Ancient Sea Spider Related to Scorpion

The fossil of an ancient sea spider thought to be related to modern scorpions has been discovered near Herefordshire in the UK.

The 425-million-year-old creature was encased and preserved in volcanic ash.

Sea spiders are soft-bodied arthropods common in oceans today. Biologists have long wondered about the relationship between them and land spiders. They share similar body forms, but a sea spider has a long proboscis and unusual limbs used in mating and carrying embryos.

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Sea spiders are delicate, so few of their fossils exist.

"This is the earliest adult fossil example, and it is preserved in extraordinary detail," said Derek Briggs, a professor of geology and geophysics at Yale. "Volcanic ash that trapped ancient sea life in this location rapidly encased the creatures making a concrete-like cast of the bodies. The cavity later filled in with carbonate solids so we have a fossil record to study now."

The specimens were sliced up, with digital images taken with every slice. Then the spider was reconstructed with computer graphics. The reconstruction -- revealing large pincers -- suggests Haliestes dasos, as the species is now named, is indeed related to land spiders, scorpions, mites and ticks.

The discovery was reported in today's issue of the journal Nature.