Assertion : Lateral line system is found in fishes and aquatic larval amphibians.
Reason : Lateral line system has receptor of sensory cells derived form ectoderm.

Options

A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that the lateral line system is found in fishes and aquatic larval amphibians.
- This is true because the lateral line system is indeed a sensory organ system that helps these aquatic animals detect water movements and pressure changes.

2. **Understanding the Reason**:
- The reason states that the lateral line system has receptors of sensory cells derived from ectoderm.
- This is also true, as the sensory cells of the lateral line system originate from the ectoderm layer during embryonic development.

3. **Evaluating the Relationship**:
- Now we need to determine if the reason correctly explains the assertion.
- While both the assertion and reason are true, the reason does not specifically explain why the lateral line system is found in these organisms. It merely states a fact about the origin of the sensory cells.

4. **Conclusion**:
- Since both the assertion and reason are true, but the reason does not provide a correct explanation for the assertion, the correct answer is that both are true but the reason is not the correct explanation of the assertion.

### Final Answer:
- The correct option is: **Both assertion and reason are true but reason is not the correct explanation of assertion.**