(Haeckel, 1860)
Spicules 4-edged, pyramidal, 2 opposed edges serrated proximally (serrations fine, densely arrayed, proximally directed), each with 6-8 thread-like myonemes. Live specimens orange to gray-yellow in color. Shell diameter: 0.5 mm; cell body: 0.09-0.12 mm; spicule length: 0.2-0.24 mm, width: 0.008 mm.