UV-A-induced movement by flatworm

Decapitated flatworms glide away from a source of ultraviolet light. Credit: Nishan Shettigar


How headless worms see the light to steer

Light-sensitive cells, distributed throughout its body, help a simple creature to do the extraordinary.

Decapitated flatworms can ‘see’ where they’re going, thanks to light-sensitive cells throughout their bodies.

Like most animals, flatworms have eyes that respond to light. But previous research had suggested that the worms could detect and react to light without using their eyes.

Akash Gulyani, now at the University of Hyderabad in India, and his colleagues cut the heads off Schmidtea mediterranea worms and then exposed the bodies to a type of ultraviolet light called UV-A. The headless worms moved away from the light, just like intact worms do.

By looking at gene expression throughout the animal’s tissues, the researchers found that the flatworms’ bodies were lined with networks of light-sensitive cells that coordinate this kind of movement. These cells contained a new type of light-sensitive protein, which was also found in pigment cells in the worms.

Newly hatched worms do not have this light-sensing ability, suggesting that it develops in adulthood. Because flatworms are nocturnal, the authors think the system evolved to help them to quickly hide from the Sun, even if they are resting and not using their eyes or brains.