Brown Hydra is

Options

A. Hydra vulgaris
B. Hydra viridis
C. Hydra fusca
D. Hydra gangeticus.

Answer

To determine which species of Hydra is referred to as the "brown hydra," we can analyze the options provided step by step.

### Step-by-Step Solution:

1. **Identify the Options**: The options given are:
- Hydra vulgaris
- Hydra viridis
- Hydra fusca
- Hydra gangeticus

2. **Evaluate Hydra vulgaris**:
- Hydra vulgaris is known as a freshwater polyp but is not recognized as the brown hydra.
- **Conclusion**: This option is incorrect.

3. **Evaluate Hydra viridis**:
- Hydra viridis is known for its green color, which is due to a symbiotic relationship with green algae (specifically, Chlorella).
- **Conclusion**: This option is also incorrect as it is known as the green hydra.

4. **Evaluate Hydra fusca**:
- Hydra fusca is specifically known as the brown hydra. Its brown coloration is due to the presence of certain pigments.
- **Conclusion**: This option is correct.

5. **Evaluate Hydra gangeticus**:
- Hydra gangeticus is referred to as the Indian hydra and is not known as the brown hydra.
- **Conclusion**: This option is incorrect.

### Final Answer:
The correct answer is **Hydra fusca**, which is known as the brown hydra.

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