Which class of Mollusca undergoes 'torsion' during larval development, rotating the visceral mass 180 degrees?
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Correct answer: Gastropoda
Torsion is a developmental process unique to gastropod larvae, in which the entire visceral mass and mantle cavity rotate 180 degrees relative to the head and foot. This brings the mantle cavity, gills, and anus to an anterior position above the head, providing protection for these organs when the animal retracts into its shell.
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