In which of the following phyla, the adult shows radial symmetry while the larva has bilateral symmetry?

Options

A. Mollusca
B. Cnidaria
C. Echinodermata
D. Annelida

Answer

To solve the question regarding which phyla have adults that show radial symmetry while the larva has bilateral symmetry, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Symmetry Types**:
- **Radial Symmetry**: Organisms can be divided into similar halves by multiple planes passing through the central axis.
- **Bilateral Symmetry**: Organisms can be divided into two similar halves by a single plane.

2. **Examine the Options**:
- **A. Mollusca**: Members of this phylum, such as snails and clams, exhibit bilateral symmetry in both their larval and adult forms.
- **B. Cnidaria**: This phylum includes jellyfish and corals, which exhibit radial symmetry in adults and do not have a larval stage with bilateral symmetry.
- **C. Echinodermata**: This phylum includes starfish and sea urchins. Their larvae (like the bipinnaria) exhibit bilateral symmetry, while adults show radial symmetry.
- **D. Annelida**: This phylum includes segmented worms, which exhibit bilateral symmetry in both larval and adult forms.

3. **Identify the Correct Phylum**:
- From the analysis, only **Echinodermata** has the characteristic of having larvae with bilateral symmetry and adults with radial symmetry.

4. **Conclusion**:
- Therefore, the correct answer to the question is **C. Echinodermata**.