The Box Jellyfish

Believe it or not, a jellyfish can be a bigger threat to a human than the infinitely scarier looking shark. Specifically, it is the box jellyfish that poses the greatest threat to humans. This sea creatures has a body no bigger than a salad bowl but its tentacles can reach up to 15 feet long, and it can have up to 60 of them. Every tentacle contains enough toxin to kill around 50 adult humans. Over the last century, thousands of deaths have been attributed to this deadly animal. [Source]