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The eye is approximately spherical, as is the lens, which is fully internal. Unlike the vertebrate eye, a cephalopod eye is focused through movement, much like the lens of a camera or telescope, rather than changing shape as the lens in the human eye does.
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Unlike the vertebrate camera eye, the cephalopods' form as invaginations of the body surface (rather than outgrowths of the brain), and consequently the cornea lies over the top of the eye as opposed to being a structural part of the eye. Contention exists on whether this is truly convergent evolution or parallel evolution. For the past 140 years, the camera-type cephalopod eye has been compared with the vertebrate eye as an example of convergent evolution, where both types of organisms have independently evolved the camera-eye trait and both share similar functionality. They have a camera-type eye which consists of an iris, a circular lens, vitreous cavity (eye gel), pigment cells, and photoreceptor cells that translate light from the light-sensitive retina into nerve signals which travel along the optic nerve to the brain. 4 is the vertebrate blind spot.Ĭephalopods, as active marine predators, possess sensory organs specialized for use in aquatic conditions. In cephalopod eyes, the nerve fibers route behind the retina, and do not block light or disrupt the retina. Some even make a door for themselves-a rock pulled into place once they’re safely tucked into their homes.In vertebrate eyes, the nerve fibers route before the retina, blocking some light and creating a blind spot where the fibers pass through the retina. Solitary animals, they typically live alone, sometimes in dens they build from rocks, sometimes in shells they pull over on top of themselves. Octopuses mostly feed on crabs, shrimp, and mollusks. Most live on the seafloor, but some, like the paper nautilus, drift nearer to the surface. There are around 300 species of octopus and they are found in every ocean. Another shot a jet of water at a light to cause a commotion. They’ve also can develop opinions about people one routinely squirted water down the back of a keeper it seemed to dislike. Octopuses can open clamshells, maneuver rocks-even dismantle the filtration systems of an aquarium tank. The octopus’s arms are lined with hundreds of suckers, each of which can be moved independently thanks to a complex bundle of neurons that acts as a brain, letting the animal touch, smell, and manipulate objects. If all else fails, octopuses can lose an arm to an attacker and regrow one later. Their soft bodies mean octopuses can fit into impossibly small nooks and crannies, as long as the holes are not smaller than the only hard parts of their bodies: their beaks. Octopuses can also release a cloud of black ink, which obscures them and dulls an encroacher’s sense of smell. If a predator gets too close octopuses can escape quickly, shooting themselves forward by expelling water from a muscular tube called a siphon. They can match the colors and even textures of their surroundings, allowing them to hide in plain sight. Octopuses are highly intelligent animals, masters of camouflage that have evolved an array of tricks over tens of millions of years to avoid or thwart would-be attackers. “Cephalopod” is Greek for “head-foot,” which makes sense, since their limbs are attached directly to their head. They have bulbous heads, large eyes, and eight very useful arms. Octopuses (or octopi, if you prefer) are cephalopods, invertebrates that also include squid and cuttlefish.