Which of the following are animals belonging to the class $Cyclostomata$?

Which of the following is not a class of $Tetrapoda$?

Which of the following is an exclusively marine animal?

$A$ group of researchers procured some fish-like animals and upon investigation the following characters were observed: $A$. Endoskeleton was made of cartilage. $B$. Ectoparasitic; as they were found attached on fish skin with their circular sucking mouth. $C$. Paired fins and scales were absent, but $7$ pairs of gill slits were present. Which of the following species of animals did they consider to fit best with these characters?

Ammocoete larva occurs in the life-history of

The $Petromyzon$ belongs to: