Sponges are similar to other animals in that they are multicellular, lack cell walls, and produce sperm cells. Unlike other animals, they lack true tissues and organs, and have no body symmetry. The shapes of their bodies are adapted for efficient water flow through their central cavity.
Many sponges have simple, internal skeletons. All sponges lack the ability to move. Although there are freshwater species, the great majority are salt water species, ranging from tidal zones to depths exceeding 8,800 meters.
Most of the known species feed on bacteria and other food particles in the water, but some host micro-organisms in a symbiotic relationship. A few species of sponge have become carnivores that prey mainly on small crustaceans.[