If you look closely at a modern spider (sorry, arachnophobes), the entire back half of the body is a single bulbous structure. “Not so in this creature!”, Garwood says of Idmonarachne. The ancient invertebrate retains segments along its abdomen, more like archaic forms of arachnids such as the pseudoscorpions.source: http://news.nationalgeographic.com/2016/03/160329-creepy-new-fossil-origins-spiders/
A beautifully preserved fossil from France has given paleontologists a look at an animal that is almost, but not quite, the earliest known spider.
The eight-legged creature lived 305 million years ago and has been named Idmonarachne brasieri, a reference to Idmon, the father of the skilled weaver Arachne in Greek mythology. Amateur fossil hunter Daniel Sotty discovered it in the ancient rock of Montceau-les-Mines in eastern France, and it was later placed in the collections of the Muséum National d’Histoire Naturelle in Paris.
“When I first saw it, I was unsure what kind of arachnid it was,” says University of Manchester paleontologist Russell Garwood. Only the abdomen was visible in the sample, but already Garwood could see hints of a relationship with arachnids. Later, when his team created high-resolution CT scans, they found far more preserved in the Carboniferous-age stone.
“The legs and entire front half of the body was buried in the rock,” says Garwood, whose team describes the fossil this week in Proceedings of the Royal Society B. His team created a 3D model and restoration of Idmonarachne that revealed various arachnid traits, including very spider-like fangs. But the detailed models also highlighted some significant differences.