A: Echinoderms are the only radially symmetrical animals with true coelom.
R: Echinoderms have secondarily adapted to radial symmetry.

Options

A. If both assertion & reason are true and the reason is the correct explanation of the assertion, then mark (1).
B. If both assertion & Reason are true but the reason is not the correct explanation of the assertion, them mark (2).
C. If assertion is true statement but reason is false, them mark (3).
D. If both assertion and reason are false statements, them mark (4).

Explanation

To solve the assertion and reason statement question regarding echinoderms, we can break it down into a step-by-step analysis.

### Step 1: Understand the Assertion
The assertion states that "Echinoderms are the only radially symmetrical animals with true coelom."
- **True Coelom**: Echinoderms indeed possess a true coelom, which is a body cavity completely lined by mesoderm.
- **Radial Symmetry**: However, it is important to note that radial symmetry is primarily observed in adult echinoderms. The larval stage of echinoderms exhibits bilateral symmetry.

### Step 2: Evaluate the Assertion
Given that only adult echinoderms are radially symmetrical and that their larvae are bilaterally symmetrical, the assertion is misleading. Therefore, the assertion is **false**.

### Step 3: Understand the Reason
The reason states that "Echinoderms have secondarily adapted to radial symmetry."
- **Secondary Adaptation**: This implies that echinoderms evolved from a bilaterally symmetrical ancestor and later adapted to radial symmetry in their adult form.

### Step 4: Evaluate the Reason
While it is true that echinoderms exhibit radial symmetry in their adult form, stating that they have "secondarily adapted" to this form is not entirely accurate. The evolution of echinoderms is complex, and while they do exhibit radial symmetry as adults, it is not correct to say they adapted to it in a straightforward manner. Thus, the reason is also **false**.

### Step 5: Conclusion
Since both the assertion and the reason are false, the correct answer to the question is that both statements are incorrect.

### Final Answer
Both the assertion (A) and the reason (R) are false.

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