Understanding Evolution

Bilateral (left/right) symmetry

One character inherited by all arthropods is bilateral symmetry.

Two Matching Sides
Many animals have a body form that is symmetrical, meaning that it could be divided into matching halves by drawing a line down the center. In this respect, arthropods are built like humans are; the right half of an arthropod is a mirror image of its left half — this is called bilateral symmetry (bi = two, latus = side). Other animals have symmetry like a snowflake’s — there are many different ways to carve it into matching halves, and all of these lines meet in the middle, dividing it up like a birthday cake. That is called radial symmetry. Other animals are not symmetrical at all — their bodies cannot be divided into similar halves with a straight line.

different types of symmetry

Try it out!
Which of these animals have bilateral symmetry?

 

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http://evolution.berkeley.edu/evolibrary/article/arthropods_04

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