A test is present in echinoderm

Options

A. Asterias
B. Ophiura
C. Echinocardium
D. Antedon.

Answer

To answer the question "A test is present in echinoderm," we need to identify which echinoderm possesses a test, which is a tube-like structure. Let's analyze the options provided:

1. **Asterias (Starfish)**:
- Starfish do not have a test. They have a hard calcareous endoskeleton made up of ossicles, but not a tubular structure.
- **Conclusion**: This option is incorrect.

2. **Ophiura (Brittle Star)**:
- Brittle stars have long, flexible arms and a central disc but do not possess a tubular structure known as a test.
- **Conclusion**: This option is also incorrect.

3. **Echinocardium**:
- Echinocardium is a genus of sea urchins. They have a test, which is a hard, tubular structure that provides support and protection. The test is typically covered with small spines.
- **Conclusion**: This option is correct.

4. **Antidon (Cilily)**:
- Antidon, which refers to a type of ciliated echinoderm, does not have a test.
- **Conclusion**: This option is incorrect.

Based on the analysis, the correct answer is **Echinocardium**, as it is the only echinoderm listed that possesses a test.

### Summary of the Solution:
- **Step 1**: Evaluate the first option (Asterias) - no test present.
- **Step 2**: Evaluate the second option (Ophiura) - no test present.
- **Step 3**: Evaluate the third option (Echinocardium) - test is present.
- **Step 4**: Evaluate the fourth option (Antidon) - no test present.
- **Final Conclusion**: The correct answer is **Echinocardium**.