What is a Shark?

Sharks are a type of fish, but they are different from other fishes in several ways:

Sharks share most of their characteristics with other fishes. However, they differentiate by having a cartilage skeleton instead of bone; by having visible gill slits and not an operculum; by having dermal denticles in their skin and not scales; by having thick and rigid fins; and by not having osseous spines.