Which of these animals belongs in class Chondrichthyes?

The story behind the answer

Great white shark belongs to class Chondrichthyes—cartilaginous fishes with skeletons made of cartilage instead of bone. This group includes sharks, rays, and skates; they have placoid (tooth-like) scales, multiple gill slits, and an oil-rich liver for buoyancy rather than a swim bladder.

By contrast, catfish are bony fish (Osteichthyes), killer whales are mammals, and octopuses are mollusks (cephalopods). Memory tip: “Chondr-” means cartilage and “-ichthyes” means fish—cartilage-fish = sharks and rays.