Giant tube worms (Riftia sp.). These marine invertebrates live near hydrothermal vents in the Pacific Ocean and obtain nutrients from the water by symbiosis with bacteria living in their bodies. The bacteria turn inorganic chemicals produced by the vent, such as hydrogen sulphide and carbon dioxide, into organic molecules. The white part of a tube worm is made of chitin. The red structures (plumes) contain haemoglobin that combines with hydrogen sulphide and transfers it to the bacteria.