Idmonarachne brasieri is about as close as you can get to a spider without being a spider. In new research published in Proceedings of the Royal Society B, scientists argue that this newly-described-almost-spider's lack of silk spinnerets hint that web-weaving skills gave true spiders an evolutionary edge.

The not-quite-spider was actually excavated in the 1980s, but the specimen — which was partially hidden by stone that couldn't be removed without damaging its fragile body — has only now been closely examined. Modern imaging technology allowed scientists to create 3-D scans of the animal without splitting it apart, giving them their first real look at its eight-legged form.

Idmonarachne brasieri lived 305 million years ago in what is now France, and researchers believe it can be distinguished as a unique species based on its powerful jaws, which are unlike those found on other proto-spiders from the same period. It has a lot in common with modern spiders: It has eight legs and fangs, and even though it was only about a centimeter across, I'd probably freak out if I saw it in my bathroom. But in addition to a segmented rear-end more typical of pre-spider arachnids, it had one glaringly non-spider-like quality — a lack of spinnerets.

"The earliest known spider is actually from the same fossil deposit — and it definitely has spinnerets," lead author Russell Garwood of the University of Manchester told BBC News. "So what we're actually looking at is an extinct lineage that split off the spider line some time before 305 million years ago, and those two have evolved in parallel."

National Geographic reports that the arachnid may have produced silk, but with less finesse than its more successful cousins. Other non-spider species from early arachnid history had the ability to make the stuff, but not to spin it into webs or use it to wrap up prey. It's possible that these species, including Idmonarachne brasieri, had more rudimentary uses for their silk.

It could be that this made the difference between pre-spider lineages that went extinct and ones that evolved into today's creepy crawlers.

By examining this and other early arachnid fossils, scientists might be able to get a better handle on how the members of this highly successful class actually fit together on their family tree.

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