What is haemocoel?

Meena and Hari observed an animal in their garden. Hari called it an insect while Meena said it was an earthworm. Choose the character from the following which confirms that it is an insect.

$(i)$ Draw a neat diagram of Hydra.
$(ii)$ Label mesoglea and gastrovascular cavity.
$(iii)$ Name the group of animals it belongs to.
$(iv)$ Name one species of this group that lives in colonies.

$(a)$ State two characteristic features of nematodes.
$(b)$ Identify the phylum with the help of the following features:
$(i)$ Spiny-skinned,radially symmetrical,and have tube feet.
$(ii)$ Triploblastic,worm-like,having a segmented body.

What is a notochord? What is its function?

Real organs are absent in