The huge arachnid has been named the Trogloraptor, or “cave robber”, in reference to its chosen home and “extraordinary, raptorial” claws, which suggest that it is a fierce, specialised predator.
Measuring about four centimetres wide when its legs are extended, the spider is extremely important in evolutionarily terms because it represents not only a new genus and species, but also a new family, Trogloraptoridae.
The historic discovery revealed on yesterday/today (Friday August 17th) was made by a team of arachnologists from the California Academy of Sciences working with ‘citizen’ scientists from the Western Cave Conservancy who found the spiders living in caves in southwest Oregon.
Colleagues from San Diego State University found more of the arachnids in old-growth redwood forests.
The regions are part of a swathe of forest stretching from California to British Colombia which are known for rare species.
Deep forests there are also said to be the lair of the legendary Bigfoot - although the researchers believe that controversial creature is probably fictional.
Meanwhile the Trogloraptor is very real and hangs beneath rudimentary webs on cave ceilings.
Its unusual anatomy has forced arachnologists to revise their views of spider evolution.
Scientists said there is strong evidence suggesting that Trogloraptor is a close relative of goblin spiders, but they added that it possesses a “mosaic of ancient, widespread features and evolutionary novelties”.
The true distribution of Trogloraptor also remains unknown at the moment. Scientists believe that while the relatively large, peculiar animal has eluded discovery until 2012, more may be lurking in the forests and caves of western North America.