Strombidium apolatum, 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 : 953-955

Strombidium apolatum nov. spec.

( Figures 8 , 14A–I ; Table VI)

Diagnosis

Cordiform Strombidium in vivo about 50640 M m; ca 13 collar and seven buccal membranelles not continuous; girdle and ventral kinety with ca 45 and 60 basal body pairs, respectively; single elongate to sausage-like macronucleus; extrusomes evenly distributed along the somatic kineties; marine habitat.

Etymology

Composite of apo (derived from) and the species name latum , indicating that this species is different from the congener S. latum .

Description

Size about 40–60630–45 M m in vivo, after fixation ca 35–50 M m in length; cell ratios about 3:2 for length/width and ca 4:3 for dorsoventral flattening. Body shape consistently cordiform, often slightly asymmetrical when viewed ventrally; anteriorly broadly rounded, posteriorly slightly pointed ( Figure 8A ). Buccal cavity shallow, about one-quarter of cell length. Transparent subpellicular platelet layer in posterior three-quarters of cell ( Figure 8G , arrow), although the polygonal platelets often found in other congeners were not detected here. Equatorial girdle in anterior two-thirds length, ca 2 M m wide, immediately ahead of subpellicular platelet layer ( Figure 8H , arrow); extrusomes densely and uniformly distributed, inserting along girdle ( Figure 8D , arrows).

Cytoplasm tightly packed with dark globules (especially directly below the cell surface) and lipid droplets, rendering cells dark to almost black at low magnification. Macronucleus elongated to sausage-like (but sometimes irregularly shaped after fixation), about 25– 3067–10 M m in size, with many large nucleoli ( Figures 8H , 14D, H ). Micronucleus not detected.

Movement fast and almost without pause, hectically to and fro on the debris ( Figure 8C ).

Adoral zone spirally around peristomial field, cilia of most membranelles about 25– 30 M m long, always extending anteriorly ( Figure 8A ). Twelve to fourteen collar membranelles (CM), bases ca 7 M m in length and conspicuously longer than those in buccal zone. The buccal zone (BM) consists of six to eight membranelles and is positioned in the shallow buccal cavity, hence conspicuously separated from the CM ( Figure 8F ). Pharyngeal fibres highly developed, ca 20 M m long and extending obliquely to right side ( Figure 8F, G ).

Girdle kinety (equatorial kinety) composed of about 45 dikinetids (n 55), running along the edge of subpellicular platelet layer, begins at right margin, turns to dorsal side and then curves slightly towards the posterior (but clearly separated from the ventral kinety; Figure 8H , arrowhead). Ventral kinety more densely ciliated than girdle one, containing ca 60 basal body pairs, extending from right body margin subcaudally to the left and terminating laterally at posterior end of girdle kinety at level of about anterior third of cell length ( Figure 8H ). Cilia in girdle kinety about 2 M m long, while in ventral one ca 5 M m in length ( Figure 8G, H ).

Remarks

The genus Strombidium is a species-rich taxon containing more than 30 nominal species ( Kahl 1932; Maeda and Carey 1985; Lynn et al. 1988; Montagnes et al. 1988, 1990; Montagnes and Taylor 1994; Montagnes and Lynn 1991; Lynn and Gilron 1993; Petz et al. 1995). With respect to the subpellicular platelet layer which covers almost two-thirds of cell length, the flattened body shape, the shallow buccal cavity, densely arranged cilia in ventral kinety, the laterally positioned ventral kinety and the sausage-like macronucleus, this species clearly differs from all other known members of this genus ( Lynn et al. 1988; Montagnes et al. 1988, 1990; Montagnes and Lynn 1991; Petz et al. 1995; Song and Packroff 1997; Song et al. 2000).

Figures

Figure 8. Strombidium apolatum nov. spec. from life (A–C) and after protargol impregnation (D–I). (A) Ventral view of a typical specimen; (B) to show a cell attached to the bottom; (C) pattern of movement; (D) dorsal view, to show the arrangement of extrusomes (arrows); (E) ventral–lateral view, to show the girdle and ventral kinety, which almost meet at equatorial area (arrow and arrowhead, respectively); (F) anterior portion of ventral view, to show the buccal structure: arrow marks the paroral membrane, double-arrowheads indicate the buccal membranelles, arrowheads point to the collar membranelles; note the highly developed cytopharyngeal fibres extending backwards; (G) ventral view, arrow marks the subpellicular platelet layer; (H) dorsal view, arrow marks the equatorial girdle, arrowhead points to the gap between girdle and ventral kinety; (I) an individual in early divisional stage, double-arrowheads mark the newly formed collar membranelles, while arrow indicates the buccal ones; note the paroral membrane (arrowhead). Scale bar: 30 Mm.

Figure 14. Photomicrographs of (A–I) Strombidium apolatum nov. spec. and (J–N) Heterostentor shenae after protargol impregnation. (A) Dorsal view, to show the gap between the equatorial and ventral kinety (arrow); (B) dorsal view, black arrow marks the macronucleus, whereas the white one indicates the end of ventral kinety; (C) ventral view, white and black arrows point to the kinety-gap and macronucleus, respectively; (D, H) macronucleus; (E) dorsal view, to show the equatorial kinety and the girdle (arrows); (F) ventral view, arrowheads mark the inconspicuous buccal membranelles, whereas the arrow points to the cytopharynx; (G) ventral view, focusing at surface level, arrow indicates the newly formed oral primordium, arrowheads mark the equatorial kinety; (I) ventral view, to show the girdle (black arrows) and the equatorial kinety (white arrows); (J) dorsal side of anterior portion, to show the adoral zone of membranelles; (K, M) ventral view, arrow indicates the proximal end of adoral zone of membranelles, while the arrowheads in (K) mark the suture, where some kineties are shortened; (L) to show some irregularly arranged membranelles (arrows); (N) caudal view, to show the thigmotactic area, where the basal bodies are densely arranged (arrows).