Riftia pachyptila(Vestimentifera) is a giant tubeworm living around the volcanic deep-sea vents of the East Pacific Rise. This animal is devoid of a digestive tract and lives in an intimate symbiosis with a sulfur-oxidizing chemoauto-trophic bacterium. This bacterial endosymbiont is localized in the cells of a richly vascularized organ of the worm: the trophosome. These organisms are adapted to their extreme environment and take advantage of the particular compo-sition of the mixed volcanic and sea waters to extract and assimilate inorganicmetabolites, especiallycarbon, nitrogen, oxygen and sulfur. .
