Which one of the following statements about certain given animals is correct?

Options

A. Molluscs are acoelomates .
B. Insects are pseudocoelomates .
C. Flatworms ( Platyhelminthes ).
D. Roundworms (Aschelminthes ) are pseudocoelomates.

Answer

To solve the question regarding which statement about certain animals is correct, we will analyze each statement provided and determine their validity step by step.

### Step-by-Step Solution:

1. **Understanding Mollusks**:
- Mollusks are known to have a true body cavity, which is a coelom.
- Their body cavity is filled with a fluid known as hemolymph, which circulates and encloses most internal organs.
- **Conclusion**: The statement that mollusks are coelomates is **correct**.

2. **Analyzing Insects**:
- Insects are also classified as coelomates, not pseudocoelomates.
- They have a true body cavity filled with hemolymph, similar to mollusks.
- **Conclusion**: The statement that insects are pseudocoelomates is **incorrect**.

3. **Examining Flatworms**:
- Flatworms (Platyhelminthes) are known to be acoelomates, meaning they lack a true body cavity.
- They do not have a coelom or pseudocoelom.
- **Conclusion**: The statement regarding flatworms is **incorrect**.

4. **Reviewing Roundworms**:
- Roundworms (Nematodes) belong to the group Aschelminthes and are classified as pseudocoelomates.
- They possess a body cavity that is not completely lined by mesodermal cells, hence the term "pseudocoelomate" (false body cavity).
- **Conclusion**: The statement that roundworms are pseudocoelomates is **correct**.

5. **Final Conclusion**:
- Based on the analysis, the only correct statement among the options given is that roundworms belong to Aschelminthes and are pseudocoelomates.

### Answer:
The correct statement is: **Roundworms belong to Aschelminthes and are pseudocoelomates.**

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