Riftia pachyptila is the largest of all Siboglinidae, reaching 1.5 m in length. Virtually all of their nutritional requirements are derived from the bacteria in the body, which can make up 15% of the animal's total body weight. Riftia lives around deep-sea hydrothermal vents from which heated water, sulfide and carbon dioxide are ejected. The palps of project from the tube and are richly supplied with blood vessels that serve for the respiratory purposes of the worm, but also to transport the sulphide and carbon dioxide that are needed by the symbiotic bacteria.