An example of a radially symmetrical organisms is

1. Analyze the question The question asks which organism is radially symmetrical. That means the body can be divided into similar halves along any plane that passes through the central axis, like the spokes of a wheel or a pizza cut in many ways.

2. Explain the concept Animals show three main body plans:

• Radial symmetry: The body is arranged around a central axis. Examples are cnidarians (Hydra, jellyfish, sea anemone) and echinoderms (starfish).
• Bilateral symmetry: The body can be divided into two mirror-image halves along only one plane. Examples are flatworms, roundworms, insects and humans.
• Asymmetry: There is no regular body shape, as in most sponges.

3. Solution: check each option

• A. Planaria is a free-living flatworm (Platyhelminthes). It is bilaterally symmetrical.
• B. Hydra is a cnidarian (Coelenterate). Its tubular body has tentacles arranged around the mouth, and it is radially symmetrical.
• C. Tapeworm is a parasitic flatworm (Platyhelminthes). It is bilaterally symmetrical.
• D. Roundworm is a nematode. It is bilaterally symmetrical.

Only Hydra has radial symmetry.

4. Answer Option B: Hydra

5. Exam tip Remember: "Cnidarians and Echinoderms are Circular (radial)". Hydra, jellyfish, sea anemone and starfish are radial. Almost every "worm" in the options, such as flatworms and roundworms, is bilateral. If you see Hydra among the options in a symmetry question, it is usually the answer.