Lamprey is

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.

Ammocoete larva occurs in the life-history of

$A$ jawless fish,which lays eggs in fresh water and whose ammocoetes larvae after metamorphosis return to the ocean is

Ventral muscular heart,kidneys for excretion and osmoregulation,and paired appendages are found in all of the following $EXCEPT$:

Statement $- I :-$ All living members of class $Cyclostomata$ are ectoparasites on some fishes.
Statement $- II :-$ $Cyclostomata$ have a sucking and circular mouth without jaws.