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

What is the location and function of nephridia?

Read the following four statements $(A-D)$:
$(A)$ Annelids possess only longitudinal muscles which help in locomotion.
$(B)$ Nephridia do not help in excretion and osmoregulation.
$(C)$ Closed type circulatory system is present in most of annelids.
$(D)$ Members of phylum Annelida are triploblastic,metamerically segmented,and acoelomate.
How many of the above statements are incorrect?

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 $R$?

True coelom or body cavity occurs in

$A$ suctorial mouth is present in