Porifera, or sponges, are multicellular organisms with many pores that filter water. Most sponges live in marine environments, however, some live in brackish environments and about 150 species live in freshwater. Sponges were the first creatures to branch off of the evolutionary tree, which means they are the sister to all other living creatures. Lacking circulatory, digestive, and nervous systems, sponges rely on filtering water unidirectionally to remove wastes from their bodies. Sponges are also immobile species with shapes adapted for the best filtration of water, which rely primarily on filter feeding, however, some species host photosynthesizing microorganisms that provide them with food and oxygen.