All living members of the class Cyclostomata are:

The correct option is Ectoparasite.

Explanation:

Cyclostomes (class Cyclostomata) are a group of primitive, jawless vertebrates which includes lampreys and hagfishes.

All living members of the class Cyclostomata are ectoparasites on some fishes. They have an elongated body, lack jaws, and possess a sucking and circular mouth. Using this specialized mouth, they attach themselves to the body of host fishes to feed on their blood and tissue fluids, living as parasites on the outer surface of their hosts (ectoparasites).