Sea Creature Sees Without Eyes
2020-01-09
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1A relative of starfish does not have eyes, but can still see.
2That information comes from scientists who studied sea creatures in the coral reefs of the Caribbean and Gulf of Mexico.
3The researchers reported this month that the starfish relative -- called the red brittle star -- is only the second creature known to be able to see without having eyes.
4This ability is called extraocular vision.
5The other creature said to have extraocular vision is a kind of sea urchin.
6Brittle stars, with five arms extending from a central disk, are part of a group of marine life called echinoderms.
7They have a nervous system but no brain.
8The red brittle star measures up to about 35 centimeters wide, from the end of one arm to the other.
9It lives in bright and complex environments.
10Because of the possibility of being eaten by fish, the creature hides during daylight hours.
11The red brittle star possesses extraocular vision as a result of light-sensing cells, called photoreceptors.
12These photoreceptors cover its body and chromatophores, the cells responsible for pigment or coloring.
13During daytime, the chromatophores narrow the field of light being detected, making each photoreceptor like the pixel of a computer image.
14When combined with other pixels, the image becomes complete.
15The visual system does not work at night, when the chromatophores contract in size.
16Laboratory experiments suggested that the brittle stars have very simple vision.
17Placed in a circular environment, for example, they moved toward walls that were white with a black bar, suggestive of a daytime hiding place.
18Lauren Sumner-Rooney is a research fellow at the Oxford University Museum of Natural History.
19She led the study, which appeared in the publication Current Biology.
20"If our conclusions about the chromatophores are correct, this is a beautiful example of innovation in evolution," she said.
21Sumner-Rooney added, "It's such an alien concept for us, as very visually driven animals, to conceive of how an animal might see its habitat without eyes, but now we know of two examples."
22I'm John Russell.
1A relative of starfish does not have eyes, but can still see. That information comes from scientists who studied sea creatures in the coral reefs of the Caribbean and Gulf of Mexico. 2The researchers reported this month that the starfish relative -- called the red brittle star -- is only the second creature known to be able to see without having eyes. This ability is called extraocular vision. 3The other creature said to have extraocular vision is a kind of sea urchin. 4Brittle stars, with five arms extending from a central disk, are part of a group of marine life called echinoderms. They have a nervous system but no brain. 5The red brittle star measures up to about 35 centimeters wide, from the end of one arm to the other. It lives in bright and complex environments. Because of the possibility of being eaten by fish, the creature hides during daylight hours. 6The red brittle star possesses extraocular vision as a result of light-sensing cells, called photoreceptors. These photoreceptors cover its body and chromatophores, the cells responsible for pigment or coloring. 7During daytime, the chromatophores narrow the field of light being detected, making each photoreceptor like the pixel of a computer image. When combined with other pixels, the image becomes complete. 8The visual system does not work at night, when the chromatophores contract in size. 9Laboratory experiments suggested that the brittle stars have very simple vision. Placed in a circular environment, for example, they moved toward walls that were white with a black bar, suggestive of a daytime hiding place. 10Lauren Sumner-Rooney is a research fellow at the Oxford University Museum of Natural History. She led the study, which appeared in the publication Current Biology. 11"If our conclusions about the chromatophores are correct, this is a beautiful example of innovation in evolution," she said. 12Sumner-Rooney added, "It's such an alien concept for us, as very visually driven animals, to conceive of how an animal might see its habitat without eyes, but now we know of two examples." 13I'm John Russell. 14Will Dunham reported on this story for Reuters. John Russell adapted it for VOA Learning English. George Grow was the editor. 15________________________________________________________________ 16Words in This Story 17coral reef - n. a rocky, underwater area formed by the growth of coral 18extraocular - n. taking place outside the eye 19species - n. a group of living organisms made up of similar individuals 20detect - v. to identify or discover 21pixel - n. any one of the very small dots that together form the picture on a television screen or computer monitor 22contract - v. to decrease in size; shrink 23innovation - n. the act or process of introducing new ideas, devices, or methods 24evolution - n. the development of something, from a simple to a more complex form 25conceive - v. to think of or create (something) in the mind 26We want to hear from you. Write to us in the Comments Section.