Scientists have discovered a brand new species of spider, with a feature that's not normally seen in the creatures – a tail. If that's making your skin crawl, you can probably take solace in the fact that the arachnid, dubbed Chimerarachne, lived 100 million years ago, and its remains were found trapped in amber in Myanmar.

Amber can give us an unprecedented view into prehistoric life, preserving softer elements that regular fossilization just can't. In the last few years, we've seen some incredible finds inside amber, including a tick in the middle of a meal, an otherworldly insect, a bug that's jumped out of its skin, mammalian red blood cells, and a dinosaur tail complete with feathers.

The Chimerarachne looks an awful lot like a spider: it has four pairs of walking legs, fangs, silk-spinning spinnerets at the rear, and pedipalps at the front. But of course, the eye-catching thing is its long, whip-like tail. Four specimens have been recovered, all of which have bodies about 2.5 mm (0.1 in) long and tails about that long again.

While no living spider species has a tail, the feature isn't unheard of in the arachnid world. Vinegaroons, or "whip scorpions", are close living relatives of spiders that sport tails, and the same research team has previously discovered older arachnids with tails but no spinnerets.

That means Chimerarachne neatly plugs a hole in arachnid evolution. The previous discovery dated as far back as the Devonian period, some 380 million years ago, while the latest find is only about 100 million years old, from the mid-Cretaceous.

"The ones we recognized previously were different in that they had a tail but don't have the spinnerets," says Paul Selden, co-author of a study describing the new species. "That's why the new one is really interesting, apart from the fact that it's much younger — it seems to be an intermediate form. In our analysis, it comes out sort of in between the older one that hadn't developed the spinneret and modern spider that has lost the tail."

It's preserved pretty well, but the researchers can't elaborate too much on the spider's behavior. Given it was encased in amber, Chimerarachne must have lived on or around tree trunks, and like its modern counterparts it most likely would have fed on insects. Although its spinnerets indicate it could produce silk, the scientists don't think it was building elaborate webs for catching prey.

"Spinnerets are used to produce silk but for a whole host of reasons — to wrap eggs, to make burrows, to make sleeping hammocks or just to leave behind trails," says Selden. "If they live in burrows and leave, they leave a trail so they can find their way back. These all evolved before spiders made it up into the air and made insect traps. Spiders went up into the air when the insects went up into the air. I presume that it didn't make webs that stretched across bushes."

Before getting too comfortable, arachnophobes should note there's a chance that tail-sporting descendants of Chimerarachne could still be alive in the jungles of Southeast Asia today, according to the researchers. It is a tiny creature after all, and that habitat hasn't been all that well-explored.

The research was published in the journal Nature Ecology & Evolution.

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