Animal Symmetry

Lesson Plan - Get It!

Audio:

While symmetry may be familiar as a math concept, it is also found in nature.

"Symmetry" means the shape or organism can be divided into parts that are similar across an axis. Notice how three of the four images below can be divided evenly, but the last one is asymmetrical because it cannot be divided evenly:

_{Image by Loggie, via Wikimedia Commons, is in the public domain.}

There are a lot of examples of symmetry in the animal kingdom! In this lesson, you will learn about different body plans that utilize forms of symmetry.

There are three main types of symmetry organisms and animals use: spherical, radial, and bilateral. Symmetry patterns have been important in classifying organisms and animals into Kingdoms, Phyla, Orders, and Classes. If you want to learn more, explore the Elephango lesson on taxonomy found under Additional Resources in the right-hand sidebar.

Spherical symmetry occurs in very small organisms, like algae and protists. These are not classified as animals, but do possess a basic form of symmetry. For these organisms, they can be divided along any plane running through the center of the organism. Volvox is algae that lives in a spherical colony. This organism is a great example of spherical symmetry because it can be divided in many ways, shown below:

Notice how the spherical shape allows for division in several ways, showing spherical symmetry. Most organisms and animals are not spherical in nature, and cannot demonstrate spherical symmetry. Radial and bilateral symmetry are more common forms seen in nature.

Radial symmetry occurs when an organism can be divided along a plane within a circle:

Notice how both organisms can be divided into sections in a circular shape.

Are all creatures circular in shape? Can you think of some creatures that have symmetry but not circular? Humans! We have bilateral symmetry because our right and left halves are very similar. In bilateral symmetry, organisms can be divided into two matching halves along a single plane:

Notice how both organisms show bilateral symmetry? Animals with symmetrical body patterns develop in similar ways from fertilization and an embryo. The symmetry allows us to group and compare organisms, but do all animals have symmetry? Can you think of an asymmetric organism or animal? There are not very many asymmetrical animals, but all sponges are considered asymmetrical. Did you know sponges are actually alive!

Symmetry is just one of the ways we classify and compare living things, but it can be very helpful in grouping animals for study. Microscopic organisms can have spherical symmetry, because they are able to be divided along many planes running through the center of the organism. Most animals follow radial or bilateral symmetry patterns. Radial symmetry occurs when the organism or animal is circular and can be divided along a mid-point. Bilateral symmetry occurs when the organism or animal can be divided into two sides, like left and right.

Not all animals have symmetry, so it is important to be able to identify asymmetry, too!

Discuss what you have learned with a parent or teacher before practicing your identification skills in the Got It? section of this lesson.