In which of the following phyla did a true coelom first evolve?

Closed circulatory system is found in?

The first phylum of animals to exhibit a true coelom is:

Leech is:

Metamerism or metameric segmentation is a characteristic feature of

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.