Sponges are not colored. Sponge body cavities are vast and exposed to the outside environment, allowing the sponge to ingest food (Dawkins 2004). Sponges lack internal organs and a nervous system. However they do have cells that contain sponge collagen which acts as nerves and muscles for moving about (Dawkins 2004). Sponges are invertebrates; they belong to the phylum Porifera. They make up more than 5,000 species of marine organisms found in all oceans except for the Antarctic Sea. Most sponges are soft and porous, but a few hard varieties also exist. All sponges are filter-feeders that use currents, wind, or water movement to filter food from their surroundings. Some sponges can even move around to find better locations to filter water (Dawkins 2004). Sponges were first described by Aristotle in his book "Historia Animalium" where he coined the term "spongia" to describe any substance that absorbs liquids through pores or holes. This term was later used by Theophrastus and Dioscorides Anazarbos to describe sponges that were used for making sponges. In 1753, Carl Linnaeus added the word "sponge" to each species name he classified under the genus Cryptum.