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Science Class 7th grade

Ms. Artigas

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T he balanced arrangement of parts, called symmetry, is

characteristic of many animals. An animal with bilateral

symmetry has a line of symmetry that divides it into halves

that are mirror images.

Animals with radial symmetry have many lines of symmetry 

that all go through a central point. A few animals, including

most sponges, have no symmetry. Depending on their

symmetry, animals share some general characteristics.

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Animals with radial symmetry have body parts that arearranged in a circular pattern around a central point,like spokes on a bicycle wheel.  T hey do not have

distinct front or back ends.

Animals with radial symmetry live in water and do notmove very fast.  T hey either stay in one spot or creepalong the bottom.

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Animals with bilateral symmetry are often

larger than those with radial symmetry. T hey 

have more complex and streamlined bodies. T hese streamlined bodies allow the animals

to move more quickly than animals with

radial symmetry.

T he sense organs of animals with bilateral

symmetry are located at the front end of 

their bodies. Swift movement and sense

organs help animals with bilateral symmetry obtain food and avoid enemies

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Two Matching Sides

Many animals have a body form that is symmetrical,meaning that it could be divided into matchinghalves 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 itsleft half ³ this is called bilateral symmetry (bi  = two,

latus  = side).

Other animals have symmetry like a snowflake·s ³ there are many different ways to carve it intomatching halves, and all of these lines meet in the

middle, dividing it up like a birthday cake.T 

hat iscalled radial symmetry.

Other animals are not symmetrical at all ³ theirbodies cannot be divided into similar halves with astraight line.

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