Given below are two statements. One is labelled as Assertion $(A)$ and the other is labelled as its Reason $(R)$.
Assertion $(A) :$ In $Nereis$, longitudinal and circular muscles help in locomotion.
Reason $(R) :$ $Nereis$ is an aquatic annelid which is monoecious and possesses lateral appendages called parapodia, which help in swimming.

• A
  $(A)$ is true but $(R)$ is false
• B
  $(A)$ is false, $(R)$ is true
• C
  Both $(A)$ and $(R)$ are true and $(R)$ is not the correct explanation of $(A)$
• D
  Both $(A)$ and $(R)$ are true and $(R)$ is the correct explanation of $(A)$