Alvinella pompejana, 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 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 work led to important progress in the scientific knowledge of these special worms.
They can reach up to 13 cm (5.1 in) in length and are pale gray, with red tentacle-like gills on their heads. Perhaps most fascinating, their tail ends are often resting in temperatures as high as 176 °F (80 °C), while their feather-like heads stick 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 research suggests 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 sustained temperatures of from 45 to 60 °C (113 to 140 °F) and even 105 °C (221 °F) for a short time, 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 cm (5.1 in), Pompeii worms have "hairy" backs; these "hairs" are actually colonies of bacteria such as Nautilia profundicola, which are thought to afford the worm some degree of insulation. Glands on the worm's back secrete a mucus on which the bacteria feed, a form of 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 matches 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 1 cm thick. The bacteria may possess special proteins, "eurythermal enzymes", providing the bacteria—and by extension the worms—protection from a wide range of temperatures. The bacteria may 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. Since their internal temperature has yet to be measured, a Pompeii worm may survive 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. Its posterior end is exposed to extreme temperatures; the anterior end stays at a much more comfortable 22 °C (72 °F).
The original description was made by Desbruyères & Laubier (1980, pages 268-273) as the first known member of the alvinellids. In 1986, they refined their description (page 2229) and identified another species, Alvinella caudata.