Why are whale sharks called shark?

Despite being called a shark, whale sharks are actually a species of fish in the subclass Elasmobranchii. They belong to the family Rhincodontidae, which includes only one other species, the whale shark (Rhincodon typus). These species are more closely related to rays and skates than to sharks, as they have a cartilaginous skeleton, five to seven-gill slits on each side of their head, and a spiracle (a small opening behind each eye) that allows them to breathe air at the surface of the water.