Shark

Shark, any of the several predatory cartilaginous fish species that make up the order Selachii (class Chondrichthyes). Sharks, along with rays and skates, make up the Chondrichthyes subclass Elasmobranchii. Sharks, on the other hand, are distinguished from other elasmobranchs by their fusiform body shape and the placement of their gill clefts on each side of the skull. Sharks have thick skin that is drab grey in color and roughened by toothlike scales, though there are exceptions.A muscular, asymmetrical, upturned tail; pointed fins; and a pointed snout extending forward and over a crescentic mouth equipped with sharp triangular teeth are all common features. Sharks do not have a swim bladder, so they must swim constantly to avoid sinking to the bottom. According to various authorities, sharks are classified into 14–30 families, with over 400 species in existence. Humans are at risk from a number of larger animals. Sharks are fished commercially in large numbers. Overfishing in the late twentieth and early twenty-first centuries, on the other hand, drastically diminished the populations of some shark species.