Tubeworms
They have no skeletal system. They do, however, have a highly vascularized, red "plume" at the tip of their free end. This plume is an organ for exchanging compounds with the environment. The tube worm does not have many predators because Very few creatures live on the sea bottom at such depths. If threatened, the plume may be retracted into the worm's protective tube. The plume provides essential nutrients to bacteria living inside a specialized organ within its body as part of a symbiotic relationship. They are remarkable in that they have no digestive tract, but the bacteria (which may make up half of a worm's body weight turn oxygen, hydrogen sulfide, carbon dioxide, into organic molecules on what their host worms feed.