Sponges

Sponges, the phylum Porifera, are the simplest multicellular animals with no true tissues, organs, or nervous system, yet they filter enormous volumes of water for food and oxygen through pores across their bodies. Specialized cells called choanocytes generate water flow through an internal canal system and capture bacteria and organic particles as food. A sponge's skeleton is built from mineral spicules, protein fibers, or both, giving different species their characteristic glassy, rigid, or springy texture. Sponges are entirely aquatic, mostly marine, and are found from shallow reefs to some of the deepest parts of the ocean floor.