The giant tube worm ("Riftia pachyptila") is an annelid. They live on the floor of the oceans (mainly Pacific Ocean), usually near black smokers, a type of hydrothermal vent. They can tolerate extremely high temperatures and levels of sulfur. They live in symbiosis with certain bacteria. The bacteria enter the mouth of a young tube worm, but when the worm gets older its mouth and gut seal up, trapping the bacteria forever. These bacteria are fed with sulfur compounds and oxygen. The bacteria then turn these compounds into organic molecules on which the host worms feed. 