Question

Torsion occurs in the visceral mass of

• A. Gastropoda
• B. Pelecypoda
• C. Cephalopoda
• D. Monoplacophora

Answer 1

Answer: (A)

Gastropoda

Torsion is characteristic of Gastropoda. It is seen in all gastropods during larval development. Torsion occurs in the visceral mass. It is the phenomenon of rotation of the visceral mass, mantle, and shell at 180${}^0$. This results in the anterior position of mantle cavity and the anus above the head.

Thus, the correct answer is option A.