There are 44 species of the genus Cyclops, also known as water fleas, all with a single eye that is either red or black. Cyclops are between 0.5-3 mm long, have 5 pairs of limbs on the head and another 7 pairs of limbs on the mid-body.
Like sea urchins, hydras also respond to light even though they lack eyes. When scientists sequenced the genome of Hydra magnipapillata, they found plenty of opsin genes. Recently, scientists confirmed that hydras have opsins in their tentacles, specifically in their stinging cells, known as cnidocytes.
In mythology, folklore and religion
Cyclopes (singular: Cyclops), one-eyed giants in Greek mythology, including Polyphemus. They had a single eye in the centre of their forehead. The Graeae, the three witches (or sisters) that shared one eye and one tooth between them; often depicted as clairvoyant.
Polyphemus, in Greek mythology, the most famous of the Cyclopes (one-eyed giants), son of Poseidon, god of the sea, and the nymph Thoösa. According to Ovid in Metamorphoses, Polyphemus loved Galatea, a Sicilian Nereid, and killed her lover Acis.
Odin has many names and is the god of both war and death. Half of the warriors who die in battle are taken to his hall of Valhalla. He is the one-eyed All-Father, who sacrificed his eye in order to see everything that happens in the world. He has two sons, Balder by his first wife Frigg and Thor by Jord.
To date, there's only one species that has been called 'biologically immortal': the jellyfish Turritopsis dohrnii. These small, transparent animals hang out in oceans around the world and can turn back time by reverting to an earlier stage of their life cycle.
Flatworms, nematodes, and cnidarians (jellyfish, sea anemones, and corals) do not have a circulatory system and thus do not have blood. Their body cavity has no lining or fluid within it.
It comes from the coleoid cephalopods, the squids, cuttlefishes, and octopuses. These animals seem to be deaf. Their deafness is so remarkable that it needs to be explained in functional and evolutionary terms.
Lithobates catesbeianus is an animal that cannot sleep.
Interestingly enough, in our versatile animal kingdom, there are multiple animals that are born blind. One of them is the eyeless shrimp, which only has light perception. Another one is the star-nosed mole, the fastest-eating mammal in the world, who uses touch as their main sensory organ.
Taste sensations
Other animals naturally have no tongues, such as sea stars, sea urchins and other echinoderms, as well as crustaceans, says Chris Mah via email.
Earthworms are invertebrates, which means they do not have a backbone. In fact, they don't have any kind of bones, legs, eyes, or teeth.
One species of salamander lacks lungs, so it breathes by absorbing oxygen through its skin and the roof of its mouth.
However, if a kangaroo rat drinks water, the necessary bodily liquids and vitamins are flushed out, and it dies as a result of dehydration.
Bullfrogs… No rest for the Bullfrog. The bullfrog was chosen as an animal that doesn't sleep because when tested for responsiveness by being shocked, it had the same reaction whether awake or resting.
Can you guess what animals might have blue blood? Lobsters, crabs, pillbugs, shrimp, octopus, crayfish, scallops, barnacles, snails, small worms (except earthworms), clams, squid, slugs, mussels, horseshoe crabs, most spiders. None of these animals have backbones. Some of these animals are Mollusks, like the snails.
Reptiles have on a number of occasions evolved into limbless forms – snakes, amphisbaenia, and legless lizards (limb loss in lizards has evolved independently several times, examples include the families Pygopodidae and Dibamidae and species of Isopachys, Anguis, and Ophisaurus).
Bizarrely, many of the ostrich's closest relatives don't have kneecaps at all. In 2014 Regnault showed that emus and cassowaries, and likely the extinct moa, all seem to lack kneecaps.
Spiders do not have a skeleton inside their bodies. They have a hard outer shell called an 'exoskeleton'. Because it is hard, it can't grow with the spider. So young spiders need to molt, or shed their exoskeleton.
A giant anteater's tongue is 2 feet long and can flick in and out of its mouth 150 times per minute. It's coated in sticky saliva, which allows anteaters to slurp up ants and termites. Research has found that giant anteaters can identify a particular species of ant or termite by smell before they rip apart a nest.
All species have different breeds of bacteria that are able to survive in their saliva, so it would be extremely hard to answer the question of which animal has the cleanest tongue. There's a myth that dogs have the cleanest mouth, even cleaner than humans, supported by no scientific evidence.
Now, due to antagonistic fashion in which colours work and the opponent process, we can't see certain colours at the same time, i.e. blue versus yellow, red versus green, and light versus dark. The colours blueish-yellow and greenish-red are the alleged “impossible” colours we can't see.
Red-green and yellow-blue are the so-called "forbidden colors." Composed of pairs of hues whose light frequencies automatically cancel each other out in the human eye, they're supposed to be impossible to see simultaneously.