What is the location and function of nephridia?

Which is the locomotory organ of the sandworm $(Nereis)$?

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.

Assertion $A$: Metameric segmentation is observed in Annelids.
Reason $R$: The body of an Annelid is divided into two equal halves by a single axis.
Which option is correct for Assertion $A$ and Reason $R$?

What type of body cavity (coelom) is present in an earthworm?

The term $Annulus$ is derived from which language?