(Haeckel, 1860)
Spicules sharpened at both ends, quadrangular in cross section at center, gradually thickening towards periphery. All 10 spicules usually of equal length, sometimes 1 longer. Ectoplasm coarsely vacuolated. Nuclei small, numerous (up to 120). Eight-twelve claviform myonemes next to each spicule. Ectoplasmic cortex of calymma two-layered. Cell body diameter: 0.1 mm; spicule length: 0.16 mm.