What anatomy of a sponge causes the water flow though it?

The anatomy of sponge which causes water to flow through it is the poriferan  ventilation general anatomy.

Sponges do not have nerves or muscles and they do not move their only way which is relying on water flow in order to remove movement of sperm, remove gas exchange, remove wastes, and bringing food.

Because of architecture of sponge and action of choanocytes then the flow of water is being utilized efficiently by the sponge.

Water flows to spongocoel and to sponge through small openings which are found in the sponge, and out of sponge through Osculum which are the large openings.

It has thousands of pores called OSTIA which let water flow through it continually.

Sponges (poriferans) are very simple animals that live permanently attached to a location in the water. Most sponges live in salt water - only about 150 species live in fresh water. Sponges have tiny pores in their outer walls through which water is drawn. Cells in the sponge walls filter food from the water.