Amphisiella antarctica, 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 : 969-970

Amphisiella antarctica nov. spec.

( Figures 11E–K , 16A–F ; Table VIII)

Diagnosis

Slender marine Amphisiella 120–200630–50 M m in vivo with narrowed caudal portion. Eight to twelve frontal and five transverse cirri; single ventral row extending to posterior third of cell length with about 29 cirri on average; two small ventral cirri close to transverse cirri; 25–32 adoral membranelles; 39–56 left and 42–55 right marginal cirri; four dorsal kineties and four caudal cirri; two macro- and two micronuclei. Cortical granules large and sparsely distributed on dorsal side.

Description

In vivo mostly about 160640 M m in size. Cells flexible, slightly contractile and often more or less distorted in middle portion (even twisted while gliding on debris, Figure 11H ); dorsoventrally flattened by about two-thirds. Body shape distinctly slender with posterior portion distinctly narrowed; ratio of cell length to width about four to one ( Figure 11E ), buccal field narrow and inconspicuous, about one-quarter of body length; cell margins generally parallel but often curved outward in middle portion. Dorsal side slightly uneven, irregularly bulging ( Figure 11G ).

Pellicle soft and thin; ‘‘cortical granules’’ colourless and large (about 1 M m), not grouped and sparsely distributed on dorsal side ( Figure 11F ). Cytoplasm greyish or colourless, often containing numerous light-reflecting globules (2–5 M m across), which render the cell dark under low magnification. Contractile vacuole not observed. Food vacuoles several to many, always containing small diatoms or flagellates ( Figure 11E ). Two elongate macronuclei, ca 20615 M m in size in vivo, slightly separated from one another near left side of body; constantly two large (4–5 M m across), globular micronuclei, adjacent to macronuclei ( Figures 11K , 16B ).

Movement relatively slow, crawling without pause on debris. When swimming, spirally rotating about the longitudinal axis.

Buccal apparatus as shown in Figure 11I . Adoral zone of membranelles (AZM) extending to about 25% of cell length, longest base of membranelles about 7 M m long; distal end of AZM bending only slightly posteriad at right. Paroral membrane two-rowed, parallel to zig-zagging endoral membranes. Along undulating membranes always some densely packed argentophilic granules (extrusomes?) recognizable ( Figure 11J , arrowheads). Pharyngeal fibres conspicuous after protargol impregnation, about 30 M m long ( Figure 11I ).

Four enlarged frontal cirri followed by usually five smaller ones posteriorly; single ventral row consisting of 21–36 cirri extends to about posterior third of cell length. Always two small cirri anterior to five enlarged transverse cirri, which are positioned almost completely at posterior end of cell ( Figure 11J ) and are connected by five fibres about 40 M m long. The two marginal rows are widely separated posteriorly and terminate near transverse cirri ( Figure 11J ).

Four dorsal kineties loosely ciliated, cilia about 5 M m long, comprising ca 10 pairs of basal bodies each. Four caudal cirri at margin of cell ( Figure 11K ).

Remarks

Considering the body shape, size, habitat and general appearance, at least two marine morphotypes should be compared with the new species described here: Amphisiella thiophaga (Kahl, 1928) Kahl, 1932 and A. annulata (Kahl, 1928) Kahl, 1932 . The new species differs from the former in having a narrowed caudal portion (versus broadly rounded in A. thiophaga ) and a relatively shorter ventral row of cirri that terminates far away from the transverse cirri (versus extends completely to the transverse cirri) ( Kahl 1932).

Compared with A. annulata , the new species can be distinguished by body shape (with narrowed posterior end versus broadly rounded), lack of ring-like granules (‘‘Ringkugeln’’) in cytoplasm (versus present in the former species) and probably the presence of conspicuous cortical granules (versus absence?; none were mentioned in original description).

Figures

Figure 11. (A–D) Hemigastrostyla szaboi nov. spec. and (E–K) Amphisiella antarctica nov. spec. from life (A, E–H) and after protargol impregnation (B–D, I–K). (A) A typical specimen, arrow marks the groove, where the marginal cirri are positioned; (B) posterior portion of ventral side, arrow marks the two small ventral cirri, doublearrowheads indicate the transverse cirri, arrowhead points to the posterior end of right marginal row, note that there is a conspicuous gap between the transverse and right marginal cirri; (C) ventral view, arrow marks the undulating membranes, while the arrowhead indicates the position where the right marginal row and transverse cirri join together; (D) dorsal view, arrow indicates the anterior end of right marginal row, while arrowheads mark the caudal cirri; (E) ventral view of a typical individual; (F) dorsal view, to show the cortical granules; (G) lateral view, to demonstrate the flattened body shape; (H) to show the flexible body; (I) anterior portion of ventral side, arrowhead indicates the double-rowed paroral membrane, arrow marks the endoral membrane; (J) ventral view, arrowheads mark the extrusomes, which are positioned along undulating membranes, arrow indicates the posterior end of ventral row, while double-arrowheads mark the transverse cirri; (K) dorsal view, arrows mark the micronuclei, double-arrowhead indicates the caudal cirri. Scale bars: 50 Mm (A, C); 80 Mm (E); 30 Mm (I); 60 Mm (J, K).

Figure 16. Photomicrographs of (A–F) Amphisiella antarctica nov. spec. and (G–L) Hemigastrostyla szaboi nov. spec. after protargol impregnation. (A) Ventral view of buccal region, to show the ventral row (arrow); (B) macro- and micronuclei (arrows); (C, E) buccal area, to show the argentophilic granules along the undulating membranes (arrows and arrowheads); (D) caudal portion, to show the transverse and caudal cirri; (F) ventral view, arrow marks the micronucleus; (G) nuclear apparatus, arrows indicate the micronuclei; (H) to show the fibres associated with the marginal cirri; (I) ventral view of posterior cell end, to show the transverse cirri, note that there is no gap between right marginal row and the transverse cirri; (J) ventral view, to show the general appearance of infraciliature; (K) ventral view, to show a slender form, arrow indicates the distal end of adoral zone of membranelles; (L) ventral view of caudal region, arrow marks the transverse cirri.