Sponges are the simplest of the multicellular animals. Water is drawn into the sponge through pores (incurrent openings) and pumped through the interior by the beating of whip-like extensions on the cells called flagella. As water passes through the sponge, food and oxygen are filtered out. The water exits into the body's interior cavity and out the animals one or more large excurrent openings. Sponges come in many sizes, colors and shapes.