Question

Difference between torsion & detorsion in gastropoda(4 points)​

Answer 1

Answer:

Torsion allows foot to be retracted after the head for better protection of head. Detorsion is reversal of torsion which takes place when during evolution shell is lost or a type of shell evolves that has openings on the opposite sides. In such situations twisting of visceral mass is not necessary.

Answer 2

Torsion permits the foot to be retracted after the head for improved head protection, but detorsion is a reversal of torsion that occurs when the shell is destroyed during evolution or a form of shell evolves with openings on opposing sides.

Torsion in gastropoda:

• Torsion is a gastropod synapomorphy that occurs during larval development in all gastropods.
• Torsion is the 180° rotation of the gastropod's visceral mass, mantle, and shell with regard to the head and foot.
• The mantle cavity and the anus move to an anterior position above the skull as a result of this rotation.
• Torsion is a unique method that gastropods use to turn their symmetric body plan into a radically asymmetric one.

Detorsion in gastropoda:

• Detorsion is the partial or complete reversion of torsion.
• This occurs when a shell is lost during evolution or when a shell with openings on both sides evolves.
• As a result, detorsion occurs during the larval stage, and the animal becomes bilaterally symmetrical once more.

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