Assertion :In gastropods, due to torsion mantle cavity is placed anteriorly behind and above the head.
Reason: During larval stage, visceral mass, shell and mantle cavity are twisted upto 180 counter clockwise with respect to the head and foot.

Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.

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Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.

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Assertion is correct but Reason is incorrect.

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Both Assertion and Reason are incorrect.

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Solution

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
Torsion is an anatomical event which takes place during the very early part of the life of snails and slugs of all kinds. Torsion 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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Assertion :In gastropods, due to torsion mantle cavity is placed anteriorly behind and above the head. Reason: During larval stage, visceral mass, shell and mantle cavity are twisted upto 180 counter clockwise with respect to the head and foot.

Assertion :In gastropods, due to torsion mantle cavity is placed anteriorly behind and above the head.
Reason: During larval stage, visceral mass, shell and mantle cavity are twisted upto 180 counter clockwise with respect to the head and foot.