Pharyngeal nephridia of Earthworm $Pheretima$ occur in segments

The copulation period of an Earthworm is:

The first segment of the earthworm is called:

For earthworms,identify the $(i)$ Class,$(ii)$ Genus,$(iii)$ Order,and $(iv)$ Family.

Study the following in $Pheretima$.
$I.$ Dorso-intestinal blood vessels
$II.$ External intestinal plexus
$III.$ Internal intestinal plexus
$IV.$ Ventro-intestinal blood vessel
Arrange the blood vessels in the correct sequence of blood flow from the ventral blood vessel to the dorsal blood vessel.
The correct sequence is:

How many pairs of hearts are found in earthworms (in $pairs$)?