Sharks have a never-ending supply of teeth. They regenerate replacement dentition on an inexhaustible toothy conveyor belt... which explains why you see so few shark dentists.
But sharks are not all about teeth, despite the bad press. Filter feeders like the megamouth shark, are mostly big (but harmless) mouths; the winghead shark has a head half the length of its body, and; the thresher sharks have a huge tail (ideal for stunning fish before eating them) that can be the same length as its body.
In many shark species the females have much thicker skin (I know, I know...). It can be twice the thickness of the males' skin and is thought to be an adaptation to endure ferocious bites from the males during sex.
That's not the only remarkable thing about shark skin, which is composed of tiny teeth like scales called 'denticles' which make it rough if you stroke it the wrong way. So rough, in fact, that it used to be used as sandpaper. The advantage is that in the other direction it makes the shark sleek and hydrodynamic. Shark skin leather (called Shagreen) has also been used for practical and ornamental purposes – including on the handles of ninja swords!
The world's biggest shark is the whale shark, a peaceful plankton-munching giant that can be 13.5 metres long. But it was dwarfed by a prehistoric giant shark, Megalodon, which was a pumped up ancestor of today's great white. It had six inch teeth and was much, much bigger, easily overshooting a double-decker bus in length, and possibly about the same size as today's Sperm whales. Think yourselves lucky they are (probably) no longer around.
The world's smallest shark is probably the dwarf lanternshark, which, like other lanternsharks, glows in the dark.
Sharks use electrical senses to find prey, and the oddly-shaped heads of the hammerhead family are used sweep back and forth like a biological metal detector to find lunch lurking on the seabed. They even enjoy munching on stingrays, oblivious to their deadly barbs.
Some sharks lay eggs and some give birth to live young. They usually have relatively few babies (in fish terms) which makes them vulnerable species. Sharks can be pregnant for two whole years before they give birth, which is longer than whales or elephants. A few shark species give birth to just one or two 'pups' at a time, the successful offspring having eaten all their siblings inside the womb beforehand…
The phrase 'Jumping the Shark', meaning when something crossed the line into ridiculousness, originated on an episode of the sit-com Happy Days when lead character, the Fonz, inexplicably jumped over a shark on waterskis.
Shark attacks get lots of media attention, but humans kill an estimated 3 sharks every single second. Over Shark Week alone that will add up to some 1,848,000 sharks …
Willie Mackenzie is an Oceans Campaigner at Greenpeace UK.