Valonia ventricosa are single-celled algae that range between one and few centimetres. In rare cases, they can reach sizes exceeding 5cm. They range from grass-green to dark green, and some are even a blackish colour.
Weirdly, a lot of the literature covering these organisms seems to be pre-1950. This X-ray crystallography project in 1937 identified key structures in the cell wall of V. ventricosa:
It is found to consist of layers in which the cellulose chains in any one layer are inclined to those in the preceding and subsequent layers at an angle which is on the average rather less than a right angle.
The two sets of striations on the layers of the wall correspond closely to the meridian and spiral directions of cellulose chains, while the extinction directions, being defined both by the directions and by the relative proportions of the two sets of cellulose chains, lie in variable positions between. The development of the rhizoids has been investigated and found to be associated with regions of the wall adjacent to the poles of the spiral.
Although the authors hesitate to speculate on their function, has any progress in the field suggested the fibres identified in this 1948 Nature paper be involved in sustaining such a massive cell (Figure below)?
So it seems like the cell wall structure has been categorised long ago. But what allows these single-celled organisms to get so big? Is it the plant-like cell wall, or something else? I was under the impression that cells would burst or collapse well before reaching this size.