It's real. Or was, 300 million years ago, as Ed Yong explains:
A pipe-fitter by trade, Tully was just an amateur collector, but a skilled one. He knew that the coal miners of Mazon Creek had discarded vast piles of shale that contained fossils galore. And as he sifted through the fragments, he found two rocks that had cracked open and that held something incredible between them...There's more at the Atlantic.
Fifty years after Tully’s discovery, he and Richardson have both passed away, and the Tully Monster is the official state fossil of Illinois. And finally, a team of scientists led by Victoria McCoy at Yale University have solved the mystery of the strange beast, and assigned it a spot on the tree of life. It turns out to be a close relative of modern lampreys... Its body is short and stout. Its eyes sit at the end of a rigid bar. And instead of the distinctive sucker, its mouth is a long, triple-jointed claw...
Why, for example, were Tullimonstrum’s eyes at the end of a rigid bar? “We think that the best comparison is to the hammerhead shark,” says McCoy. Their wide-set eyes give them exceptional binocular vision. “We think the eyebar allowed Tully monster to see the things it was grabbing with the mouth at the end of the proboscis.” Oh yes. There’s that. Other scientists had interpreted that weird mouth as a flexible trunk. But since it usually had sharp bends in the same three places, McCoy’s team think it was jointed. It ended in a claw-like mouth, which contained two rows of teeth and could probably open and close. The mouth also contains something that looks like a tongue. Perhaps the whole proboscis is an extremely extended version of the lamprey’s sucker. Lampreys stick to passing fish with their mouths and teeth, while rasping off bits of flesh with their tongues. Perhaps the Tully monster did the same, but at a distance. “It might have been a sort of protrusile, lamprey-like feeding apparatus, like the jawed tongue of the monster in Alien,” says Janvier.