Sharks can detect incredibly small electrical fields. The head of a shark has a large number of small pores that lead to an elaborate system of sensory tubes. These tubes, called ampullae of Lorenzini, are sensitive to electrical fields. Sharks can locate and capture a fish by sensing the small electrical field produced by its gills. Sharks also seem to use their electrical sense for navigation and migration.
Sharks belong to a group of fishes known as elasmobranchs.
Rays and skates also belong to this group. Scientists do not know exactly how many kinds of sharks there are. They occasionally identify new species. But sometimes they find that two sharks that had been considered different species are actually the same. This section describes some of the best-known sharks.