Extraocular Vision | 04 Jan 2020

For the first time, researchers have shown that a species of brittle stars can see even though it does not have eyes.

The ability to see without eyes is known as extraocular vision.
The red brittle star (Ophiocoma wendtii) has become only the second creature, after a sea urchin species, known to have the extraocular vision (barring rare cases in other species).
In sea urchins and brittle stars, researchers suspect that extraocular vision is facilitated by the photoreceptor cells found on their bodies.
The researchers suggest that a brittle star sees with the help of light-sensing cells that cover its entire body. These light-sensing cells give the brittle star visual stimuli, allowing it to recognise coarse structures such as rocks.
Another peculiar feature of the red brittle star is its signature colour change. While the creature is deep red during the day, it changes its colour to beige at night.
The researchers think that there may be a link between their extraocular vision and colour changing abilities since the responses they saw in the creatures tested during the day, disappeared in those that were tested at night.