Sponges are filter feeders.
Sponges come in many colors.
They sift plankton (very small plants and animals that drift in the ocean) out of the water. They do this by means of a wriggling whip that in moving in a snake-like fashion creates a current. The current causes water to flow in and out of a chamber. The chamber is lined with mucus so dissolved organic matter, diatoms and other plankton get in it. The out-flowing water is channeled together and flows out of the larger holes you see on a sponge. The intake holes are too small to see with the naked eye.
We sprinkle sand over the exhaust hole and watch it blow away to demonstrate this flow of water.