Sponges are multicellular organisms. They don't have distinct circulatory, respiratory, digestive and excretory system. Instead, they have a water flow system that support all of these functions. They filter the food from the water that pass through their cells. This is the process of phagocytosis.  *Note that this schema represent a sponges that seems to not exist anymore. It has evolved* ## More : - https://en.wikipedia.org/wiki/Sponge <iframe src="https://en.wikipedia.org/wiki/Sponge" width="100%" height="800"></iframe>