Question

Statement (S): In many gastropods, the anus and mantle cavity are placed anteriorly above the head.

Reason (R): During embryonic development, in many gastropods, one side of the visceral mass grows faster than the other side. The uneven growth rotates the visceral organs upto ${180}^0$ in many gastropods.

• A. Both S and R are true and R explains S
• B. Both S and R are true but R cannot explain S
• C. Only S is correct R is wrong
• D. Both S and R are wrong

Answer 1

The correct option is A Both S and R are true and R explains S

A. Both S and R are true and R explains S

Reason: In gastropoda, shell is made up of one piece. The early embryo is symmetrical but during development the body twists showing torsion so that the body becomes asymmetrical. During development in most gastropods, because of torsion, the animal's anus and mantle cavity both positioned above the head.