Ans: They are believed to have lived on earth for over a period of 650 million years, long before the dinosaurs which makes them the oldest multi-organ animal. The box jellyfish is said to be the most venomous and the deadliest jellyfish. It is said that its venom can stop a person's heartbeat within 2 minutes.A particular species in the jellyfish is capable of reverting back to its earlier life stage at any point in time. This jellyfish creature can be killed, but will not die of old age, hence the name is given as the immortal jellyfish.