(Dreyer)
Fully grown specimens with 4 concentric, latticed shells. Outermost thin-walled, with very small pores. Third shell thicker, with large, irregularly shaped pores. Surface covered with many short, stout, 3-bladed spines, at one of the poles spines may be denser and larger, forming a pylome. Major diameter of outermost shell: 100-160 µm.
Ref.: Petrushevskaya (1967).
electron- and light microsc.
stages of growth in skeletons