Answer: The correct answer for the blank is-
without a jaw.
Cyclostomata is a group of jaw-less fishes ( belonging to the super-class agnatha) under the phylum chordata.
It possesses the lampreys and hag-fishes, which are living jawless fishes. Both these groups possess mouths without jaws. Their epidermal structures are sharp, which act as as teeth, and branchial arches are located internally (unlike jawed fishes, which have externally positioned branchial arches).
Thus, without a jaw is the right answer.
