Aug 16, 2007
The fossils from France are 160 million years old
The eight-legged marine animals, which are known as pycnogonids, are only distantly related to land spiders.
The stunning specimens were discovered in 160 million-year-old fossil beds at La Voulte-sur-Rhone, near Lyon in south-eastern France.
Details of the finds are published in the journal Proceedings of the Royal Society B.
Sea spiders are still with us today; scientists have described about 1,300 species of pycnogonid. They are characterised by eight extremely long legs and a prominent mouthpart.
While they may resemble land spiders, the pycnogonids form a distinct biological group.
Writing in Proceedings B, Sylvain Charbonnier from the University of Lyon, France, and colleagues say the new fossils fill a 400 million-year gap in our knowledge of these enigmatic creatures.
The team identified 70 sea spiders from three distinct species in rock slabs from the Jurassic La Voulte Lagerstatte. A Lagerstatte is a sedimentary rock bed rich in fossils or containing well-preserved specimens.
"This Lagerstatte is very important because during Jurassic times the water here was about 200m deep," Mr Charbonnier told the BBC News website.
Many other Lagerstatten from the Mesozoic - the era of the geological time when the dinosaurs walked the Earth - were formed from lagoons or relatively shallow bodies of water. This means that La Voulte Lagerstatte preserved many fossil creatures not found elsewhere.