Sea Cucumbers (Holothuroidea)

Sea cucumbers, or holothurians, are echinoderms that are generally long and wormlike, so a casual observer might not realize they are related to starfish and sea lilies. They keep the five-rayed symmetry of echinoderms, with five rows of tube feet running from the mouth along the body. In most species the skeleton is reduced to microscopic spicules, often shaped like wheels, bars or anchors. One way to think of a sea cucumber is as a sea urchin lying on its side, stretched out and missing much of its skeleton. They are common in tidepools and other shallow water, and in parts of the deep sea the ocean floor swarms with vast herds of them.