An echinoderm in the class Holothuroidea. Sea cucumbers possess a flexible, elongated body and leathery skin, and tentacles surrounding the mouth. Although they don't superficially resemble other members of the phylum Echinodermata, they retain pentameral (five-rayed) symmetry, with five rows of tube feet running from the mouth down along the sides of the body. Sea cucumbers are an abundant and diverse group that are found in nearly every marine environment, but are most diverse on tropical, shallow-water coral reefs.They are economically important in two main ways. They produce chemical compounds that are of interest to pharmaceutical firms, and as a food item in Asia, they form the basis of a multimillion-dollar industry that processes the body wall for sale as beche-de-mer or trepang.