
taxa to some degree. Sequencing of ITS regions 
has suggested that river-dwelling populations of 
Carchesium polypinum may show some vicari-
ance biogeography (Miao et al., 2004a) while gene 
flow among lake-dwelling populations appears to 
be much higher when assessed using inter-sample 
sequence repeat (ISSR) fingerprinting (Zhang, 
Yang, Yu, Shu, & Shen, 2006). Clearly, these two 
studies only scratch the surface of the population 
genetics and biogeography of the peritrichs . Some 
 sessiline groups secrete a lorica , which may be 
directly attached to the substrate or which may 
surround the zooid that is itself attached to the 
substrate by the scopula . Features of the lorica , 
such as its shape, character of the opening, and 
 presence of an operculum , have proved useful in 
 discriminating genera and species within genera 
(e.g., see Clamp, 1987, 1991; Finley & Bacon, 
1965; Jankowski, 1985, 1986). The preliminary phy-
logenetic analyses based on SSUrRNA suggest that 
family assignments of sessilids based on morphology 
may not be correct. Nevertheless, we have remained 
conservative in our treatment and recognized 
the following 14 families in the Order Sessilida : the 
 Astylozoidae , the Ellobiophryidae , the Epistylididae , 
the Lagenophryidae , the Operculariidae , the 
 Ophrydiidae , the Opisthonectidae , the Rovinjel-
lidae , the Scyphidiidae , the Termitophryidae , the 
 Usconophryidae , the Vaginicolidae , the Vorticelli–
dae , and the Zoothamniidae . 
 The Order Mobilida is characterized by a mobile 
 zooid as a “ permanent telotroch ” or swarmer stage, 
which has a complex, ring-like, skeletal armature 
of denticles and fibres that support the adhesive 
disk on the aboral pole. We include the following 
five families: the Leiotrochidae , the Polycyclidae , 
the Trichodinidae , the Trichodinopsidae , and the 
 Urceolariidae . Monographs on mobilines includes 
the work of Wallengren (1897), Haider (1964), 
Raabe (1964), and Lom (1994). Others continue to 
record the morphological variability of trichodinids
using numbers and sizes of the skeletal denticles , as 
well as other denticle characters (Kazubski, 1981, 
1988, 1991; Van As & Basson, 1989). Denticle 
characters have been used to assess the phylogeny 
with the Family Trichodinidae and demonstrate 
that Hemitrichodina is a very divergent genus 
(Gong, Yu, Feng, & Shen, 2005). 
 The astomes , now as the Subclass Astomatia , 
have always presented a problem to ciliate sys-
tematists who have relied on oral characters 
to determine affinities. These endosymbionts, 
typically of annelids , are all mouthless, but have 
evolved elaborate holdfast structures in the form 
of hooks, spines, spicules, and suckers . The group 
may be polyphyletic as astomy has arisen inde-
pendently within the hymenostomes (Kozloff, 
1954), and astomatous mutants of Tetrahymena
and Glaucoma have been isolated in the labora-
tory (Frankel, 1961; Orias & Pollock, 1975; 
Rasmussen & Orias, 1975). Nevertheless, the cur-
rent phylogenetic hypothesis is that astomes arose 
from a thigmotrich -like ancestor with a reduced, 
posterior oral apparatus and an anterior thigmotac-
tic zone (de Puytorac, 1954; de Puytorac, Grolière, 
& Grain, 1979). In our scheme, and different 
from de Puytorac (1994g), the subclass includes 
the single Order Astomatida with its nine fami-
lies: the Anoplophryidae , the Buetschliellidae , 
the Clausilocolidae , the Contophryidae , the Hapto-