Which among the following is the only vertebrate osmoconformer?

Which of the following pairs of animals are jawless fishes?

Which of the following statements are correct for Cyclostomata?
$I$ - They have a sucking and circular mouth without jaws.
$II$ - Their body is devoid of scales and paired fins.
$III$ - Their cranium and vertebral column are cartilaginous.
$IV$ - They have a closed type of circulatory system.
$V$ - Cyclostomes live in freshwater,but migrate to the ocean for spawning.
$VI$ - They show direct development.

Which of the following pairs of animals represents 'jawless fishes'?

Match the name of the animal (Column-$I$) with one characteristic (Column-$II$), and the phylum/class (Column-$III$) to which it belongs.

Which of the following marine animals migrates to freshwater for spawning?