Most people thought that star fishes don’t have eyes, but these creatures have eyes located at the ends of their arms although are less acute than human eyes. They are historically been thought of as simple animals, because their eyes are also relatively simple and they lack a brain, it was difficult to illustrate how or even if they could see.
About 200 years back researchers knew that most starfish have compound eyes at the end of each arm, their eyes have multiple lenses like insects. Every small lens generates a single pixel of the whole image seen by an animal. Although scientist succeeded about such discovery, they did not test the visual sharpness of starfish eyes. Previously researches show that these creatures can distinguish between day and night although they are not sure whether starfishes can see images or not.
In 2014 Scientists (Anders Garm and his team) revealed that the tropical starfish named Blue sea star (Linckia Laevigata) had eyes with true image formation but with less acute resolution. That low vision helps them to navigate perfectly at the ocean floor. Also in 2016 the same scientists discover another starfish named Acanthaster planci with advanced compound eyes.
Scientist (Garm and his fellows) describe more about the blue sea star, these starfish lives in the tropical pacific and Indian Ocean nearby coral reefs. Scientist found that these creatures cannot differentiate colors as they lack lenses, they see low resolution images.
Starfish cannot recognize small material around them, but the availability of eye on every arm let them to observe well broadly. They can observe stationary and moving materials including coral reefs found within their homes. Researchers (Garm and Nilsson) postulated that starfish use their eyes to prevent drifting very far from their homes (Coral reefs) and beached on sand patches, where will have no protection against predators and cannot find food. The same scientist reveal that these fishes are unable to see colors but the Sea will look blight (light) and coral reefs will look black.
Scientist (Anders Garm and his team) test their postulation about these fishes by performing the following experiment; they locate starfish by three different distances from coral reefs such as one meter, two meter and four meters. The results of this experiment were as follows; at one meter the sea star moves directly to the reef, at two meters starfishes cannot resolve the reef image and will not go further beyond that limit. At four meters they moves in random directions
Although starfishes have eyes some are blind, blinded starfishes will lost completely even at one meter away from coral reefs. Also during the dark moonless night seeing starfishes cannot move further even when placed one meter away from coral reefs. These experiments reveal that starfishes use their eyes to monitor them.
Starfishes found in the deep sea about 1km beneath the water’s surface can still see in spite of the dark as no sunlight can penetrate. These species seeing in the dark have more sensitive eyes though can see coarser images. These Sea stars have clear visual capacity than those found in shallow water where light is available.
Why deep sea starfishes see more clearly that shallow ones? Researchers reveal that some starfishes see more clearly in horizontal direction than vertical direction and some have lower ability to notice changes of what they are sighting over a period of time. Also these two species are also bioluminescent meaning they can generate short radiant flashes through their body surfaces.
In 2016, researchers (Garm and his colleagues) reviewed 13 various starfishes found in deep and shallow water. During that review they discover one starfish named Critter (Ctenodiscus crispatus) which don’t have eyes and live in sediment. These fishes use sense of smell for navigation.
The remained reviewed starfishes (12) have eyes and live in deep sea and other in shallow water, among these twelve two of them (Novodinia americana and Diplopteraster multipes) are bioluminescent meaning they can emit light on their own. Anders Garm added that the glowing starfishes (bioluminescent) use their sight to perceive the radiant signals from other sea star fishes.
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Posted by: Lusubilo A. Mwaijengo
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