Giant Tube Worm (Riftia pachyptila)

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A vestimentiferan annelid found at eastern Pacific hydrothermal vents, reaching a metre or more, with a white chitinous tube and a red plume rich in haemoglobin. The adult has no mouth and no functional gut: it houses chemoautotrophic sulphur-oxidising bacteria in a specialised organ, the trophosome, and lives entirely on the carbon those symbionts fix. It is the clearest single demonstration that a large animal can be built without any sunlight anywhere in its food chain. First described from the 1977 Galapagos Rift discovery; the symbiosis was established by Cavanaugh and colleagues in 1981.