The heart of a typical adult human can pump about 2,000 gallons of blood per day. But that’s anemic compared to the pumping capacity of a sponge -- the living kind, not the kind you use to wash off your kitchen cabinets. The amount of water it pumps can be up to 20,000 times the volume of its own body. For a good-sized sponge, that can be almost 20,000 gallons a day.
A young sponge anchors itself to the ocean floor, then it stays put. Since it can’t go out and catch food, the food has to come to it. In fact, a sponge eats by filtering food from the water -- living organisms like bacteria, or bits of dead organisms and other waste that floats through the oceans.
The water enters through millions of tiny pores in the sponge’s body. It passes through canals to chambers that contain what are known as collar cells. These consist of two parts. The first is a flagellum -- a tiny filament that whips back and forth, moving water through the sponge. Each one barely tickles the water around it, but there are so many of them that they generate a good flow.
The second part of the cell is the collar itself -- a cup that captures bits of food from the water, providing the nutrients to keep the sponge going. The filtered water moves into a cavity in the middle of the sponge, carrying nitrogen, carbon dioxide, and other wastes. The water then squirts out through an opening at the top of the sponge known as the osculum -- the “little mouth” -- expelled by a busy sponge.