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Tags Current Affairs

Extraocular vision

Date: 04 January 2020 Tags: Biodiversity

Issue

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

 

Background

The red brittle star (Ophiocoma wendtii), which lives in the coral reefs of the Caribbean Sea, becomes only the second creature, after a sea urchin species, known to have this ability.

 

Details

  • The ability to see without eyes is known as extraocular vision. Previous researchers have defined it as the ability to resolve scenes without discrete eyes.

  • In sea urchins and brittle stars, researchers suspect that extraocular vision is facilitated by the photoreceptor cells found on their bodies.

  • 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.

Red brittle star

  • Brittle stars, with five radiating arms extending from a central disk, are related to starfish (also called sea stars), sea cucumbers, sea urchins and others in a group of marine invertebrates called echinoderms. They have a nervous system but no brain.

  • Its photoreceptors are surrounded during daytime by chromatophores that narrow the field of the light being detected, making each photoreceptor like the pixel of a computer image that, when combined with other pixels, makes a whole image. The visual system does not work at night, when the chromatophores contract.

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