In which phylum of animals do nephridia act as osmoregulatory organs?

Which of the following species are earthworms?
$I-$ Nereis,$II-$ Pheretima
$III-$ Hirudinaria,$IV-$ Lumbricus
$V-$ Periplaneta

Members of which phylum exhibit adaptations to widely varied environmental conditions?

Which animal in the phylum $Annelida$ exhibits separate sexes (dioecious)?

The first animal phylum to possess a circulatory system is: ........

Which organism belongs to the class Oligochaeta?