Protonephridia of flatworms are primarily concerned with

Options

A. ionic and fluid volume regulation
B. excretion of ammonium ions with their excretory organs
C. egestion of undigested waste
D. expulsion of gametes during copulation

Answer

To solve the question regarding the primary function of protonephridia in flatworms, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Protonephridia**: Protonephridia are specialized excretory structures found in certain invertebrates, including flatworms. They are a type of nephridia, which are organs involved in excretion and osmoregulation.

2. **Function of Protonephridia**: The primary function of protonephridia is to regulate the ionic balance and fluid volume within the organism. This is crucial for maintaining homeostasis in the flatworm's body.

3. **Identifying Key Terms**: The key terms here are "ionic regulation" and "fluid volume regulation." These terms indicate that protonephridia play a significant role in managing the internal environment of flatworms, particularly in terms of salt and water balance.

4. **Evaluating Options**:
- Option A: "Ionic and fluid volume regulation" - This aligns with the known function of protonephridia.
- Option B: "Excretion of ammonium ions within excretory organs" - While protonephridia do help in excretion, this option is too specific and not the primary function.
- Option C: "Addition of undigested waste" - This is incorrect as protonephridia do not add waste but rather help in its removal.
- Option D: "Expulsion of gametes during copulation" - This is unrelated to the function of protonephridia.

5. **Conclusion**: Based on the analysis, the correct answer is Option A, which states that protonephridia of flatworms are primarily concerned with ionic and fluid volume regulation.

### Final Answer:
**The protonephridia of flatworms are primarily concerned with ionic and fluid volume regulation.**

---