Which annelid is dioecious?

Match the following columns:

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

In which phylum of animals is the digestive tract either straight or coiled?

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.

Which one of the following exhibits a concentric '$tube\; within\; tube$' body plan?

$A$: 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.