These tubular echinoderms can be found in oceans all over the world – in some deep sea environments they can be found in very large numbers roving along the ocean floor in search of food. The diet of most sea cucumber consists of decaying organic matter and plankton. Though they don’t resemble other echinoderms at first glance, they are technically radially symmetrical along their horizontal axis and crawl about on their side. One of their most remarkable adaptations is their “catch” collagen that forms their body wall – it can be loosed or tightened at will, allowing them to essentially liquefy their bodies to squeeze through tight spaces.

https://en.wikipedia.org/wiki/Sea_cucumber