One of the following is not an Annelida

Options

A. Nereis
B. Earthworm
C. Leech
D. Sea urchins

Explanation

To determine which of the given options is not an Annelida, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Phylum Annelida**:
- Annelids are segmented worms that belong to the phylum Annelida. They are characterized by their segmented bodies, bilateral symmetry, and a coelom (body cavity).

2. **Identify the Options**:
- The options provided include Nereis, Earthworm, Leeches, and Sea Urchin.

3. **Analyze Each Option**:
- **Nereis**: This is a genus of polychaete worms, which are indeed annelids.
- **Earthworm**: Commonly known as Lumbricus terrestris, earthworms are classic examples of annelids.
- **Leeches**: These are also annelids, belonging to the subclass Hirudinea.
- **Sea Urchin**: This is a marine animal that belongs to the phylum Echinodermata, not Annelida.

4. **Conclusion**:
- Since Nereis, Earthworm, and Leeches are all members of the phylum Annelida, the only option that is not an annelid is the Sea Urchin.

5. **Final Answer**:
- The correct answer is **Sea Urchin** (option 4), as it belongs to the phylum Echinodermata.