|Sea anemones are individual, sessile polyps with cylindrical-shaped bodies. At one end is the oral disk and mouth surrounded by many tentacles, which usually contain stinging cells. The other end is the base used to attach to hard substances. They come in all shapes, colors and sizes. Many are brilliantly colored. Most are small, less than 3.8 cm (1.5 in) in diameter. However, the largest anemone can reach up to 2 m (6.5 ft). When disturbed or threatened, anemones can withdraw their tentacles inside their bodies and basically close themselves in. They are known to form symbiotic relationships with many organisms, including clownfishes, shrimps and crabs. These organisms live within the tentacles of the anemones (without getting stung) or the anemone attaches to the organisms (as with crabs). Either way the anemone's tentacles provide for protection. In return, the anemones eat small particles left over from the organism's feeding.