Final answer:
Sharks belong to the class Chondrichthyes, which includes cartilaginous fishes with jaws, paired fins, and a skeleton made of cartilage. They possess several distinguishing features such as sharp teeth and a number of fins.
Step-by-step explanation:
Sharks are grouped in the class Pisces because this class is characterized by aquatic vertebrates that possess fins. In fact, sharks are not part of Pisces, but are a subset of fish known as the class Chondrichthyes, which is the class of cartilaginous fish.
They are distinguished from other fish by having a skeleton made of cartilage, rather than bone. Sharks also have multiple rows of sharp teeth and a number of fins that contribute to their classification. While some sharks do lay eggs (oviparous), this is not a defining characteristic of all shark species, as some are livebearers (viviparous).