Haeckel, 1882, emend. Schewiakoff, 1926
Skeleton of 20 radial spicules, of different size and shape, two longer and thicker than other 18. All fused in cell center. Cell body cylindrical or oval, endoplasm with numerous nuclei and zooxanthellae. Capsular wall thin, peripheral. Ectoplasm covered with periplasmic cortex, attached to each spicule by 6-24 myonemes.
Two genera:
Genus Amphibelone
Genus Amphilithium