Sharks are characterized by cartilaginous skeleton and they have 5 to 7 gill slits on the side of their head.And they have pectoral fins not fused to the head.
The earliest known shark dates back 420 million years ago.Since then,Sharks have diverse into 500 species.They can range in size from small, to a dwarf lantern shark the largest shark is a whale shark.
You will be able to find sharks all over the sea sharks are commonly found up to depth of 2,000 meters.They are generally not one for freshwater,but there has been a few known exceptions, the bull shark and River shark ,can survive and be found in freshwater and sea water.They breathe through 5 to 7 gill slits.
You will also find they have several replacement teeth. Well-knownSharks such as the great white shark, Tiger shark, blue shark, are all the apex predators.They are at the top of underwater food chain.