Haeckel, 1862, emend. Schewiakoff, 1926
Spicules long, straight, of equal length, simply crossed in cell center, generally cylindrical, smooth. Endoplasm in two concentric zones. Ectoplasm vacuolar. Myonemes very thin. Gametogenesis in oblong or spherical cysts.
One genus: Acanthochiasma
Six species:
Acanthochiasma fusiforme
Acanthochiasma hertwigi
Acanthochiasma planum
Acanthochiasma quadrangulum
Acanthochiasma rubescens
Acanthochiasma serrulatum