Thigmokeronopsis magna, 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 : 956-958

Thigmokeronopsis magna nov. spec.

( Figures 9 , 15J–M, O ; Table VII)

Diagnosis

Large flexible marine Thigmokeronopsis about 150–300650–80 M m in vivo; ca 65 adoral membranelles extending to about one-third of cell length; 12–16 left postoral cirral rows forming thigmotactic field; 60 left and 70 right marginal cirri, about 43 and 15 pairs of cirri in midventral and frontal rows, respectively; one buccal, ten transverse and two frontoterminal cirri; three dorsal kineties; no caudal cirri; more than 150 macronuclear nodules; one contractile vacuole positioned in about mid-body.

Description

Size mostly about 200660 M m, body very flexible and variable in shape but generally slender and elongate, with anterior part distinctly narrower than posterior; anteriorly narrowly rounded, posteriorly tapered; buccal field wide, about 30% of cell length ( Figure 9A ). Pellicle thin, no cortical granules observed although cytoplasm usually brownish to dark brown in colour (due to food?) as observed under low magnifications. Cytoplasm with many tiny lipid droplets and food vacuoles containing mainly small and large pennate diatoms or small protozoans. Contractile vacuole on left of body and near equatorial level ( Figure 9A, H ). More than 150 macronuclear nodules scattered throughout the cell ( Figure 9F ), spherical to ellipsoid, usually with one to several large nucleoli ( Figure 9G ).

Movement slow, usually three different modes observed: (1) crawling on bottom of Petri dish or debris, making small circular movement ( Figure 9I ); (2) attached by thigmotactic field to the bottom while the raised anterior part of body makes (slow) left–right movements ( Figure 9J ); or (3) when disturbed, relatively faster, crawling around irregularly. When swimming in water, moves slowly with no special features ( Figure 9B ).

Buccal field large and deep. Adoral zone of membranelles extending far on to right side. Paroral and endoral membranes about equal in length, slightly bent in posterior portion, optically appearing to intersect ( Figure 9K ). One buccal cirrus at about mid-level of undulating membranes.

About 15 frontal cirri forming bicorona, which are not clearly distinguished from the midventral cirri posteriorly although the anterior-most (usually three) cirri are conspicuously enlarged ( Figure 9K ). Two midventral rows distinctly separated (so that the cirri are not arranged in typical zig-zag pattern), terminating near posterior rightmost transverse cirri ( Figure 9E, K ). Left postoral cirral field (5thigmotactic field) consisting of about 13 (in maximum width) densely packed longitudinal rows, in each of which the cirri are basically loosely arranged ( Figure 15K ). Bases of cirri in this thigmotactic field mostly smaller than other ‘‘normal’’ ones and more or less ovoid in shape ( Figures 9K , 15K ). Transverse cirri slightly enlarged and arranged in J-shape, joining thigmotactic field ( Figures 9D, E , 15L ). Marginal rows not confluent posteriorly. Dorsal kineties constantly three in number, densely ciliated (ca 3 M m long, Figure 15J ); without caudal cirri.

Remarks

Till now, four species within the genus Thigmokeronopsis have been described: T. jahodai , T. antarctica , T. rubra , and T. crystallis ( Wicklow 1981; Petz; Hu et al. 2004). Thigmokeronopsis antarctica is separated from the new species by having several buccal cirri, shortened midventral rows, only one thigmotactic cirral row and no transverse cirri. Thigmokeronopsis magna differs from T. crystallis in possessing many more cirral rows in the thigmotactic field (12–16 versus 4–7) ( Wicklow 1981; Petz 1995).

The new species is distinguished from the type species, Thigmokeronopsis jahodai Wicklow, 1981 , in that it has: (1) three dorsal kineties (versus four in T. jahodai ); (2) one buccal cirus (versus two in T. jahodai ); (3) more cirri in the midventral rows (ca 100 versus 50) ( Wicklow 1981).

Thigmokeronopsis rubra Hu et al., 2004 is a colourful (brick-red) species with two kinds of distinct cortical granules and thus can be clearly separated from T. magna . In addition, the former possesses fewer adoral membranelles (33–43 versus ca 65) and fewer thigmotactic cirral rows (7–11 versus 12–16) ( Hu et al. 2004).

Figures

Figure 9. Thigmokeronopsis magna nov. spec. from life (A, B, H–J) and after protargol impregnation (C–G, K). (A) A typical specimen, ventral view; (B) schematic, to show the pattern of movement when swimming; (C) four pairs of midventral cirri, to demonstrate the fibre system associated with the cirri; (D) details, to show transverse (arrow) and thigmotactic cirri (arrowhead); (E) ventral view, arrows mark the thigmotactic area; (F) dorsal view of the same cell as in (E), to show the distribution of macronuclei, arrows mark the dorsal kineties; (G) several macronuclear nodules; (H) two different body forms, arrow points to the contractile vacuole; (I) diagram showing the pattern of movement while on the bottom; (J) the third type of movement: cells firmly attached to the bottom, arrows mark the thigmotactic area; (K) anterior portion of ventral side, arrowhead marks the paroral membrane, double-arrowheads indicate the endoral membrane, arrow points to the frontoterminal cirri. Scale bars: 100 Mm (A); 50 Mm (E, F); 150 Mm (H); 40 Mm (K).

Figure 15. Photomicrographs of (A–I, N) Metaurostylopsis rubra, (P) Holosticha sp. and (J–M, O) Thigmokeronopsis magna nov spec. after protargol impregnation. (A) Ventral view of anterior portion in late divisional stage; (B) to show the macronuclei in replication stage (arrow marks the replication band); (C, D) detailed portion of the opisthe, black arrows in (C) and (D) indicate the fronto-terminal cirri; white arrow in (D) points to the ventral row; (E, F) buccal field, white arrow in (E) marks the fronto-terminal row, while double-arrowheads indicate the buccal cirrus; black arrow in (F) points to the long fronto-terminal row; (G, H) ventral view of proter, arrow in (G) marks the fronto-terminal cirral row; (I) ventral view, to show the general pattern of ventral, marginal and transverse cirri; (J) portion of dorsal side, to show the dorsal kineties (arrowheads); (K) ventral view, to show the thigmotactic area, note that the cirri are densely but irregularly arranged (arrows); (L) ventral view of caudal part, arrow indicates the transverse cirri; (M) ventral view of buccal region, white arrow indicates the two fronto-terminal cirri, whereas the black one marks the distal end of adoral zone of membranelles; (N) ventral view in a late divider, to show the newly formed transverse cirri (arrows); (O) to show the fibres connecting to the marginal cirri; (P) dorsal view, to show the large extrusomes (arrowheads).