The sponges or poriferans (from Latin porus "pore" and ferre "to bear") are animals of the phylum Porifera. Porifera translates to "Pore-bearer". They are primitive, sessile, mostly marine, water dwelling filter feeders that pump water through their bodies to filter out particles of food matter. Sponges represent the simplest of animals. With no true tissues (parazoa), they lack muscles, nerves, and internal organs. Their similarity to colonial choanoflagellates shows the probable evolutionary jump from unicellular to multicellular organisms. However, recent genomic studies suggest they are not the most ancient lineage of animals, but may instead be secondarily simplified.

There are over 5,000 modern species of sponges known, and they can be found attached to surfaces anywhere from the intertidal zone to as deep as 8,500 m (29,000 feet) or further. Though the fossil record of sponges dates back to the Neoproterozoic Era, new species are still commonly discovered.