In earthworm, there is a ring of S-shaped setae, embedded in the epidermal pit at the middle of each segment except

Options

A. First
B. Last
C. Clitellar
D. First, last, and clitellar segments

Answer

To solve the question regarding the absence of S-shaped setae in earthworms, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Structure**:
- Earthworms have a body divided into segments, typically ranging from 100 to 120 segments. Each segment has a ring of S-shaped setae embedded in the epidermal pit.

2. **Function of S-shaped Setae**:
- These setae are lateral appendages that assist in locomotion, allowing the earthworm to move through soil and other substrates.

3. **Identifying Segments**:
- The segments of the earthworm are numbered from the anterior (front) to the posterior (back). The first segment is known as the peristomium.

4. **Segments Lacking S-shaped Setae**:
- The S-shaped setae are absent in the following segments:
- **Peristomium (1st segment)**: This is the first segment located at the anterior end of the earthworm.
- **Clitellar segment (14th to 16th segments)**: This segment contains glandular tissue important for reproduction.
- **Last segment**: The terminal segment of the earthworm also lacks setae.

5. **Conclusion**:
- Therefore, the segments where S-shaped setae are absent include the first segment (peristomium), the last segment, and the clitellar segment.

### Final Answer:
The S-shaped setae are absent in the first segment (peristomium), the last segment, and the clitellar segment.