Belonocystis tubistella Rainer, 1968

Nicholls, Kenneth H., 2012, Structure of Organic Spines in the Rhizarian Protist Belonocystis tubistella Rainer, 1968, and a Description of Belonocystis quadrangularis n. sp. (Cercozoa, Insertae Sedis), Acta Protozoologica 51 (1), pp. 21-28 : 22

Belonocystis tubistella Rainer, 1968 ; Figs 1a–d , 2a–h

Cells were spherical, 8–16 µm in diameter and moved slowly among the detritus of the microscopic preparation, facilitated by their fine filopodia ( Fig. 1a ) which were difficult to see, even with high magnification phase-contrast microscopy. Cells contained an eccentrically located nucleus of about 4 µm in diameter with a prominent nucleolus ( Fig. 1a, b, d ). From one to four functional contractile vacuoles were present, ranging in size up to about 4 µm in diameter, with size apparently dependent upon the stage of the diastolesystole cycle.

The most distinctive feature of these cells was the radiating series of spines with their broad tent-shaped bases ( Fig. 1 ). Spines were 10–15 µm long, consisting of a hollow shaft that was widest (0.1–0.3 µm diameter) near the base and tapered to a very fine distal point ( Fig. 2a–c ). The bases of the shafts were divided into four curved arms that formed a basal tent-like structure covered by a membranous sheet that was perforated with circular to elliptical pores in close proximity forming a mesh-work appearance to the spine bases ( Fig. 2e, g, h ). In the living, uncollapsed state, the top portion of the spine base appeared funnel-shaped with sloping sides that abruptly straightened to nearly parallel sides where scale bases abutted one another ( Figs 1a, b , 2d ). Scale bases were 2–3 µm wide and pores in the sheet mesh-work structure forming the bases were 0.1–0.3 µm in diameter.

Figures

Fig. 1. Belonocystis tubistella. a – diagrammatic representation of a living cell; b–d – images of living cells. N – nucleus, n – nucleolus, fv – food vacuole, cv – contractile vacuole, f – filose pseudopod, ss – spine.

Fig. 2. Belonocystis tubistella scale structure. a–c – whole cells, died, TEM images showing the investiture of radiating spines; d–f – diagrammatic depiction of the arrangement (d) and structure of spine bases showing meshed structure of an intact scale base (e) and the collapsed state of a dried spine base (f). The meshed structure is not included in f, to visualize better the collapsed shape of the spine; g–h – TEM images showing the meshed structure of the spine bases. The arrows in h are examples of the distorted (high “shoulder” effect) shape of collapsed spine bases (as illustrated with the arrow in f).