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Zoo-ology: Here's looking at you, kid, hippo, frog, etc.

June 12, 2011 at 1:12 a.m.

Spookfish, a ghostly-looking fish with a bizarre eye structure, is adept at gathering light in dark depths of 1 to 2,000 meters.

By Judie Farnsworth

Some animals' eyes are quite remarkable. They may look very different depending on where and how they live.

Hippos' eyes come with built-in goggles. A clear membrane covers the eyes, protecting them from dirt and debris found in the water. Their underwater vision is excellent.

Chameleons have some of the most distinctive eyes in the animal kingdom. Instead of typical eyelids, they have raised cones with tiny openings for the pupils. Each cone moves independently. They can look backward and forward at the same time. Both eyes turn to one point when zeroing in on something. This stereoscopic vision makes judging the distance of a potential meal quite accurate.

Flounders have migrating eyes. In the larval stage, the eyes are on either side of the brain. As flounders grow, they flatten. Living on the ocean floor, this could mean that while one eye would always look up, the other would be in the mud.

Not so with this fish. One of the eyes migrates and both eyes end up on the same side - looking up. Eyes migrating left or right depends on the species type. A whole new meaning to wandering eyes.

The pale eyes and horizontal slit pupils of goats are strange, if not creepy looking. They dilate to nearly rectangular and let the goat see at about a 330-degree angle. Humans generally see about half that.

Actually, most hoofed animals have square pupils, but their eyes are dark and it's not as obvious.

Have you ever watched a frog eating? There's a whole lot of blinking going on. That's because the frog uses its bulging eyes to swallow. It can't chew its food or use its tongue. Froggie pulls its eyeballs into the sockets (closing the eyes). The eyes sink down into the skull and push the food along. Gulp.

Scallops (bivalve mollusks) have eyes with wow factor. There are between 50 to 200 primitive eyes in rows, like a necklace, along the scallop's soft mantle edge. Most astounding, the eyes are bright blue. If an eye is lost or damaged, it will re-grow. These eyes primarily detect motion, light and dark and alert the scallop to close tight or swim away.

The spookfish (real name) is a ghostly looking fish with a bizarre eye structure adept at gathering light in dark depths of one to 2,000 meters. The fish was first noticed 120 years ago, but until 2007, no one had discovered its reflective eyes, because a live animal had never been caught.

Some scientists describe its vision as, like using rearview mirrors. It looks like the fish has four eyes, but there are only two. Each is split into two connected parts. The bottom half points up, to find potential food. The top half (looking like bumps on the side of the head) points down.

The eyes have layers of reflective quanine crystals (these give fish silvery sheens). A focused image is bounced from the reflector areas to the retina. Pretty amazing!

There are endless examples of incredible adaptations in the animal world. Take the time to look for yourself. You'll not be bored.

Judie Farnsworth is a long-time volunteer at the Texas Zoo specializing in educational programs.

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