Which animal in the phylum $Annelida$ exhibits separate sexes (dioecious)?

Match the following columns:

Column-$I$ (Animal)	Column-$II$ (Genus)
$P$. Sandworm	$I$. Nereis
$Q$. Earthworm	$II$. Hirudinaria
$R$. Leech	$III$. Pheretima

What does a sandworm (Nereis) possess for locomotion?

Given below are two statements. One is labelled as Assertion $(A)$ and 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.

$A$: Annelids exhibit metameric segmentation.
$R$: The body of an annelid is divided into two equal halves by a single plane.

$P$ (Assertion): The first circulatory system is observed in the phylum Annelida.
$Q$ (Reason): The first true coelom is observed in the phylum Annelida.