A) Gastropoda
B) Pelecypoda
C) Cephalopoda
D) Amphineura
Correct Answer: A
Solution :
Torsion is an anatomical event, which takes place during the very early part of the life of snails and slugs of all kinds. In other words, torsion is a gastropod synapomorphy, which occurs in all gastropods during larval development. Torsion is the rotation of the visceral mass, mantle and shell 180° with respect to the head and foot of the gastropod. This brings the mantle cavity and anus to an anterior position above the head.
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