Thigmokeronopsis stoecki

Chen, Xumiao, Li, Liqiong, Hu, Xiaozhong, Shao, Chen, Al-Farraj, Saleh A. & Al-Rasheid, Khaled A. S., 2013, A Morphogenetic Description of Thigmokeronopsis stoecki Shao et al., 2008 (Ciliophora, Hypotricha) and a Comparison with Members of the Family Pseudokeronopsidae, Acta Protozoologica 52 (2), pp. 65-72 : 68

Morphogenesis of Thigmokeronopsis stoecki ( Figs 8–23 )

Stomatogenesis and cirral streaks. Stomatogenesis commenced with the apokinetal appearance of the oral primordium, an anarchic field of basal bodies beneath the old undulating membranes (UMs) in the proter and a small elliptical field of basal bodies on the cell surface adjacent to the left row of the midventral cirri in the opisthe. Simultaneously, all the old oral apparatus and cirri remained apparently unchanged and were not involved in the formation of primordia ( Figs 8 , 16 ).

In the following stage, by further proliferation of basal bodies, both oral primordia gave rise to the new adoral membranelles in a posteriad direction. The anlagen for the new undulating membranes (UM-anlagen) were also generated to the right. In both dividers, the fronto-ventral-transverse cirral anlagen (FVT-anlagen) appeared on the cell surface as anarchic oblique streaks. At the same time, the old oral apparatus began to loose and be resorbed while the midventral complex remained unchanged, as did other old cirri ( Figs 9 , 17 ).

As shown in Fig. 10 the development of primordia in both dividers was remarkably simultaneous. As the further proliferation of the adoral membranelles proceeded, the UM-anlagen became longer and wider and gave rise to one cirrus anteriad, which would become the leftmost frontal cirrus. The FVT-anlagen organized into dozens of oblique streaks and each streak developed into several new cirri.

Soon after, the anterior ends of the two new adoral zones of membranelles (AZMs) started to arch to the right, although the two new UM-anlagen did not yet split. The FVT-anlagen differentiated clearly and each streak (except some of the last streaks) generated the first two strong cirri (forming the midventral pairs) and others that were fine and arranged closely (forming the thigmotactic cirri) ( Figs 12 , 18, 19 ).

Subsequently, new AZMs developed completely and the UM-anlagen split longitudinally to form the new paroral and endoral membranes. New cirri began migrating towards their final positions ( Figs 13, 15 , 21–23 ). Finally, streak n (the last FVT-anlagen) formed four cirri in each divider, of which the anterior two continued to migrate anteriad to become the frontoterminal cirri, while the posterior two would become the transverse cirri. Similarly, streak n-1 to n-6 gave two midventral and one transverse cirrus, and streak II (the first FVT-anlage) generated one frontal and one buccal cirrus. In addition, streak III to n-7 gave two midventral and several thin thigmotactic cirri. Before the separation of proter and opisthe, these fine cirri combined, migrated toward the left and located themselves between the midventral complex and the left marginal cirral row, that is, the thigmotactic field ( Figs 13–15 , 22, 23 ). The midventral cirri, however, formed two separate pseudorows instead of a typical zig-zag pattern.

Finally, the old oral apparatus and most of the cirri were resorbed and the daughters began to separate.

Marginal and dorsal structures. Shortly after the beginning of morphogenesis, the marginal cirral anlagen originated de novo both in the proter and the opisthe ( Fig. 10 ). These anlagen then stretched and later gradually replaced the parental rows ( Figs 12, 13, 15 , 20 ).

The anlagen of the new dorsal kineties also developed de novo ( Fig. 11 ) through two anlagen close to the parental rows. The anlagen subsequently elongated by basal body proliferation until they were apparent through the whole cell length.

Division of nuclear apparatus. It was evident that the macronuclear nodules fused into numerous (with about 40 segments) masses ( Fig. 11 ). In the middle to late stages, these masses began to elongate, divide into numerous oval macronuclear nodules, and then, distributed into the daughters. Division of the micronuclei was not observed.

Figures

Figs 8–15. Infraciliature of Thigmokeronopsis stoecki during divisional process. 8 – ventral view of an early divider, arrowheads and arrow show the oral primordium of the opisthe and proter respectively; 9 – ventral view, double-arrowheads indicate the parental membranelles disaggregating, arrows indicating the fronto-ventral-transverse cirral anlagen and arrowheads marking the oral primordia for each of the dividers; 10, 11 – ventral and dorsal views of the same divider at mid-stage, in Fig. 10 arrows indicate the left marginal row anlagen and arrowheads mark the undulating membranes anlagen for each divider, in Fig. 11 arrows indicate the dorsal kineties anlagen and arrowheads mark the right marginal row anlagen; 12 – ventral view, arrowhead indicates right marginal row anlage in the opisthe, and arrows mark the first frontal cirri generated from the undulating membrane anlagen; 13, 14 – ventral views of a late divider, arrows indicate the new left marginal rows, arrowheads mark the new buccal cirri, double-arrowheads show the frontoterminal cirri (Fig. 14 to show the details); 15 – ventral view of a late stage divider about to separate, to show the formation of new frontoterminal cirri (arrows), the thigmotactic cirri (arrowheads) and the transverse cirri (double-arrowheads). Scale bars: 50 µm.

Figs 16–23. Photomicrographs of Thigmokeronopsis stoecki during morphogenesis after protargol impregnation. 16 – ventral view, arrows indicate the anarchic field of basal bodies; 17 – ventral view of proter, arrow marks disorganized parental undulating membranes, and arrowheads indicate the fronto-ventral-transverse cirral anlagen; 18 – ventral view of a mid-staged divider, noting the development of adoral zone of membranelles; 19 – ventral view of proter, to show the newly formed first frontal cirrus (arrow), the buccal cirrus (double-arrowheads), and thigmotactic cirri (arrowheads); 20, 21 – ventral views, to show the newly formed right marginal rows (arrows in Fig. 20); 22, 23 – ventral views of the same divider, to show the new buccal cirrus (arrow in Fig. 22), frontoterminal cirri (arrow in Fig. 23), transverse cirri (arrowhead in Fig. 23) and the thigmotactic cirri (double-arrowheads in Fig. 23). Scale bars: 40 µm.