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

Options

A. Annelids
B. Arthropods
C. Molluscs
D. Echinoderms

Answer

To solve the question "In which of the following phyla does the adult show radial symmetry while the larva has bilateral symmetry?" we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Symmetry Types**:
- **Radial Symmetry**: This means that the organism can be divided into similar halves by multiple planes. An example is a starfish.
- **Bilateral Symmetry**: This means that the organism can be divided into two equal halves only by one plane. An example is a butterfly.

2. **Analyze the Options**:
- **A. Annelida**: Members of this phylum, like earthworms, exhibit bilateral symmetry throughout their life cycle.
- **B. Arthropods**: This phylum, which includes insects and crustaceans, also shows bilateral symmetry in both larvae and adults.
- **C. Molluscs**: Molluscs, such as snails and clams, primarily exhibit bilateral symmetry in both their larval and adult forms.
- **D. Echinoderms**: This phylum includes organisms like starfish and sea urchins. Echinoderms have bilateral symmetry in their larval stage and radial symmetry in their adult stage.

3. **Identify the Correct Answer**:
- Based on the analysis, the phylum that fits the criteria of having adults with radial symmetry and larvae with bilateral symmetry is **Echinoderms**.

4. **Conclusion**:
- Therefore, the correct answer to the question is **D. Echinoderms**.