Alvinella Paralvinella The Alvinellidae are a family of small, deep-sea polychaete worms endemic to hydrothermal vents in the Pacific Ocean.

Belonging to the order Terebellida, the family contains two genera, Alvinella and Paralvinella; the former genus contains two valid species and the latter eight.

The family was first described in 1979 after discoveries made off the Galápagos Islands by the crew of the DSV Alvin.

Members of the Alvinellidae are noted for their exceptional heat tolerance: one species, the Pompeii worm (Alvinella pompejana), is thought to be the most heat-tolerant complex organism on Earth.

Mitochondria start to break down at temperatures of 122–131 °F (50–55 °C), apparently providing an upper limit for eukaryotes.