Bizarre starfish-like creature with no eyes can see by using light sensors on its body to create a ‘pixel like image’ of its surroundings, a new study finds
- Researchers studied the Caribbean marine species called Ophiocoma wendtii
- Commonly known as the red brittle star, it is related to star fish and sea urchins
- It uses its ability to change its skin colour to turn on and off certain light sensors
- It’s only the second species found to have actual vision – the other is a sea urchin
An eyeless starfish-like creature is able to see by using light sensing cells to create a ‘pixel like image’ of its surroundings, a new study finds.
Researchers from the Oxford University Museum of Natural History studied the Caribbean marine species Ophiocoma wendtii – the ‘Red Brittle Star’.
It was already known that the creature has thousands of light sensing cells across its body, but scientists wanted to find out whether it just sensed light or ‘had vision’.
The team found the creatures do have a form of vision – this is because they were able to seek out areas of contrast when tested rather than just sense light levels.
The team say their tests show that the vision is very rudimentary, but enough for it to be able to spot a safe hiding place during the day.
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An eyeless star fish species is able to see by using light sensing cells to create a ‘pixel like image’ of its surroundings, a new study finds.
They do this by using moving pigment cells – which allow it to change colour from daytime to nighttime – to cover over certain light sensing cells which then restricts the angle of light coming into the light sensors.
Without the ability to cover certain cells, the amount of light coming in would be much greater ‘making vision impossible’, the researchers concluded.
This process of taking small blocks of data and putting them together to create something new is similar to the way pixel images are produced on a computer.
This process of taking small blocks of data is similar to the way multiple tiny single square pixels can produce a detailed image on a computer screen
‘It’s such an alien concept for us, as very visually driven animals, to conceive of how an animal might view its habitat without eyes’, said author Lauren Sumner-Rooney.
‘Although it appears that their vision is very coarse, on the crowded tropical reefs disturbed brittle stars never have to look too far for the nearest cover.’
It is only the second species discovered that has the ability to see without eyes, a phenomenon called ‘extraocular vision’ – the other is the sea urchin.
The brittle stars body is covered in two main types of cells, photoreceptors that sense light and chromatophores that control what colour the creature is.
The chromatophores move during the day, allowing the animal to change its colour from a deep reddish-brown in daytime to a stripy beige at nighttime.
It is up to about 14 inches from arm tip to arm tip and lives in bright and complex habitats, with high predation threats from reef fish.
‘If our conclusions about the chromatophores are correct, this is a beautiful example of innovation in evolution,’ said Sumner-Rooney.
The brittle stars body is covered in two main types of cells, photoreceptors that sense light and chromatophores that control what colour the creature is
When the team placed the creatures in a circular arena, they moved toward walls that were white with a black bar, suggestive of a daytime hiding place.
When they were presented with gray walls making it so no part of the arena was lighter or darker overall, they still moved toward the black stripe, which was centered on a white stripe so as to reflect the same amount of light as the gray.
This species first captured scientific attention more than 30 years ago thanks to its dramatic change in colour between day and night and its strong aversion to light.
Brittle stars have five radiating arms extending from a central disk – they are related to starfish, sea cucumbers, sea urchins and others.
The marine creatures form a group of invertebrates called echinoderms with a nervous system but no brain.
It is only the second species discovered that has the ability to see without eyes, a phenomenon called ‘extraocular vision’ – the other is the sea urchin
Although this is the first visual system that seems to work using whole body colour change, researchers say it is similar to the way a sea urchin can ‘see’ without eyes.
‘Only one species of sea urchin has ‘passed’ the same tests for vision, and it also, independently, changes colour in response to light levels’, the team said.
‘It’s a very exciting discovery,’ explains Sumner-Rooney.
‘It had been suggested 30 years ago that changing colour might hold the key to light-sensitivity in Ophiocoma, so we’re very happy to be able to fill in some of the gaps that remained and describe this new mechanism.’
The research has been published in the journal Current Biology.
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