A) both (A) and (R) are true and (R)explains
B) both (A) and (R) are true but (R) cannot explain
C) only (A) is correct but (R) is wrong
D) both (A) and (R) are wrong
Correct Answer: A
Solution :
Gastropods are generally believed to have descended from an unsegmented and bilaterally symmetrical ancestor with a low conical shell, a straight alimentary canal ending in a posterior anus and mantle cavity. In many gastropods the anus and mantle cavity are placed anteriorly above the head. Torsion or twisting is a process, during larval development of gastropods, which rotates the viscero-pallium anti-clockwise through \[180{}^\circ \] from its initial position, so that mantle cavity, with its pallial complex, is brought in front of the body, in adult.
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