In which group of molluscs is torsion a very important event in the life history?

The mantle cavity is located between:

$A$ shell of calcium carbonate,a mantle,and a radula are characteristic features of which of the following?

Which invertebrate phylum exhibits unisexual or hermaphrodite conditions,external or internal fertilization,and direct or indirect development?

Assertion : Torsion can be seen in ctenidium.
Reason : Ctenidium acts as the respiratory organ.

Which one of the following is a distinctive character of class $Bivalvia$ of the phylum $Mollusca$?