Sharks and their close cousins, the rays, evolved 400 million years ago and today there are about 510 species of shark and about 650 ray species in existence.
But we still know precious little about these enigmatic and often elusive fish.
Explore the incredible diversity of the sharks and rays, some of which you probably never knew existed, in this selection of wonderful images.
Scalloped hammerhead sharks
Scalloped hammerhead sharks (Sphyrna lewini) often swim alone, but large groups of the distinctively-shaped fish have been observed gathering at underwater mountains (seamounts) where they perform courtship “dances” with females taking up position in the centre of the circle.
Mobula rays, such as the individual photographed above in Mexico, are known for their stunning acrobatic feat of leaping out of the water, sometimes nearly 9ft (3m) into the air, making a loud splash as they flop back down.
The amazing spectacle happens when huge numbers of the rays (Mobula munkiana) gather to look for mates. However, no one is exactly sure of the reason behind their impressive leaps.
Port Jackson shark
Pre-historic in appearance, the bizarre Port Jackson shark (Heterodontus portjacksoni) is found around the southern, eastern and western coasts of Australia. Its teeth are small and pointy at the front and flat and wide at the back to crack and grind the shells of prey. Females produce spiral-shaped, brown eggs cases which are around 15cm long.
Great white shark
The most iconic of sharks, the great white (Carcharadon carcharias) is an inimitable predator but it has a less well-known social side as well. Groups of sharks gather and use body language to communicate with each other, sorting out disputes over kills and dominance.
But when they do hunt for prey, it is with impressive speed – in excess of 20mph (32kph) – and sometimes breach out of the water to snatch a seal. The element of surprise is an important part of these sharks' strategy, swimming up from below to surprise their prey. They are possibly one of the most feared sharks but attacks on humans are very few.
The mysterious frilled shark (Chlamydoselachus anguineus) inhabits the ocean’s abyss, and gets its name from its frilly-looking gills. The bizarre creature has a serpent-like body shape but only grows to about 6ft (2m) in length.
Oceanic whitetip sharks
Oceanic whitetip sharks (Carcharhinus longimanus) are distinguished by their very long and wide pectoral (breast) fins. These predators have extremely powerful jaws to grip their prey, and serrated teeth in its upper jaw to cut into flesh. Growing up to about 13ft (4m) in length, oceanic whitetip sharks are found in tropical and subtropical waters around the world, and can potentially be dangerous to humans.
Tasselled wobbegong shark
The curious-looking tasselled wobbegong shark (Eurcrossorhinus dasypogon) is found around northern Australia, Indonesia and Papua New Guinea. Its unusual markings allow it to camouflage itself and quickly grab unsuspecting prey. Its frilly “beard” may act as bait, as it resembles tasty small sea creatures, luring the shark's victims to its mouth.
Bigeye thresher shark
Bigeye thresher sharks (Alopias superciliosus) are believed to be harmless to humans. The distinctive-looking fish’s huge eyes are positioned high in its head and may be adapted to help it find prey silhouetted near the water’s surface.
Swell sharks get their name from their ability, when threatened, to swallow large amount of water or air causing them to swell to twice their normal size, putting predators off tackling them. These extraordinary sharks are also biofluorescent – they absorb light from the moon and emit it as a different colour. To a member of the same species, swell sharks (Cephaloscyllium ventriosum) appear bright green, and this may help potential mates find each other.
Ragged-tooth sharks (Carcharias taurus) are also known as grey nurse sharks or sand tiger sharks. They can reach over 10ft (3m) in length and their ragged-looking teeth, made up of larger teeth separated by smaller ones, give them a ferocious look. To stay buoyant, they gulp air from the surface and hold it in their stomachs. The sharks have been known to attack humans, but usually only when provoked.
'Shark' is a new three-part BBC/Discovery coproduction series that begins airing in the UK on BBC One on Thursday 7 May at 20:55 BST. It will be broadcast in other countries at a later date.
Discover more fun facts about the sharks and rays featuring in the 'Shark' series here.
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