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Alvinella pompejana, (also known as the Pompeii worm), is a species of deep-sea polychaete worm (commonly referred to as "bristle worms"). It is an extremophile found only at hydrothermal vents in the Pacific Ocean, discovered in the early 1980s off the Galápagos Islands by French marine biologists.
In 1980 the French researchers Daniel Desbruyères and Lucien Laubier, just few years after the discovery of the first hydrothermal vent system, identified one of the most heat-tolerant animals on Earth — Alvinella pompejana, the Pompeii worm. It was described as a deep-sea polychaete that resides in tubes near hydrothermal vents, along the seafloor. In 1997 marine biologist Craig Cary and colleagues found the same worms in a new section of Pacific Ocean, near Costa Rica, also attached to hydrothermal vents. The new discovery and subsequent researches led to important progress in the scientific knowledge of these very special worms.
They can reach up to 5 inches in length and are pale gray with red tentacle-like gills on their heads. Perhaps most fascinating, is that their tail end is often resting in temperatures as high as 176 °F (80 °C), while their feather-like head sticks out of the tubes into water that is a much cooler 72 °F (22 °C). Scientists are attempting to understand how Pompeii worms can withstand such extreme temperatures by studying the bacteria that form a "fleece-like" covering on their backs. Living in a symbiotic relationship, the worms secrete mucus from tiny glands on their backs to feed the bacteria, and in return they are protected by some degree of insulation. The bacteria have also been discovered to be chemolithotrophic, contributing to the ecology of the vent community. Recent researches suggest that the bacteria might play an important role in the feeding of the worms.
Attaching themselves to black smokers, the worms have been found to thrive at temperatures of up to 80 °C (176 °F), making the Pompeii worm the most heat-tolerant complex animal known to science after the tardigrades (or water bears), which are able to survive temperatures over 150 °C.
Reaching a length of up to 13 centimeters (5 inches), Pompeii worms are a pale grey with "hairy" backs; these "hairs" are actually colonies of bacteria which are thought to afford the worm some degree of insulation. Glands on the worm's back secrete a mucus which the bacteria feed on (see symbiosis). The Pompeii worms form large aggregate colonies enclosed in delicate, paper-thin tubes.
Pompeii worms get their name from the Roman city of Pompeii that was destroyed during an eruption of Mount Vesuvius in AD 79. Its family name Alvinellidae and genus name Alvinella both derive from DSV Alvin, the three-person submersible vehicle used during the discovery of hydrothermal vents and their fauna during the late 1970s. The family Alvinellidae contains eight other species, but none match the Pompeii worm's heat tolerance.
While it is not yet known precisely how the Pompeii worm survives these severe vent conditions, scientists suspect the answer lies in the fleece-like bacteria on the worm's back; this layer may be up to a centimetre thick. The bacteria may possess special proteins, "eurythermal enzymes", providing the bacteria—and by extension the worms—protection from a wide range of temperatures. It is plausible that the bacteria also provide thermal insulation. Studies are hampered by the difficulties of sampling; to date, Pompeii worms have not survived decompression.
Pompeii worms simultaneously keep their heads (including the gills) in much cooler water while their tails are exposed to hot water (see below). Since their internal temperature has yet to be measured, it is plausible that a Pompeii worm survives exposure to hot water by dissipating heat through its head to keep its internal temperature within the realm previously known to be compatible with animal survival.
Thought to subsist on vent microbes, the Pompeii worm pokes its head out of its tube home to feed and breathe. It is the posterior end that is exposed to extreme temperatures; the anterior end stays at a much more comfortable 22 °C (72 °F).
- D.Desbruyères, L.Laubier - Alvinella pompejana gen.sp. nov., Ampharetidae aberrant des sources hydrothermales de la ride Est-Pacifique - Oceanologica Acta, 1980
- NSF-OLPA - Scientists Succeed at First-Ever Attempt to Sequence DNA at Sea (2001)
- Grzymski, J. J.; et al. (2008). "Metagenome analysis of an extreme microbial symbiosis reveals eurythermal adaptation and metabolic flexibility". PNAS 105 (45): 17516–17521. doi:10.1073/pnas.0802782105. PMID 18987310.