Class 1. Calcarea (L., calx=lime) or Calcispongiae (L., calcis= lime+ spongia= sponge)

• Small-sized calcareous sponges, below 10 cm in height.
• Solitary or conical; body shape vase-like or cylindrical.
• They may show asconoid, Syconoid, or leuconoid structures.
• A skeleton of separate one or three or four-rayed calcareous spicules.
• Exclusively marine.

Order 1. Homocoela (=Asconosa)

• Asconoid sponges with cylindrical and radially symmetrical bodies.
• Body wall thin, not folded. Choanocytes line the Spongocoel.
• Often conical.
• Examples: Leucosolenia, Clathrina.

Order 2. Heterocoela (=Syconosa)

• Syconoid and leuconoid sponges having a vase-like body.
• The body wall is thick, folded. Choanocytes line the flagellated chambers (radial canals) only.
• Spongocoel is a line by flattened endoderm cells.
• Solitary or conical
• Examples: Sycon or Scypha, Grantia.