Question

If you cut Planaria vertically, you will get two equal halves. What does this indicate?

• A. The organism is asymmetrical.
• B. The organism is radially symmetrical.
• C. The organism is bilaterally symmetrical.
• D. The organism is bi-radially symmetrical.

Answer 1

The correct option is C The organism is bilaterally symmetrical.

• Bilateral symmetry: If an organism is cut through the central axis of any one plane of its body, the resulting halves would be identical. E.g., Planaria, Liver fluke, etc.
• Radial symmetry: When an organism is cut through the central axis at any plane, both the halves will show the same design. Eg., Starfish.
• Asymmetry: Organisms will not show symmetry. E.g., Euplectella, Sycon, Sponges, etc.
• Bi-radial symmetry is found in organisms which show morphological features of both bilateral and radial symmetry. Bi-radially symmetrical organisms can only be cut equally along two planes. E.g., Hydra.