The order Porifera is divided into 3 classes.
1. Calcarea: They are small in size and pale in color. Spongin is less. Their skeleton is made of calcium carbonate. They are quite fragile in nature. For example – Sycon gelatinosum.
2. Hexactinellida: These are cup or vase shaped sponges. Large in size. Their spicules are made of silica. Exopinacoderm absent. For example – Euplectella aspergillus.
3 Demosponges: They look like cups or vases and are large. Their choanocytes are narrow. Spicules are made of silica. For example – Spongilla locustris.