With a head covered in rows of curved spines, ancient Selkirkia worms could easily be confused with the razor-toothed sandworms that inhabit the deserts of Arrakis in “Dune: Part Two.”

During the Cambrian Explosion more than 500 million years ago, these weird worms — which lived inside long, cone-shaped tubes — were some of the most common predators on the seafloor.