Secondary radial symmetry occurs in

Options

A. Jelly fish
B. Echinodermata
C. Hemichordata
D. Cnidaria.

Answer

**Step-by-Step Solution:**

1. **Understanding Symmetry Types**: Begin by recognizing the types of symmetry in animals. There are two primary types: bilateral symmetry and radial symmetry. Bilateral symmetry means the organism can be divided into mirror-image halves along one plane, while radial symmetry means the organism can be divided into similar halves around a central axis.

2. **Identifying Echinodermata**: Echinoderms, such as starfish and sea urchins, initially exhibit bilateral symmetry, especially during their larval stages. This means that as larvae, they can be divided into two equal halves.

3. **Evolution of Symmetry in Echinoderms**: Over time, as they develop into adults, echinoderms undergo a transformation where they exhibit secondary radial symmetry. This means that although they start with bilateral symmetry, they develop a radial arrangement in their adult form. This change is a significant aspect of their evolutionary biology.

4. **Comparing with Other Options**:
- **Jellyfish**: They exhibit primary radial symmetry throughout their life cycle, not secondary.
- **Hemichordata**: Members of this group, like acorn worms, show bilateral symmetry.
- **Cnidaria**: Similar to jellyfish, they also display primary radial symmetry.

5. **Conclusion**: Since echinoderms are the only group among the options that exhibit secondary radial symmetry (having evolved from bilateral symmetry), the correct answer is Echinodermata.

**Final Answer**: Secondary radial symmetry occurs in Echinodermata.

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