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Marine worm with outstanding vision fascinates researchers

The large-eyed bristle worm Vanadis has long been of interest to the world’s vision researchers. But the worm has been difficult to study since it lives in the open sea and is active at night. Now, a research team has succeeded in locating an Italian worm colony and is able to confirm that the worm has a completely unique vision.

Bristle worms are a group of annelid worms that mostly live in the sea. Their scientific name, Polychaeta, means “many bristles” and refers to the stiff bristles on the worms’ bodies. There are around 14,000 species of bristle worms, and they can be divided into three main groups. For researchers, species that live in open water far from land are of extra interest. They have extremely large, onion-shaped eyes made up of tens of thousands of cells, and they possess both a retina and a lens.

In the past, studying these creatures’ eyes has been difficult, since they are fragile, hard-to-find creatures that live far out to sea. A research team led from Lund, Sweden and Copenhagen, Denmark have now succeeded, however. In a study published in the scientific journal Current Biology, researchers have been able to confirm that the worm has exceptional vision that bears comparison to the sharp-sighted troika of mammals, arthropods and cephalopods. This applies both to the speed at which the bristle worm can see objects move, and how well they see detail. Researchers also investigated how the eye is structured.

A worm with many protrusions alongside its body. Photo.
Bristle worm Vanadis (Photo: Michael Bok)

“Through our investigations, which have included the use of synchrotron radiation in Switzerland, we have succeeded in mapping out the optical characteristics of the worm eye. After studying the spatial and temporal resolution, i.e. pixels in the field of view and frames per second, we found that the worm has high-resolution vision,” says Michael Bok, biology researcher at Lund University.

The team finding a large worm colony relatively close to shore was pure chance. Thanks to a YouTube video recorded by a diver off Ponza, the researchers travelled to Italy and were able to dive at night a depth of a few metres and suck up a quantity of worms into a large plastic wine container.

“They are very delicate animals that get injured and stressed by being caught in plankton nets. So, it was fantastic to land large numbers in perfect condition that we could work with later,” says Michael Bok.

A diver seen against the surface. A blurry photo.
How the bristle worm sees the world (Image: Michael Bok/Megan Porter)

Despite this scientific breakthrough on bristle worms' sharp vision, a number of mysteries around the marine worms’ eyes remain. The researchers still don’t know why these primitive creatures have developed clear vision, or what they use it for.

“It may be for discovering prey, finding each other or visually communicating with each other at night using bioluminescence, i.e. glowing in the dark through a natural chemical process. We hope to be able to answer that question after more visits to Ponza,” says Michael Bok.

As well as Lund University, the University of Copenhagen and the University of Tuscia worked on the study.

The article “High-resolution vision in pelagic polychaetes” is published in Current Biology.