Sharks belong to a class of fish called Chondrichthyes, which have skeletons made of cartilage and not bone.
Sharks are typically slow growing, late maturing, long-lived and produce only a few young per year, which makes many species more vulnerable to overfishing than most bony fish.
Sharks are covered in tough scales called dermal denticles, making their skin extremely tough and abrasive. Sharks have between five and seven external gills.
Some sharks that live on the seabed, such as angel sharks and wobbegongs, have a flattened shape, like a ray. However, most sharks have a torpedo shaped body, large dorsal and pectoral fins to keep them stable and to help them steer, and a large tail or ‘caudal’ fin for propulsion.
Many sharks need to keep swimming in order to breathe, while others can pump water over their gills while they’re still or above the seabed.
Sharks have a continuous supply of teeth to replace damaged teeth. A shark can have up to 3,000 teeth in its mouth at one time and produce more than 30,000 teeth in its lifetime.
Sharks’ teeth vary according to their diet. White sharks have large serrated teeth for cutting big prey, while grey nurse sharks have long, needle-like teeth, used for gripping prey. Port Jackson sharks and many ray species have large plate-like teeth for crushing hard-shelled prey, like crabs and other invertebrates.