Sea cucumber

Sea cucumbers are echinoderms from the class Holothuroidea (ˌhɒləˌθjʊəˈrɔɪdi.ə,_ˌhoʊ-). They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are found on the sea floor worldwide. The number of known holothurian (ˌhɒləˈθjʊəri.ən,_ˌhoʊ-) species worldwide is about 1,717, with the greatest number being in the Asia-Pacific region. Many of these are gathered for human consumption and some species are cultivated in aquaculture systems. The harvested product is variously referred to as trepang, namako, bêche-de-mer, or balate. Sea cucumbers serve a useful role in the marine ecosystem as they help recycle nutrients, breaking down detritus and other organic matter, after which bacteria can continue the decomposition process. Like all echinoderms, sea cucumbers have an endoskeleton just below the skin, calcified structures that are usually reduced to isolated microscopic ossicles (or sclerietes) joined by connective tissue. In some species these can sometimes be enlarged to flattened plates, forming an armour. In pelagic species such as Pelagothuria natatrix (order Elasipodida, family Pelagothuriidae), the skeleton is absent and there is no calcareous ring. Sea cucumbers are named for their resemblance to the fruit of the cucumber plant. Most sea cucumbers, as their name suggests, have a soft and cylindrical body, more or less lengthened, rounded off and occasionally fat in the extremities, and generally without solid appendages. Their shape ranges from almost spherical for "sea apples" (genus Pseudocolochirus) to serpent-like for Apodida or the classic sausage-shape, while others resemble caterpillars. The mouth is surrounded by tentacles, which can be pulled back inside the animal. Holothurians measure generally between 10 and 30 centimetres long, with extremes of some millimetres for Rhabdomolgus ruber and up to more than 3 metres for Synapta maculata. The largest American species, Holothuria floridana, which abounds just below low-water mark on the Florida reefs, has a volume of well over , and long.