Respuesta :
Answer: The correct answer for the blank is-
Cartilaginous fishes.
Chondrichthyes is a class of cartilagenous fishes. This means that they have their entire skeleton system made up of cartilages ( unlike bony fishes whose skeleton is made up of bones) as they are devoid of true bones.
This class of fishes have exposed gills that is there is no preotection of gill slits ( unlike bony fishes, which have protective membrane over gill slits). They bear toothlike placoid scales.