Unio is

Options

A. Edible Oyster
B. Marine Shellfish
C. Fresh Water Mussel
D. Sea Mussel.

Answer

To answer the question "Unio is," we will analyze the options provided and determine the correct classification of Unio.

### Step-by-Step Solution:

1. **Identify the Options**: The options given are:
- Edible oyster
- Marine shellfish
- Freshwater mussel
- Sea mussel

2. **Understand the Genus Unio**: Unio is a genus that refers to a specific type of organism. It is important to note that it is classified under the phylum Mollusca.

3. **Characteristics of Unio**: Unio is known to be a medium-sized freshwater mussel. It has a bivalve structure, meaning it has two shells (valves) that are asymmetrical.

4. **Determine the Correct Option**:
- **Edible oyster**: This is incorrect as Unio is not an oyster.
- **Marine shellfish**: This is also incorrect because Unio is not a marine organism; it is freshwater.
- **Freshwater mussel**: This is correct as Unio is indeed a freshwater mussel.
- **Sea mussel**: This is incorrect since Unio is not found in marine environments.

5. **Conclusion**: Based on the analysis, the correct answer is that Unio is a **freshwater mussel**.

### Final Answer:
Unio is a **freshwater mussel**.

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