Although it might look like a plant, a sea sponge is an animal that attaches itself to rocks, reefs, and the ocean floor. They are one of the simplest animals in the ocean with no tissue or organs but thousands of pores which let water flow through it continually. Sponges survive by filtering water through themselves and eating the bacteria and tiny organisms found there for food.
Sponges come in many different shapes and colors. They have been around for hundreds of millions of years. Scientists believe they have helped bringing oxygen to the oceans and thus enabled more complex life to evolve on earth.