Septal nephridia of earth worm are:-

Options

A. Responsible for excretion
B. Present in all body segments
C. To keep the surface moist
D. Present in 4,5,6 segments

Answer

**Step-by-Step Solution:**

1. **Understanding Septal Nephridia**: Septal nephridia are excretory structures found in earthworms. They play a role in the excretion of waste products from the body.

2. **Location**: Septal nephridia are present in specific segments of the earthworm. They are located in the intersegmental septa, primarily situated in segments 4, 5, and 6.

3. **Structure**: Each septal nephridium consists of a terminal duct that is short. There are multiple such ducts that open into a pair of septal excretory ducts.

4. **Function**: The septal excretory ducts then lead to the supra-intestinal excretory ducts. These ducts ultimately open into the lumen of the intestine, facilitating the excretion process.

5. **Clarification of Misconceptions**: It is important to note that septal nephridia are not present in all body segments of the earthworm. They are specifically absent in segments beyond the 15th segment.

6. **Conclusion**: Based on the information, the correct understanding is that septal nephridia are primarily responsible for excretion, located in segments 4, 5, and 6, and are not present in all segments.

**Final Answer**: Septal nephridia of earthworms are located in segments 4, 5, and 6, and they are responsible for excretion.

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