The porifera phylum consists of sponges. They have a very simple digestive system. They contain a cavity lined with specialized cells that absorb the food that enters or is swept in by cilia. It is not complex at all. They rely on maintaining a constant flow of water through their bodies in order to obtain food, oxygen, and remove wastes.
Purse Sponge
It is a bag usually attached to seaweed or rock. They are flattened with a single osculum at their apex. This apex has a hole which passes water and wastes out. Fresh seawater is absorbed through the surface of the sponge. Plankton and detritus is also absorbed through the surface.
Barrel Sponge
It absorbs water through its pores. In this process, food is also taken in. They must maintain a constant flow of water so that they are never "hungry". Through their pores, they are able to take in oxygen and remove wastes.
Venus Flower Basket Sponge
They contain a cavity lined with specialized cells that allow it to absorb in food, water, and oxygen. They can also sweep in food through their cilia. Their pores also allow them to get rid of wastes. This digestive system is very simple, not complex at all.