(Haeckel, 1860)
Two main spicules longer and morphologically different from other 8. They may be equal, or (more rarely) differ in width, with blunt ends, or with lanceolate, sharp distal ends. Sometimes with longitudinal keel. Secondary spicules thinner and shorter than main. Length of main spicules: 0.16-0.18 mm, secondary spicules: 0.11 mm.