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

Which one of the following exhibits a concentric "tube within a tube" body plan?

Select the correct option:
$(1)$ Annelids are the first animals to possess a circulatory system.
$(2)$ The heart is called myogenic.

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?

The first true organ system grade of body organization is developed in:

Which of the following organisms does not show an open circulatory system?