The larva of $Petromyzon$ is known as

Select the correct statement.

Identify the correct option for $Cyclostomata$ $:-$

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.

Petromyzon belongs to which of the following groups?

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