# Types of Chordata Body Symmetry

Instructor: Margaret Cunningham

Margaret has taught many Biology and Environmental Science courses and has Master's degrees in Environmental Science and Education.

In this lesson, you will explore a group of organisms known as chordates. You'll learn about their general features and also examine what type of symmetry they have.

## Types of Symmetry

Imagine there is only one slice of pizza left that you want to cut equally to share with your friend. When you're cutting the slice, you're trying to maintain symmetry. Symmetry is when something is divided into equal parts or pieces. The concept of symmetry can also be applied to organisms.

Most animals exhibit either radial or bilateral symmetry. Radial symmetry occurs when the parts of an animal or object are arranged around a central axis and if they are divided through the axis they create equal parts on either side. The example below shows that the square has radial symmetry - if you draw a straight line through the center of the square in any direction, you will end up with two equal parts. Cutting a pie into equal slices is also an example of radial symmetry. Bilateral symmetry is when the body or object can be divided into left and right sides that are mirror images of each other. The example below shows that the letter M has bilateral symmetry. When you cut the letter M in half, you end up with exact copies on the left and right sides.

Now, let's go back to that last slice of pizza from the beginning. If you wanted to be fair and have equal size pieces, you would cut the slice lengthwise, creating two equal and mirror image pieces. Cutting the pizza slice in this manner would be an example of bilateral symmetry.

## What Is a Chordata?

Now that we know more about the types of symmetry, let's apply it to the organisms in the phylum Chordata. Members of phylum Chordata are often referred to as chordates, and these organisms share four common characteristics. First, all chordates have nerve cord that runs the length of the body and develops into the brain and spinal cord. The second characteristic that all chordates have is a notochord, which is a flexible rod that is present during early development to help with stability. Pharyngeal slits are the third characteristics shared by chordates. These slits connect the pharynx, or throat, of the organisms to the outside environment. The final characteristic that all chordates share is a postanal tail, which extends beyond the anus during early development. Although every chordate has these four characteristics at one point, not all chordates maintain them throughout their entire lives. Many chordates have these characteristics early in development and, as they grow and change, they lose these features.

There are over 55,000 different species in phylum Chordata, including fish, amphibians, reptiles, birds, and mammals. Humans are considered mammals and are therefore also a part of phylum Chordata. Below are some images of well known chordates, such as bears, mockingbirds, and bullfrogs.

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