Shark , any of numerous species of cartilaginous fishes that make up the order Selachii (class Chondrichthyes). Most species have a tough skin that is dull gray in color and roughened by toothlike scales. The mouth contains sharp triangular teeth. Sharks lack a swim bladder and must swim to keep from sinking. Sharks Facts and Information. Facts about species, anatomy, distribution, reproduction, conservation and relation with humans. There are more than 500 species of sharks swimming in the world’s ocean. Yet when most people think of these cartilaginous fish, a single image comes to mind: a large, sharp-toothed and scary beast. That generalization does sharks a huge disservice, as they have far more variety than that. They range in size from the length of a human hand to more than 39 feet (12 meters) long; half of all shark species are less than one meter (or about 3 feet) long. They come in a variety of colors ... Sharks are a group of elasmobranch cartilaginous fishes characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the division Selachii[1] and are the sister group to the Batomorphi (rays and skates). Some sources extend the term "shark" as an informal category including extinct members of Chondrichthyes (cartilaginous fish) with a shark-like morphology, such as ...
