Explain torsion in gastropods with the help of suitable diagrams.

Question

24 Jan 2022

Answer :

Word Count : 317

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 rotation brings the mantle cavity and the anus to an anterior position above the head.

There are two different developmental stages which cause torsion. The first stage is caused by the development of the asymmetrical velar/foot muscle which has one end attached to the left side of the shell and the other end has fibres attached to the left ___ _____ ________ __________ ________ __________ _______.
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