The first segment of annelids is

Options

A. Prostomium
B. Peristomium
C. Prestomium
D. Poststomium

Answer

To solve the question "The first segment of annelids is," we will analyze the options provided and understand the anatomy of annelids.

### Step-by-Step Solution:

1. **Understand the Structure of Annelids**:
- Annelids are segmented worms, and their bodies are divided into different segments. Each segment has a specific name and function.

2. **Identify the Options**:
- The options given are:
1. Prostomium
2. Peristomium
3. Pre-stomium
4. Post-stomium

3. **Define Each Term**:
- **Prostomium**: This is the region located before the mouth. It is not considered a segment but rather an extension that hangs over the mouth.
- **Peristomium**: This is the first true segment of the annelid body, which surrounds the mouth.
- **Pre-stomium**: This term is not commonly used in annelid anatomy.
- **Post-stomium**: This term is also not recognized in the context of annelid segmentation.

4. **Determine the Correct Answer**:
- Since the peristomium is the first segment that directly follows the prostomium and surrounds the mouth, it is the correct answer.
- The prostomium, while important, is not counted as a segment in the segmented body plan of annelids.

5. **Conclusion**:
- The first segment of annelids is the **peristomium**.

### Final Answer:
The first segment of annelids is **peristomium**.