Both sides of this batfi sh look alike.
Seeing Double T e batfi sh has a kind of symmetry called bilateral symmetry. It’s also called mirror symmetry. T at’s because it’s like looking in a mirror and seeing your ref lection. An exact copy of you looks back. In nature, both sides aren’t always exactly
the same. You can see that if you draw a line of symmetry down the middle of your face. You might notice that one eyebrow is slightly higher than the other. Maybe when you smile, you’ve got only one dimple instead of two. Both sides of your face are almost alike, though.
Look at this funny fish. Its red lips
frown. Its eyes glare. It even has a tiny fishing rod hidden in its head. It uses this body part to catch dinner. If all this isn’t odd enough, check out its fins. It’s standing on them. Even though a batfish can swim, it oſt en walks on its fins. A walking batfish may be one of the weirder
critters in the sea. Yet in one way, it’s not odd at all. Like most animals, both sides of its body look about the same. T at makes this strange fish a great example of symmetry. Symmetry occurs when an object has at least
two sides that look alike. Each side has parts that are similar in size and shape. Sometimes, the matching parts are evenly placed along a line. T e line divides the object exactly in half. Sometimes, the matching parts are evenly spaced around a central point. Either way, it’s symmetry. Here’s how you can tell that the batfish is
symmetrical. Draw an imaginary line down the middle of the fish’s face. Each side has a bulging eye, two fins, and half a fishy frown. Both sides look the same.
4 NATIONAL GEOGRAPHIC EXTREME EXPLORER
Making Matches It’s even easier to see this kind of symmetry in a luna moth. Since they zip around, you have to find one resting with its wings open. T en you can really see its symmetry. A pair of pale green wings grows from each
side of the luna moth’s body. Two feathery antennae stick up, one for each side of its head. Its parts are about the same size and shape. T ey are evenly arranged along its furry body. Now look at the color patterns on its wings.
T e spots look like a pair of eyes staring at you. A ribbon of purple runs along the edges of its wings. T e pattern on the leſt side matches the pattern on the right side. It takes thousands of tiny overlapping scales to create these symmetrical patterns. You can find other examples of bilateral
symmetry all around you. Most animals have it. Just look at your pet, a bird, or a salamander. It’s not just in animals. You can find this
kind of symmetry in other places, too. Pluck a leaf. A thick vein runs down the middle and divides the leaf in half. Both sides of the leaf look alike. It’s the same with a bleeding heart f lower. Its curvy petals form a heart shape. Each half of the heart looks the same.
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