Which of the following is $NOT$ a characteristic of $Cyclostomata$?

$A$ 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?

Which animals are marine but migrate to freshwater for spawning?

Which of the following statements is not true for $Agnatha$ members?

Which animals live in the sea but migrate to freshwater for breeding?

Petromyzon belongs to which of the following groups?