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Alvinellidae
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<p>The Alvinellidae are a family of small, deep-sea <a href="/facts/Polychaete/Uo2YIINM">polychaete</a> <a href="/facts/Worm/FMrnWM8s">worms</a> endemic to <a href="/facts/Hydrothermal_vent/0xPqNUkY">hydrothermal vents</a> in the <a href="/facts/Pacific_Ocean/bdxgXRVM">Pacific Ocean</a>. Belonging to the order <a href="/facts/Terebellida/BsNhsyqh">Terebellida</a>, the family contains two genera, <i><a href="/facts/Alvinella/7YTcoYe3">Alvinella</a></i> and <i>Paralvinella</i>; the former genus contains two valid species and the latter eight. Members of the family are termed alvinellids. </p><p>The family was first described in 1979 after discoveries made off the <a href="/facts/Gal%25C3%25A1pagos_Islands/pQ7g2hdN">Galápagos Islands</a> by the crew of the <a href="/facts/Deep_Submergence_Vehicle/X9R7FYMd">DSV</a> <i><a href="/facts/DSV_Alvin/IlrCb76E">Alvin</a></i>. The ship subsequently lent its name to the family and genera within it. </p><p>The worms build mucus tubes and extend red feathery gills. Members of the Alvinellidae are noted for their exceptional heat tolerance: one species, <i><a href="/facts/Alvinella_pompejana/7o7sHFuA">Alvinella pompejana</a></i>, is thought to be the most heat-tolerant complex organism on Earth. <a href="/facts/Mitochondria/ErHqrdJ1">Mitochondria</a> start to break down at temperatures of 122–131 °F (50–55 °C), apparently providing an upper limit for <a href="/facts/Eukaryote/SkwyPLMA">eukaryotes</a>. Under laboratory conditions, in a pressurized aquarium with a heat gradient, worms of the species <i>Paralvinella sulfincola</i>, chose water heated to 122 °F (50 °C) and made brief forays into water as hot as 131 °F (55 °C). Unlike other (<a href="/facts/Chemosynthesis/AFUdIqc5">chemosynthetic</a>) vent-dwelling worms, alvinellid worms possess a digestive tract. However, they do rely on an <a href="/facts/Symbiosis/MrBArRGa">episymbiotic</a> relationship with <a href="/facts/Thermophile/HGuP161d">thermophilic</a> <a href="/facts/Bacteria/wC8xSCsU">bacteria</a>; hair-like growths of the bacteria living on the worm's back are thought to offer thermal protection to the worm. </p>