What are real sponges?

Sponges are sea animals of the phylum Porifera (meaning "pore bearer") . They are multi-cellular organisms that have bodies full of pores and channels allowing water to circulate through them. They consist of jelly-like mesohyl sandwiched between two thin layers of cells. Sponges also have unspecialized cells that can transform into other types of cells. Sponges do not have nervous, digestive or circulatory systems. Instead, most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes.

Sponges are worldwide in their distribution, living in a wide range of ocean habitats, from the polar regions to the tropics. Most live in quiet, clear waters, because sediment stirred up by waves or currents would block their pores, making it difficult for them to feed and breathe. The greatest numbers of sponges are usually found on firm surfaces such as rocks, but some sponges can attach themselves to soft sediment by means of a root-like base.