Photoreceptors (phaosomes) in earthworm occur in

Options

A. Epidermis of dorsal body wall and prostomium
B. Epidermis of ventral body wall
C. Both (1) and (2)
D. Epidermis ofprostomium only

Answer

To answer the question about the location of photoreceptors (phaosomes) in earthworms, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Earthworm Anatomy**:
- Earthworms have a segmented body structure. The first segment is called the prostonium, which is a cephalized part of the worm.

2. **Identifying Photoreceptors**:
- Earthworms do not possess eyes but have specialized light-sensitive cells known as photoreceptors or phosomes. These cells are crucial for light detection.

3. **Location of Photoreceptors**:
- According to the information, photoreceptors are distributed throughout the epidermis of the earthworm. However, they are more concentrated in specific areas.

4. **Concentration Areas**:
- The photoreceptors are primarily found in the epidermis of the dorsal body wall and the prostonium. The dorsal side refers to the back of the earthworm, while the prostonium is the first segment.

5. **Additional Details**:
- It is noted that while there are some photoreceptors on the ventral side, they are more abundant on the dorsal side and in the prostonium. Beyond the third segment, their numbers decrease significantly.

6. **Final Answer**:
- Based on the concentration and distribution of these photoreceptors, we conclude that the photoreceptors (phaosomes) in earthworms occur in the epidermis of the dorsal body wall and the prostonium.

### Final Answer:
Photoreceptors (phaosomes) in earthworms occur in the epidermis of the dorsal body wall and prostonium.

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