$A$ definite number of body segments is found in

What does a sandworm (Nereis) possess for locomotion?

Which of the following animals possesses a closed circulatory system containing blood capillaries?

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.

Annelids have a central nerve cord that is

$A$: True coelom originated for the first time in phylum $Annelida$.
$R$: It allowed the animal to have an alimentary canal longer than the body and space for storing gametes.