Question

Choose the correct stages in the development of Gastropods to indicate occurrence of torsion:

• A. A, B, C, D, E
• B. A, C, D, B, E
• C. B, A, C, D, E
• D. A, B, D, C, E

Hint:

Torsion happens in two $90^{\circ}$ steps. The $180^{\circ}$ total flip makes the gastropod look “twisted.”

Answer 1

The Correct Option is D

Step 1: Concept
Torsion is a $180^{\circ}$ counterclockwise twisting of the visceral mass in gastropod mollusks during development. Step 2--3: Analysis
Pre-torsional stage (A). First $90^{\circ}$ lateral counter-clockwise twist (B). Larva with ventral flexure (D). Mantle cavity and anus move to the right (C). Final $90^{\circ}$ torsion in the adult stage (E).

Step 4: Conclusion
The sequence is A $\to$ B $\to$ D $\to$ C $\to$ E.

Final Answer: (D)