Animals in the Holothuroidea class are commonly called holothurians. They are marine animals, classified as echinoderms alongside sea urchins, starfish, brittle stars and comatulids. Their elongated and soft circular section body gives has gotten them the nickname of 'sea cucumber'.
The animal is radially symmetric and divided into five areas, like all echinoderms. Adults do not swim, but crawl along the seabed. Holothurians are detritivores that feed by filtering sediment collected through the retractile tentacles that surround their mouths. Some species may bury themselves.
If threatened, a holothurian contracts and hardens its skin. In the event of a blatant attack, some holothurians may eject a filament composed of a sticky liquid and may even expel part of their organs to tangle the enemy in a paralysing trap.
There are many species of holothurians, found across a wide range of latitudes and depths.