No one suspected that the sea worm and the “seaweed” shared any connection.

“Who’d have ever expected something which people thought was seaweed was actually a tube,” said Simon Conway Morris, a paleontologist at Cambridge University and an author of the study. “And who would have thought this interesting type of worm would build a tube?”

The link came in 2014 when a team of paleontologists from Britain and Canada made a finding that cemented a connection between the two seemingly dissimilar fossils.

Karma Nanglu, a paleobiologist and graduate student at the University of Toronto, was exploring the Burgess Shale Formation in the Canadian Rockies with his colleagues when they uncovered several fossilized tubes in slabs of rocks. Looking closer, they noticed that the cylinders weren’t empty.