Radial symmetry

Definition

Radial symmetry is a body plan in which any longitudinal cut through the organism's central axis results in identical halves. This symmetry is commonly found in simple animals like cnidarians and echinoderms.

5 Must Know Facts For Your Next Test

1. Radial symmetry allows organisms to interact with their environment from all directions.
2. Animals with radial symmetry generally have a top and bottom but no left or right sides.
3. Examples of radially symmetrical animals include jellyfish, sea anemones, and starfish.
4. Radial symmetry is often associated with sessile or slow-moving organisms that benefit from sensing their surroundings equally from all sides.
5. In evolutionary terms, radial symmetry is considered more primitive than bilateral symmetry.

Review Questions

• What type of animal body plan divides the organism into identical halves through any longitudinal cut?
• Name three examples of animals that exhibit radial symmetry.
• Why might radial symmetry be advantageous for sessile or slow-moving organisms?

Related terms

Bilateral Symmetry: A body plan where the organism can be divided into mirror-image halves along one plane only.

Cnidarians: A group of animals characterized by radial symmetry, including jellyfish and corals.

Echinoderms: Marine animals such as starfish and sea urchins that exhibit radial symmetry, particularly noticeable in adults.