Riftia pachyptila, commonly known as the giant tube worm and less commonly known as the giant beardworm, is a marine invertebrate in the phylum Annelida related to tube worms commonly found in the intertidal and pelagic zones. R. pachyptila lives on the floor of the Pacific Ocean near hydrothermal vents. R. pachyptila was discovered in 1977 on an expedition of the American bathyscaphe DSV Alvin to the Galápagos Rift led by geologist Jack Corliss. The discovery was unexpected, as the team was studying hydrothermal vents and no biologists were included in the expedition. Many of the species found living near hydrothermal vents during this expedition had never been seen before. R. pachyptila develops from a free-swimming, pelagic, nonsymbiotic trochophore larva, which enters juvenile (metatrochophore) development, becoming sessile, and subsequently acquiring symbiotic bacteria. The symbiotic bacteria, on which adult worms depend for sustenance, are not present in the gametes, but are acquired from the environment through the skin in a process akin to an infection. The digestive tract transiently connects from a mouth at the tip of the ventral medial process to a foregut, midgut, hindgut, and anus and was previously thought to have been the method by which the bacteria are introduced into adults. After symbionts are established in the midgut, they undergo substantial remodelling and enlargement to become the trophosome, while the remainder of the digestive tract has not been detected in adult specimens.