are a conspicuous element of the shallow water of waters. They attract the attention of visitors to and, increasingly, are becoming subjects of scientific inquiry. Commonly referred to as sea cucumbers, bêche-de-mer, trepang, or sea slugs, are grouped as one class (Cl. ) in the . They share with other ( , brittle stars, sea urchins, and or sea lilies) a pentaradial body plan and a water vascular system. are restricted to the sea (and with few exceptions are unable to tolerate water), but are common at all latitudes and all depths of the ocean.