Any of 1,100 species of echinoderms constituting the class Holothurioidea, found in all oceans, mostly in shallow water. The soft, cylindrical body is 0.75 in. (2 cm) to 6.5 ft (2 m) long and 0.4–8 in. (1–20 cm) thick. It is usually dull, dark, and often warty. The internal skeleton consists merely of numerous tiny bits in the skin. Most species have five rows of tube feet extending from mouth to anus. The 10 or more retractile tentacles surrounding the mouth are used for taking food (mud containing nutrients or small aquatic animals) or burrowing. Locomotion is sluglike. See alsoshellfish.