(a) Sponges

Habitat: All sponges are aquatic, mostly marine, rarely fresh water (e.g., Spongilla), solitary or colonial, sessile (attached to the substratum). Sponges like warmer water, they are not usually found in cold water.

Body Form: Their body is porous, viz., provided with pores. The pores are of two types: inhalant pores are called ostia (sing, ostium) and exhalent pores are known as oscula.

Symmetry: Most of the sponges are asymmetrical. Some are radially symmetrical.

Germ Layers:  The sponges are the first multicellular diploblastic animals, i.e. derived only from two embryonic germ layers, viz., ectoderm and endoderm.

Level of Organization: The sponges have cellular level of organization.

Canal System: This system consists of pores and canals.