(Haeckel, 1860)
Distal half of spicules thin, cylindrical, or slightly compressed, tapering toward simple or bifid apex; proximal half 3-6 times broader, 4-winged in cross section, with 6 longitudinal rows of opposite apophyses. Edges of broader wings giving rise to 3-4 pairs of strong conical teeth. Edges of smaller (sagittal) wings producing 3-4 pairs of short, broad, triangular teeth, which in turn bear slender conical teeth on opposite sides. Spicule bases pyramidal, with small leaf-cross. Eight-twelve myonemes per spicule. Central capsule large, whitish, ectoplasmic cortex 2-layered. Length of spicules: 0.2-0.4 mm, width of proximal section: 0.016 mm, distal: 0.002-0.004 mm.