Phylum Porifera

Porifera (Latin poros, pore; ferre, to bear) are the sponges, the most primitive multicellular animals in the animal kingdom. They are almost entirely aquatic and mostly marine, though a few species live in fresh water, and their body is either radially symmetrical or asymmetrical, sessile, and built at the cellular level of organisation — the cells remain loosely arranged rather than forming true tissues.

Their defining feature is a water transport (canal) system: water enters through tiny pores called ostia that perforate the body wall, flows into a central cavity called the spongocoel, and exits through a larger opening called the osculum. This single flow of water drives food gathering, respiration, circulation and waste removal all at once. The flow is driven by choanocytes (collar cells) — specialised flagellated cells that line the spongocoel and canals. The body is held up by an internal skeleton of calcareous or siliceous spicules, spongin fibres, or both, which give the sponge its shape and rigidity. …