Aponotohymena isoaustralis, Gupta & Abraham & Somasundaram & Toteja & Makhija & El-Serehy, 2017

Gupta, Renu, Abraham, Jeeva Susan, Somasundaram, Sripoorna, Toteja, Ravi, Makhija, Seema & El-Serehy, Hamed A., 2017, Taxonomic and Morphogenetic Description of the Freshwater Ciliate Aponotohymena isoaustralis n. sp. (Ciliophora; Oxytrichidae) Isolated from Sanjay Lake, Delhi, India, Acta Protozoologica 56 (2), pp. 93-107 : 94-97

Morphology of Aponotohymena isoaustralis n. sp.

Live cell: Average body size in vivo 148 × 46 µm (n = 25), length: width ratio 4:1, elongated body; dorsoventrally flattened about 2:1, flexible, colourless cytoplasm with a greenish appearance at the margins when observed at low magnifications. Yellowish green cortical granules about 0.8 µm in diameter aligned along the margins and irregularly distributed throughout the cell; they may also be randomly concentrated as clusters along the left margin and posterior end of the cell. Single contractile vacuole about 15 µm in diameter located below the AZM near the left margin. Cell division eve- ry 11 h. Encystment generally takes place within 24 h of starvation; the average diameter of the resting cyst in life is 64.53 µm (n = 12) with smooth ectocyst covered with mucus layer and granulated cytoplasm ( Fig 1A, B, E–H, J, K ).

Nuclear morphology: Two macronuclear nodules each about 20 × 14 µm in size (in protargol preparations), spherical to ellipsoidal, located along the cell mid line, one about 19 µm away from the anteriormost part and the other about 16 µm away from the posterior- most part of the cell; distance between the two macronuclei is about 22.2 µm; micronucleus absent ( Fig. 1N ).

Infraciliature characteristics: Adoral zone of membranelles (AZM) occupies about 34% of the body length in protargol preparations and is composed of 32– 40 membranelles. Undulating membrane (UM) with a characteristic hook at the distal end ( Notohymena - pattern); 18 FVT cirri with 3 frontal cirri, 4 frontoventral cirri, 1 buccal cirrus, 3 postoral ventral cirri, 2 pretransverse ventral cirri and 5 transverse cirri; transverse cirri equidistant to each other and usually arranged in a pseudo row. IV/2 and V/4 are closely placed whereas V/3 is distantly placed (distance between IV/2 and V/4 is 3.10 µm and between V/4 and V/3 is 5.14 µm). Marginal rows are separated (nonconfluent) posteriorly with about 30–38 cirri in right and left marginal row ( Figs 1C, L , 2A ; Table 1).

The dorsal ciliature is of typical oxytrichid pattern with 4 dorsal kineties (DK 1–4) and 2 dorsomarginal rows (DM 1,2). Three dorsal kineties (DK 1–3) encompass the entire length of the cell whereas DK 4 commences near midline of the cell and extends to posterior end. DM 1 and DM 2 start at the anterior end of the cell and terminate at 1/3 rd of the cell length. Length of the dorsal bris- tles varies from 0.7 to 2.15 µm (average bristle length in DK 1 = 2.15 µm, DK 2 = 1.82 µm, DK 3 = 1.04 µm, DK 4 =1.65 µm, DM 1 = 1.74 µm and DM 2 = 0.7 µm; n = 10 cells). Seven caudal cirri (CC) are arranged in 2 + 2 + 3 pattern at the end of DK 1, 2 & 4 respectively; caudal cirri are about 6.25 µm long ( Figs 1D, I, M , 2B ; Table 1).

Figures

Fig. 1. Photomicrographs of live (A, B, E, F, G, H, J, K), protargol impregnated (C, D, I, L, M) and Feulgen stained (N) cells of Aponotohymena isoaustralis n. sp. A, B – cells in ventral view; C – ventral view of a vegetative cell with 5 transverse cirri arranged in a pseudo row (arrow); D – dorsal view of a vegetative cell; E – ventral view to show the arrangement of cortical granules (arrowheads) and colou- ration; F, G and H – ventral view of different cells showing flexible body; I – anterior portion of the dorsal surface showing dorsal rows (arrowhead); J – anterior portion of the cell showing contractile vacuole (arrowhead); K – cyst; L – anterior hook (arrowhead) of paroral membrane; M – dorsal view showing caudal cirri (2 + 2 + 3) (arrowheads); N – two macronuclei. AZM – adoral zone of membranelles, LMC – left marginal cirri, RMC – right marginal cirri. Scale bars: 20 µm.

Fig. 2. Line diagrams showing protargol impregnated vegetative cells of Aponotohymena isoaustralis n. sp. A – ventral surface; B – dorsal surface.AZM – adoral zone of membranelles, CC – caudal cirri, DK1–4 – dorsal kineties, DM1, 2 – dorsomarginals, EM – endoral membrane, LMC – left marginal cirri, PM – paroral membrane, RMC – right marginal cirri, II/2 – buccal cirri, I/1, II/3, III/3 – frontal cirri, VI/4, VI/3, IV/3, III/2 – frontoventral cirri, – IV/2, V/4, V/3 – postoral ventral cirri, V/2 and VI/2 – pretransverse ventral cirri, II/1, III/1, IV/1, V/1, VI/1 – transverse cirri. Scale bar: 20 µm.