Animals in the phylum Porifera, such as sponges, do not have a developed digestive system. Instead, they rely on a simple process called filter feeding to obtain and digest food.

The body structure of sponges is designed in such a way that water moves through the central body cavity of the body, where it can filter out food and also absorb the dissolved oxygen, along with eliminating waste materials. This kind of system is called water transport or canal system as water enters through the ostia into the central body cavity and goes out through the osculum.