What class of cartilaginous fishes includes sharks, rays, skates, and chimaeras?

The class of cartilaginous fishes that includes sharks, rays, skates, and chimaeras is Chondrichthyes.

Chondrichthyes is a class of jawed vertebrates whose internal skeletons are made primarily of cartilage rather than true bone. The group includes the shark-and-ray lineage, Elasmobranchii, and the chimaera lineage, Holocephali. Sharks, rays, and skates are therefore relatives within the same broad class, even though their body shapes and lifestyles can look dramatically different.

Members of Chondrichthyes also share features such as paired fins, internal fertilization, and tooth-like skin structures called dermal denticles or placoid scales. These denticles can make shark skin feel like sandpaper and help reduce drag through the water. Reproduction varies: some species lay egg cases, while others give birth to live young.

A common mistake is treating Chondrichthyes as a synonym for sharks alone. Sharks are one part of the class, and rays and skates belong to the elasmobranch group alongside them. Chimaeras, sometimes called ghost sharks, are also chondrichthyans but sit in the separate subclass Holocephali. The contrasting class Osteichthyes contains the bony fishes.