Giant tube worms (Riftia pachyptila) anchored on the seabed by a hydrothermal vent. These marine invertebrates are a key part of the ecosystem of deep ocean hydrothermal vents. They can tolerate high temperatures, 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 that are used by the tube worms. The white tube of a tube worm is made of chitin. The red structures, called plumes, contain haemoglobin that combines with the hydrogen sulphide and transfers it to the bacteria. Photographed on the East Pacific Rise.