Dysteria parovalis, Wilbert & Song, 2005

Wilbert, Norbert & Song, Weibo, 2005, New contributions to the marine benthic ciliates from the Antarctic area, including description of seven new species (Protozoa, Ciliophora), Journal of Natural History 39 (13), pp. 935-973 : 938-941

Dysteria parovalis nov. spec.

( Figures 2A–D ; Table III)

Diagnosis Marine oval Dysteria , in vivo 50–80640–60 M m; constantly with nine ventral kineties in

right field, of which three extend to anterior cell end; ca six to eight short fragments of

kineties in left equatorial field; oral ciliature consisting of three double-rowed fragments; macronucleus oval; three contractile vacuoles.

Etymology

Composite of par (similar to) and the species name ovalis , indicating that this species is similar to the well-known form Dysteria ovalis .

Description

Mostly about 70650 M m in vivo. Body bilaterally flattened by about 1:2–3. From side view, cell broadly oval and quadrilateral with posterior portion often slightly wider than anterior; apical end considerably truncated while posterior end obliquely truncated ( Figure 2A ). No furrows or ridges detected. Podite about 15 M m long, posteriorly positioned on narrow ventral side ( Figure 2B ). Cytoplasm colourless, containing numerous tiny granules but no food vacuoles recognizable. Cytostome ventrally positioned at anterior end, diagonally oriented, with inconspicuous nematodesmata (cytopharyngeal rods) extending dorsocaudally ( Figure 2D ). Three contractile vacuoles detected (to be confirmed as pulsation was not observed) two near dorsal margin, the third one near base of podite ( Figure 2A ). Macronucleus oval, about in mid-body, ca 25615 M m in vivo in size, characteristically dimorphic ( Figure 2D ).

Movement genus-typical, slowly crawling over substratum and slightly thigmotactic.

Infraciliature as shown in Figure 2D : when viewed from lateral aspect, ‘‘right’’ field of ciliature composed of nine densely spaced, slightly fragmented kineties of variable length, of which three extend to dorsal anterior end, while other six are shortened anteriorly ( Figure 2C ). To left of distal end of these kineties, one fragment of kineties is always present as a double-rowed structure. In mid-body, about six to eight short rows of densely packed basal bodies forming left equatorial field ( Figure 2C , arrow). Equatorial fragment consisting of about 10 basal bodies. One large argentophilic patch-like ‘‘gland’’ positioned subcaudally, about 10 M m in length, always present near the base of podite ( Figures 2C , double-arrowheads; 15J, arrows). Oral ciliature composed of three fragment-like kineties ( Figure 2D , arrow).

Remarks

The new species is characterized by the combination of the following criteria: broadly oval shape, without grooves or ridges, three contractile vacuoles (?), nine ventral kineties, large cell size and Antarctic habitat.

Till now, about 11 Dysteria species have been described using modern methods: D. calkinsi , D. ovalis , D. pusilla , D. cristata , D. armata , D. monostyla , D. antarctica , D. brasiliensis , D. procera , D. magna , and D. derouxi ( Deroux 1965, 1976). The former five species have considerably smaller size (usually smaller than 40 M m in length), fewer ventral kineties (three to six), thus can be clearly separated from D. parovalis ( Fauré-Fremiet 1965; Gong et al. 2002, 2003a, b, 2004; Song and Wilbert 2002).

Dysteria monostyla and D. antarctica can be identified by only five ventral kineties (versus nine in D. parovalis Petz et al. 1995 ; Gong et al. 2002). Dysteria brasiliensis can be recognized by the presence of the long caudal spine and also fewer ventral kineties (consistently five; Song and Packroff 1997).

Dysteria derouxi is large (75–110 M m long in vivo), has constantly eight ventral kineties (versus nine in D. parovalis ) and has two ventrally located contractile vacuoles (Gong and Song 2003b), hence easily separated from D. parovalis .

Compared with the new species described here: Dysteria procera can be identified by having only three ventral kineties (versus nine in D. parovalis ) ( Gong and Song 2003a); D. magna is an extremely large form (1506100 M m versus 50–80640–60 M m for D. parovalis ) with broadly rectangular body shape and constantly eight ventral kineties (versus nine in D. parovalis ) ( Gong and Song 2003a).

Figures

Figure 2. (A–D) Dysteria parovalis nov. spec. and (E–G) Orthodonella shenae from life (A, B) and after protargol impregnation (C–G). (A) Lateral view of a typical specimen; (B) ventral view, to show the flattened body shape; (C) somatic infraciliature, arrowheads mark the shortened ventral kineties; arrow indicates the fragment-like left kineties, while double-arrowheads mark the argentophilic structure; (D) left view, to show the general appearance of ciliature and nuclear apparatus; arrow marks the oral structure; double-arrowheads indicate the posterior end of cytopharyngeal fibres; arrowhead points to the terminal fragment; (E) ventral view, to show a cell full of large diatoms, arrow marks the synhymenium; (F) dorsal view, to show the pores of contractile vacuoles (arrows); (G) to demonstrate different sizes of cells after fixation. Scale bars: 50 Mm (A, E); 40 Mm (D); 70 Mm (G).