Jellyfish have been around for some 500 million years. The key to their survival is adaptability and they come in all shapes and sizes, from the minute to the massive. The gigantic Lion's Mane jellyfish of the northern Pacific waters can grow to more than 30 metres long.Many have poisonous tentacles and the deadliest of them all is the Box jellyfish.It is one of the most dangerous creatures in the world, whether on land or in water, and is found off the coast of parts of Australia.Their deadly sting has prompted researchers there to study their DNA to find out more about their breeding cycles and venom