The youngest and the oldest segment in earthworm respectively 

Options

A. Peristonium and pygidium
B. Pygidium and peristomium
C. Preanal segment and peristomium
D. Peristomium and preanal segment

Answer

To determine the youngest and oldest segments in an earthworm, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Earthworm Segmentation**:
- Earthworms are segmented animals, meaning their bodies are divided into multiple segments called metameres. An earthworm typically has about 100 to 200 segments.

2. **Identifying the Youngest Segment**:
- The youngest segment in an earthworm is known as the **prenal segment**. This segment is located at the posterior end of the earthworm.

3. **Identifying the Oldest Segment**:
- The oldest segment in an earthworm is referred to as the **peristome**. This segment is also known as the buccal segment and is located at the anterior end of the earthworm, containing the mouth.

4. **Understanding Segment Functions**:
- The peristome (oldest segment) plays a crucial role as it is involved in feeding, while the prenal segment (youngest segment) is involved in the growth of the earthworm.

5. **Conclusion**:
- Therefore, the youngest segment of the earthworm is the **prenal segment**, and the oldest segment is the **peristome**.

### Final Answer:
- The youngest segment in an earthworm is the **prenal segment**, and the oldest segment is the **peristome**.

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