Which class of animals possesses a closed circulatory system?

The distinctive feature of $Phylum$ $Annelida$ is:

What is the location and function of parapodia or chitinous setae?

Animals of this phylum excrete through nephridia.

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.