The coelacanth is known as a “living fossil” because it looks very much like its ancestors from 300 million years ago. Its genome has been sequenced, and it, in fact, has been found to be evolving at a very slow rate. The genetic sequence also might help give some insight into the transition from fins to limbs.

The new species is member of the arapaima genus, which contains some of the world’s biggest freshwater fish that breathe air and weigh up to 200kg. Found in the central Amazon of Brazil, the new fish has been named Arapaima leptosoma and is the first new species of arapaima described since 1847.

Found all around the world, including off the coast of Australia, the tripod fish can live in depths of up to 6 km below the surface. The purpose of those super-long fins is to elevate the tripod fish to about a metre above the seabed, where the ocean's current is strong. This means that small prawns and crabs are ushered right into the tripod fish's gaping mouth, and all it has to do is stand there.

Penguins may lack teeth, but they have backward facing spines in their throats that grip and guide fish down.

The angry-looking deep sea angler fish has a right to be cranky. It is quite possibly the ugliest animal on the planet, and it lives in what is easily Earth's most inhospitable habitat: the lonely, lightless bottom of the sea.

There are more than 200 species of anglerfish, most of which live in the murky depths of the Atlantic and Antarctic oceans, up to a mile below the surface, although some live in shallow, tropical environments. Generally dark gray to dark brown in color, they have huge heads and enormous crescent-shaped mouths filled with sharp, translucent teeth. Some angler fish can be quite large, reaching 3.3 feet (1 meter) in length. Most however are significantly smaller, often less than a foot.

Their mouths are so big and their bo ...

The arapaima (Arapaima gigas) is one of the biggest freshwater fish on the planet and has evolved a multi-layer defence against the piranha. Its scales have an ultra-tough outer shell, which promotes tooth fracture at the point of penetration. The scales are also a corrugated shape, which deflect pressure to overlapping layers of collagen underneath.