The lamprey $(Petromyzon)$ is included in the same taxonomic class as the

Skin without scales and presence of unicellular mucous glands are characteristics of which class of animals?

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

Hemicyclaspis belongs to the class

$A$ 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 of the following is a jawless class?