What is the exoskeleton of fish made of?

Water circulatory system is found in:
$I.$ Sponge
$II.$ Hydra
$III.$ Annelida
$IV.$ Starfish
$V.$ Arthropoda
Choose the correct option.

In which of the following are cleidoic eggs found?

Select the correct option for the following statements:
$(i)$ Platyhelminthes are pseudocoelomate / acoelomate.
$(ii)$ Cnidarians are radially symmetrical / asymmetrical.

Which of the following is considered a living fossil?

The point by which $Annelida$ advanced over $Nematoda$ is