A Stove-pipe Sponge.
Porifera is a phylum from the Animalia kingdom.
Sponges are the simplest animals. They are classified as animals because they are multicellular, heterotrophic, and lack cell walls. They lack true tissues and organs, and have internal skeletons of spongin and/ or spicules of calcium carbonate or silica. Sponges have no body symmetry. The shapes of the bodies of sponges are adapted for maximal efficiency of water flow. Water enters through the central cavity, deposits nutrients, and leaves through a hole called the osculum. All sponges are sessile aquatic animals. Although there are freshwater species, the great majority are marine (salt water) species, ranging from tidal zones to depths exceeding 8,800 m (5.5 mi).