By which of the following nephridia excretion is exonephric?

Options

A. Pharyngeal nephridia
B. Septat nephridia
C. Integumentary nephridia
D. Integumentary and pharyngeal nephridia

Answer

To determine which type of nephridia is associated with exonephric excretion, we can analyze the options provided:

1. **Pharyngeal Nephridia**:
- These nephridia open into the alimentary canal.
- They excrete waste products into the alimentary canal.
- This type of excretion is known as **ateronaphric** excretion.

2. **Septate Nephridia**:
- Similar to pharyngeal nephridia, septate nephridia also open into the alimentary canal.
- They excrete waste into the alimentary canal as well.
- Therefore, this is also classified as **ateronaphric** excretion.

3. **Integumentary Nephridia**:
- In contrast to the previous two, integumentary nephridia open to the exterior surface of the body.
- They excrete waste products directly to the outside environment.
- This type of excretion is referred to as **exonephric** excretion.

4. **Combination of Integumentary and Pharyngeal Nephridia**:
- Since pharyngeal nephridia are ateronaphric, this option cannot be exonephric.

Based on this analysis, the correct answer to the question is **Integumentary Nephridia**, as they are responsible for exonephric excretion.

### Summary of Steps:
1. Identify the function of pharyngeal nephridia and their type of excretion.
2. Identify the function of septate nephridia and their type of excretion.
3. Identify the function of integumentary nephridia and their type of excretion.
4. Analyze the combination option and determine its classification.
5. Conclude that integumentary nephridia are responsible for exonephric excretion.