The bodies of worms can seem very uninteresting - and can also be quite repulsive to some people.
However, a closer look reveals curious details about some species of worm.
For example, there are some strange marine worms that protrude their tails with brains to mate.
In a new study, scientists have now discovered that a species of bristle worm, called Vanadis, is equipped with a complex vision system, dominated by two very, very large eyes. They're huge! If humans had eyes that big, they would weigh more like 100 kilos.
In the course of the study, a team of researchers from the University of Copenhagen in Denmark, Lund University in Sweden and the University of Tuscia in Italy examined three species of bristle worms collected by hand in shallow waters.
Their findings were presented in an article published this week in the journal Current Biology.
Vanadis eyes can use ultraviolet light to communicate and find partners or food - a behavior that has not yet been properly documented or studied in the wild.
These worms may also be among the few known bioluminescent animals that use UV light to glow. The bioluminescence of our familiar fireflies, for example, originates from chemical reactions in the insect's abdomen.
The Vanadis studied were found off the coast of the island of Ponza in the Mediterranean Sea, west of Naples in Italy. They belong to a family of large-eyed bristle worms called polychaeta.
They are about 15 centimeters long and feed mainly on plankton, algae and bits of organic matter from dead organisms. The pair of eyes of these worms weighs about 20 times more than the rest of their head, and look like two giant red globes attached to the body.
The authors of the study analyzed the worms in the laboratory and discovered that Vanadis' vision is better and more advanced than previously thought. Their eyes can see very small objects and follow their movements, despite having a simpler nervous system.
The team is still trying to understand how these creatures developed such keen eyesight. Their bodies are transparent, except for their eyes, which need to register light in order to function properly.
According to the researchers, some aspect of having a transparent body with visible eyes must have had evolutionary benefits that outweigh the consequences.
"No one has ever seen these worms during the day, so we don't know where they hide. So we can't rule out that its eyes are also used during the day," says Anders Garm, a neurologist at the University of Copenhagen, in a statement published in EurekAlert.
"What we do know is that the Vanadis' most important activities, such as finding food and mating, take place at night. We believe that part of the explanation lies in the fact that these worms can see different wavelengths of light than humans," explains Garm.
"Like many birds, reindeer and other more complex organisms, Vanadis' eyes can see UV light that is invisible to the human eye. This may indicate that the purpose of the eyes is to see bioluminescent signals in the pitch-black sea," adds the researcher.
"We think that the worms themselves are bioluminescent and communicate with each other through light. If we use normal blue or green light as bioluminescence, we run the risk of attracting predators," explains Garm.
"But if, instead, the worm uses UV light to communicate, itbecomes invisible to animals other than its own kind. So our hypothesis is that they have developed clear UV vision in order to have a secret language related to mating."
That explains it. At the end of the day, the important thing is to ensure the continuation of the species.
