Doris is

Options

A. Fresh water mollusc
B. marine mollusc
C. Terrestrial mollusc
D. Connecting link between molluscs and annelids.

Answer

To solve the question "Doris is," we need to analyze the options provided: freshwater mollusk, marine mollusk, terrestrial mollusk, and connecting link between mollusks and annelids.

### Step-by-Step Solution:

1. **Identify Doris**:
- Doris is a genus that is commonly referred to as "sea slugs."

2. **Determine the Habitat**:
- Sea slugs, including those in the Doris genus, are primarily found in marine environments, meaning they live in the ocean.

3. **Evaluate the Options**:
- **Freshwater Mollusk**: This would refer to mollusks that live in freshwater environments, such as rivers and lakes. Doris does not belong to this category.
- **Marine Mollusk**: Since Doris is a sea slug, it is classified as a marine mollusk. This option fits perfectly.
- **Terrestrial Mollusk**: These are land-dwelling mollusks. Doris does not fit this category as it is not found on land.
- **Connecting Link between Mollusks and Annelids**: The organism Neopilina serves as a connecting link between mollusks and annelids, not Doris.

4. **Conclusion**:
- Based on the information, the correct classification for Doris is that it is a **marine mollusk**.

### Final Answer:
Doris is a marine mollusk.