Bilateral symmetry, metameric segmentation coelom and open circulatory system are the characters of

Options

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

Answer

To solve the question regarding which group of organisms exhibits bilateral symmetry, metameric segmentation, a coelom, and an open circulatory system, we can analyze each option step by step.

### Step 1: Understand the Characteristics
- **Bilateral Symmetry**: This means the organism can be divided into two equal halves that are mirror images of each other.
- **Metameric Segmentation**: This refers to the body being divided into repeated segments.
- **Coelom**: This is a true body cavity that is completely lined by mesoderm.
- **Open Circulatory System**: In this system, blood flows freely through cavities (sinuses) instead of being confined to blood vessels.

### Step 2: Analyze Each Option
1. **Annelida**:
- Bilateral symmetry: Yes
- Metameric segmentation: Yes (e.g., earthworms have segments)
- Coelom: Yes (they are true coelomates)
- Open circulatory system: No (they have a closed circulatory system)
- **Conclusion**: Does not satisfy all characteristics.

2. **Mollusca**:
- Bilateral symmetry: Yes
- Metameric segmentation: No (they do not have true segmentation)
- Coelom: Yes (they are true coelomates)
- Open circulatory system: Yes (most have an open circulatory system)
- **Conclusion**: Does not satisfy all characteristics.

3. **Arthropoda**:
- Bilateral symmetry: Yes
- Metameric segmentation: Yes (e.g., cockroaches have segmented bodies)
- Coelom: Yes (they are true coelomates)
- Open circulatory system: Yes (they have an open circulatory system)
- **Conclusion**: Satisfies all characteristics.

4. **Echinodermata**:
- Bilateral symmetry: No (they exhibit radial symmetry in adults)
- Metameric segmentation: No (they do not have true segmentation)
- Coelom: Yes (they are true coelomates)
- Open circulatory system: Yes (they have an open circulatory system)
- **Conclusion**: Does not satisfy all characteristics.

### Final Answer
Based on the analysis, the only group that satisfies all four characteristics (bilateral symmetry, metameric segmentation, coelom, and open circulatory system) is **Arthropoda**.