Three concentric shells. Outermost with regular, circular pores with well developed polygonal frames, usually bearing short bristle-shaped spines on the nodes (broken off in the specimen photographed); no primary (conspicuously larger) radial spines (see remark for Thecosphaera inermis). Outermost shell diameter: 70-100 µm.
Ref.: Hollande and Enjumet (1960), Boltovskoy and Riedel (1980).