(Haeckel, 1887)
Spicules prismatic, smoothly 4-edged in cross section, very long and thin, linked in cell center by edges of small 5- or 6-edged pyramidal bases. Cell body spherical, colorless, with abundant zooxanthellae. Ectoplasmic cortex single-layered. Spicules with 16 myonemes. Diameter of cell body: 0.07 mm; spicule length: 0.3 mm.