Sea cucumbers are sausage-shaped echinoderms that include about 1250 species. Sea cucumbers have a reduced endoskeleton that consists of tiny ossicles (made of calcium carbonate) embedded in the body wall. Sea cucumbers have a mouth at the front of their body that is surrounded by tentalces (the number and structure of the tentacles varies among the different subgroups of sea cucumbers).
Sea cucumbers have a worldwide range. Most live on the sea floor, but some species burrow into the substrate or hide in crevices or under rocks. A small number of species are free-swimming. Sea cucumbers sometimes eject their entire digestive tract either through their mouth or anus (depending on species) and this behavior is thought to be a form of defense or to distract predators. The lost organs are usually regenerated.
Sea cucumbers generally measure between 4 and 12 inches, although some species are much smaller or larger than this range. They are usually scavengers, feeding on plankton and decaying organic matter that falls to the sea floor.