Class Holothuroidea
Body cucumber-such as; no arms; no spines; no pedicellariae; ossicles minute and embedded in muscular wall; anus present; tube feet along with suckers; ambulacral grooves closed; modified tube feet in the type of circumoral tentacles present; madreporite internal. Holothuroidea are commonly termed as sea cucumbers because of their resemblance to cucumber. They differ from the rest of the echinoderms in several respects. Holothurians have greatly elongated oral-aboral axis. The ossicles are highly reduced and are embedded in a muscular, thick and leathery body wall like a result of which the animals are soft-bodied. They either burrow or crawl on the sea-bottom or are found below rocks. As they generally lie on one side, the locomotory tube feet may be present just only on that side of the body limited to the three ambulacra. This side is termed as the sole. In some species though the tube feet may be distributed in five ambulacral areas or all over the body. There are among ten to thirty retractile oral tentacles which are modified tube feet. Sea cucumbers are sluggish animals. Suspended food particles are entangled in the mucus secreted by the oral tentacles. The tentacles are after that stuffed on by one through the mouth into the pharynx and the food particles are sucked off.