Clitellum occurs over 11 and 12 segment in

Options

A. Pheretima
B. Tubifex
C. Lumbricus
D. Megascolex

Answer

To determine where the clitellum occurs in the given options, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Clitellum**:
- The clitellum is a thick, glandular band found on the body of certain annelids, specifically earthworms. It is crucial for reproduction as it secretes a mucous ring that forms a cocoon for fertilized eggs.

2. **Identify the Options**:
- The options provided are:
1. Ferritima
2. Tubifex
3. Lumbricus
4. Megascollex

3. **Know the Characteristics of Each Option**:
- **Ferritima**: An earthworm, typically has the clitellum in segments 14-16.
- **Tubifex**: Known as the sewage worm, has the clitellum in segments 11-12.
- **Lumbricus**: Another type of earthworm, with the clitellum in segments 14-16.
- **Megascollex**: A large earthworm, also has the clitellum in segments 14-16.

4. **Analyze the Information**:
- From the knowledge of these worms, we can see that Tubifex is unique among the options as it has the clitellum located specifically in segments 11 and 12.

5. **Conclusion**:
- Therefore, the correct answer to the question is **Tubifex**, as it is the only worm listed that has the clitellum occurring in segments 11 and 12.

### Final Answer:
The clitellum occurs over segments 11 and 12 in **Tubifex**.