Statement (s). In many gastropods, the anus and mantle cavity are placed anteriorly above the head.
Reason (R ). During embryonic development, in many gastropods one side of the visceral mass grows faster rotates the viscetal organs upto `180^(@)`

Options

A. Both S and R are true and R explains S
B. Both S and R are true but R cannot explain S
C. Only S is correct Ris wrong
D. Both S and R are wrong

Answer

To analyze the given statement and reason regarding gastropods, we can break it down into a step-by-step solution:

### Step 1: Understand the Statement
The statement claims that in many gastropods, the anus and mantle cavity are positioned anteriorly above the head.

**Hint:** Consider the anatomy of gastropods and their body structure.

### Step 2: Verify the Statement
This statement is indeed true. In many gastropods, due to a process called torsion, the anus and mantle cavity do end up positioned above the head.

**Hint:** Recall the unique anatomical features of gastropods compared to other mollusks.

### Step 3: Understand the Reason
The reason provided states that during embryonic development, one side of the visceral mass in many gastropods grows faster, causing a rotation of the visceral organs by 180 degrees.

**Hint:** Think about the developmental processes in gastropods and how they differ from other mollusks.

### Step 4: Verify the Reason
This reason is also true. The phenomenon described is known as torsion, which is a characteristic feature of gastropods. This process results in the rearrangement of the internal organs, leading to the positioning of the anus and mantle cavity above the head.

**Hint:** Consider how torsion affects the orientation of the body parts in gastropods.

### Step 5: Determine the Relationship
Now, we need to establish whether the reason correctly explains the statement. Since the process of torsion is responsible for the positioning of the anus and mantle cavity in gastropods, the reason does indeed explain the statement.

**Hint:** Reflect on how developmental processes can lead to anatomical changes.

### Conclusion
Both the statement and the reason are true, and the reason correctly explains the statement. Therefore, the appropriate conclusion is that both the statement and reason are correct, and the reason is the correct explanation for the statement.

**Final Answer:** Both the statement and reason are true, and the reason explains the statement.