• Illustration detail of Capinatator praetermissus

    Illustration detail of Capinatator praetermissus. (Drawing: Marianne Collins © Royal Ontario Museum)

  • (Image courtesy of the Royal Ontario Museum)

A small marine predator that once snatched its prey from the ocean bottom using a crown of 50 spines has been recently identified by scientists in B.C. The ancient worm, Capinatator praetermissus, represents both a new genus and species.

At about ten centimeters in length, Capinatator is around ten times longer than its modern relatives. Capinatator is also distinctive in that it has twice the number of spines on its head than most similar worms of today. Thought to have lived on the ocean bottom, the newly identified species belongs to a phylum of arrow worms, or Chaetognatha (meaning bristle-jaw) that make up a significant portion of plankton and the lower tier of the oceanic food chain. Around 120 different species of these marine worms exist today.

Information about the new species was gleaned from around 50 fossils found in the Burgess Shale in British Columbia – one of the world’s richest fossil depositories. The Capinatator fossils are over 500 million years old and date to the Cambrian Period, a time known for its wide diversification of animals. The species, described in a study published in the journal Current Biology, suggest that arrow worms started off as larger, benthic predators and later miniaturized and adopted a planktonic lifestyle. 

Since arrow worms are soft-bodied, well preserved fossils from this phylum are scant, making studying the ancient organisms difficult. 

“The fossil record of this group of organisms is very sketchy to say the least,” says study co-author Jean-Bernard Caron, a University of Toronto professor and senior curator of invertebrate palaeontology at the Royal Ontario Museum. The only other fossils of arrow worms come from China. 

The well-preserved specimens from the Burgess Shale provide researchers new insight on the evolution of these organisms, and show a snapshot of what ancient arrow worms would have looked like.