What is common between the trichocysts of $Paramecium$ and the nematocysts of $Hydra$?

In which of the following are cleidoic eggs found?

The circulatory system shown in the given figure is found in which of the following animals?

Identify the correct terms for the following analogy-based questions:
$(i)$ Aquatic Annelids : Parapodia :: Arthropods : ....
$(ii)$ Annelids : Nephridia :: Arthropods : ....

Some characteristics are given below:
$(1)$ Polymorphism $(2)$ Metagenesis $(3)$ Metamorphosis
$(4)$ Canal system $(5)$ Cnidoblast cells $(6)$ Blind sac body plan
Select the correct statement:

Which character is not the same in $Aves$ and $Mammals$?