Scientists found a prehistoric ancestor of an arrow worm among a group of fossils at two national parks in Canada.

The fossils were found in what is now British Columbia, but was once an ocean.

The sea worm was 10 centimeters long and had 50 spines on its head. The spines could close suddenly to capture smaller sea creatures, like shrimp.

The scientists reported their discovery in the journal Current Biology in early August.

They are calling the creature Capinatator praetermissus. They say it lived 500 million years ago and is very different from anything alive now.

Capinatator means "grasping swimmer."

Derek Briggs is a scientist from Yale University. He led the expedition. He said the creature was larger than today's similar worms. The arrow worms of today have teeth instead of spines.

Briggs said the worm was probably a good predator because it had so many spines.

The scientists said it is difficult to find evidence of these prehistoric worms because their bodies decayed so quickly. But this discovery was in such good shape, they were able to make a good guess about how the worm looked.

Researchers were able to make a detailed drawing and an animation of how they think the worm moved in the ocean.

Doug Erwin works for the Smithsonian Institution in Washington, D.C. He was not involved in the research. He said the discovery will help scientists better understand the worms and other life from this ancient period.

I'm Dan Friedell.

Dan Friedell adapted this story for Learning English based on reporting by the Associated Press. Caty Weaver was the editor.