Starfish Have Poor Vision, Are Color Blind
Anders Lydik Garm
Linckia laevigata, a species of starfish commonly found in the tropical waters of the Indian Ocean and the western and central Pacific Ocean, have relatively poor vision and cannot differentiate between different types of light.
Kay-africa, Wikimedia Commons
Animals and insects see the world in unique ways. From fish, to dogs, to birds to shrimp, super-eyesight allows them to thrive in places others can't.
Dung beetles, for example, have internal compasses that are sensitive to the sun, Marie Dacke of Lund University and her colleagues have determined. In a paper published in the latest Philosophical Transactions of the Royal Society B, she and her team explain that solar cues and skylight help guide where the beetles roll their coveted balls of poop.Video: 5 Incredible Insect Superpowers
shmoomeema, Wikimedia Commons
Siberian huskies evolved colorful, almond-shaped eyes to see in low light, desolate northern regions. A quirk of genetics is that an individual dog may have two differently colored eyes. A single eye may also feature two colors. It's known as a "parti" or "split" eye.Photos: Ugliest Dog Contenders
Chameleons can rotate and focus their eyes separately to look at two different objects at the same time, according to the San Diego Zoo. This gives chameleons a full 360-degree view around their body.Photos: Chameleon Colors Act Like a Mood Ring
Ants have vision "superpowers," interactive media designers and artists Chris Woebken and Kenichi Okada believe. Using their ant apparatus, humans can see as ants do by placing microscope antennas on their hands (ants have these on their heads) that transmit a 50-fold magnified view of wherever the person's hand is resting.33 Bizarre New Ant Species Discovered
Imagine if you spent most of the day looking up from below. That is what escolar, a large and mysterious deep-sea fish, do, according to a new study by Eric Warrant of the University of Lund and colleagues. Escolar use this technique to "sit and wait" for prey, hoping something tasty will swim over them.
Tomasz Sienicki, Wikimedia Commons
Shrimps have some of the most complex visual systems in the animal kingdom. Justin Marshall of the University of Queensland and his team found that some shrimp stare down prey before attacking with a movement that is so swift that it actually boils water in front of the shrimp. (The other temperate water surrounding the shrimp prevents it from cooking itself to death!)
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Most animals, including humans, have round pupils, but the eyes of goats (toads, octopi and a few others too) tend to be horizontal and rectangular with rounded corners. This broadens the horizon that they see, enabling them to better spot predators.
Pen Waggener, Flickr
Bird eyes, such as those of the eagle seen here, feature oil droplets located in the front, Doekele Stavenga of the University of Groningen and colleagues have discovered. The droplets serve as "microlenses" that help to filter and direct light.On the Hunt for Bald Eagles
The eyes of certain animals, such as raccoons and cats, glow in the dark. Their eyes have a light-reflecting surface, known as the tapetum lucidum, which makes this possible. Depending on the animal, the glow takes on certain colors. Cats tend to have eyes that glow green. Miniature schnauzer eyes will sometimes glow turquoise, according to Colorado State University ophthalmologist Cynthia Powell.
Alexander Vasenin, Wikimedia Commons
Cuttlefish, a type of mollusk, are the transformer visionaries of the animal kingdom. They reshape their entire eyes to adjust to what they see. Humans and many other species, in contrast, usually just reshape their eye lenses to get a better look at something.
Giant squid have the largest eyes in the world, according to the Smithsonian National Museum of Natural History. At up to 10 inches in diameter, the human head-sized eyes help giant squid to see in deep water. It's believed that they can detect a moving sperm whale from 394 feet away.Giant Squid Photos
Fernando Mafra, Fotopedia
We create a mental map of our surroundings in our brain. As Michael Land of the University of Sussex explains, "To interact with objects in the world we need to know where they are, whether they are in our field of view or outside it. Objects in memory have to move in the brain as we move through the world, otherwise they would be not be in the right place."
Starfish may have the incredible ability to regenerate their limbs, but when it comes to the power of sight, these marine creatures fall a bit short, a new study finds.
Researchers at the University of Copenhagen in Denmark studied the eyes of Linckia laevigata, a species of starfish commonly found in the tropical waters of the Indian Ocean and the western and central Pacific Ocean; they discovered these sea stars are color-blind and have relatively poor eyesight.
"We studied their spectral sensitivity, meaning what colors of light they see, and found that they don't have color vision," said study lead author Anders Garm, an associate professor in the department of biology at the University of Copenhagen. "Since they can't distinguish between different types of light, they basically see everything in grayscale." (Vision Quiz: What Can Animals See?)
The researchers also found that starfish do not see sharp, clear images. In fact, their eyes have resolutions of only about 200 pixels, Garm told LiveScience. In comparison, most digital cameras have resolutions measured in millions of pixels, or mega-pixels. Human eyes, on the other hand, have roughly 1 million nerves, and a combined total of 120 million rod and cone cells, to see the world in vibrant detail.
Starfish also process images at a much slower rate than humans, which means they are unable to see fast-moving objects, Garm added. For visual systems, this can be measured in hertz, which is a unit of frequency signifying the number of cycles per second of a periodic phenomenon.
"When it comes to the speed of vision, humans typically see things changing at a rate of about 30 to 40 hertz," he said. "With these starfish, we're talking about one to two hertz. This all goes to show that these animals sample a lot less information at any given time than we do."
Yet despite having poor eyesight, starfish eyes are well-suited for their specific needs in the marine environment.
"In terms of evolution, animals only evolve senses as advanced as they need," Garm said. "The vision of the starfish is enough to get it through the things it has to do; they have the exact eyes they need, so to speak."
Linckia laevigata, a species of starfish commonly found in the tropical waters of the Indian Ocean and the western and central Pacific Ocean, have relatively poor vision and cannot differentiate between different types of light.Anders Lydik Garm
Starfish lack a centralized brain, and are thought to have a dispersed nervous system in which each arm essentially has its own brain. This so-called "decentralized nervous system" could explain why starfish eyes have low spatial and temporal resolution.
"It's not surprising that starfish don't see sharp, detailed images, because that would require much more brain power than they have," Garm said. "From an information processing point of view, it would be a waste of energy if they had much better vision."
Still, the researchers were able to demonstrate that starfish use their visual systems to recognize and navigate toward their habitats, Garm said.
"The eyes will optimize the contrast between the coral reef they live on and the open ocean," he explained. "This means if they are crawling around on the reef and suddenly get displaced, they can see the reef and move back toward it so they don't starve."
Garm and his colleagues tested this hypothesis with navigation experiments with regular starfish and ones that had been blinded.
"When we displaced the starfish from the reef onto a sand flat, the ones who had intact eyes moved straight back, whereas the blinded ones walked at the same pace but in random directions," Garm said.
The researchers are now expanding their research to include 20 different species of starfish, and they suggest these different types of sea stars may have similar visual systems. The scientists also intend to examine features of the starfish's visual system — such as individual photoreceptors — in more detail.
The new findings were published online today (Jan. 7) in the journal Proceedings of the Royal Society B: Biological Sciences.