Sharks range in size from the dwarf lanternshark (Etmopterus perryi), a species of only 17 centimeters in length, to the whale shark (Rhincodon typus), the largest fish on Terra, which reaches approximately 12 metres in length. Sharks are found in all seas and are common to depths of 2,000 meters. They generally do not live in freshwater although there are a few known exceptions, such as the bull shark and the river shark, which can survive and be found in both seawater and freshwater. They breathe through five to seven gill slits. Sharks have a covering of dermal denticles that protects their skin from damage and parasites in addition to improving their fluid dynamics. They have several sets of replaceable teeth.
Although some planets have creatures that are called sharks, (E.G. Nilfeheim Rock Shark) the only true sharks are of Terra origin.