The orgenism where the adult shows pentaradial symmetry , while the larval forms shows biradial symmetry is

Options

A. Apis.
B. Pleuroblanchia.
C. Antedon.
D. Adamsia .

Answer

To solve the question regarding the organism that exhibits pentaradial symmetry in its adult form and biradial symmetry in its larval form, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Symmetry Types**:
- **Radial Symmetry**: An organism is said to have radial symmetry if it can be divided into equal halves by multiple planes passing through its center.
- **Pentaradial Symmetry**: This is a specific type of radial symmetry where the organism can be divided into five equal parts.
- **Biradial Symmetry**: This type of symmetry allows for division into two equal halves, but only along two specific planes.

2. **Identifying the Organisms**:
- We need to examine the options provided: A. Aepis, B. Pleurobrachia, C. Antidon, D. Adamsia.
- We will look for organisms known to exhibit the specified types of symmetry.

3. **Analyzing Each Option**:
- **Aepis**: This organism does not typically show the required symmetry.
- **Pleurobrachia**: Known for its biradial symmetry as an adult, but not pentaradial.
- **Antidon**: This organism is known to have pentaradial symmetry in its adult form and biradial symmetry in its larval form.
- **Adamsia**: This organism does not fit the criteria for the specified symmetries.

4. **Conclusion**:
- Based on the analysis, the organism that exhibits pentaradial symmetry in adults and biradial symmetry in larvae is **C. Antidon**.

### Final Answer:
**C. Antidon**