The adult ……... are radially symmetrical but larvae are bilaterally symmetrical .
(a) Asterias
(b) Balanoglossus
(c) Obelia
(d) Ascaris

Options

A. Asterias
B. Balanoglossus
C. Obelia
D. Ascaris

Answer

To solve the question, we need to identify which organism has adults that are radially symmetrical while their larvae are bilaterally symmetrical. Let's analyze each option step by step.

### Step 1: Understand the Symmetry Types
- **Radial Symmetry**: Organisms can be divided into similar halves by multiple planes passing through the central axis. Example: Starfish.
- **Bilateral Symmetry**: Organisms can be divided into two equal halves only by one plane. Example: Humans.

### Step 2: Analyze Each Option
1. **Asterias (Starfish)**:
- Adults: Radially symmetrical.
- Larvae: Bilaterally symmetrical.
- Conclusion: This matches the description in the question.

2. **Balanoglossus**:
- Adults: Bilaterally symmetrical.
- Conclusion: This does not match the description.

3. **Obelia**:
- Adults: Radially symmetrical.
- Larvae: Also radially symmetrical.
- Conclusion: This does not match the description.

4. **Ascaris**:
- Adults: Bilaterally symmetrical.
- Conclusion: This does not match the description.

### Step 3: Conclusion
After analyzing all the options, the only organism that fits the criteria of having adults that are radially symmetrical and larvae that are bilaterally symmetrical is **Asterias**.

### Final Answer
(a) Asterias