what is significance of torsion?
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Torsion is the rotation of the visceral mass, mantle and shell 180˚ with respect to the head and foot of the gastropod. ... Torsionhas played the most important role in the evolutionary history of Gastropoda.
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Torsion is the result of a larval mutation but they do not agree on the advantage of such mutation restricted only to the larva or extends to the adult.
Due to torsion the mantle cavity becomes anterior and the sensitive parts of the anterior end including the head and also the foot of the larva could be withdrawn into the mantle cavity at the approach of danger. Garstang (1928) holds that torsion represents a larval mutation, which is of advantage to the larva and not the adult, a concept shared by Yonge (1947).
By rotation the anteriorly placed mantle cavity provides a refuge for the delicate head and velar lobes of the larva, and it is not directly advantageous to the adult.
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