Box Jellyfish
The box jellyfish is one of the most dangerous marine creatures in the world, thanks to its toxin which attacks the nervous system, heart, and cells of the skin. Its poison is so painful, that humans who get stung commonly die of heart failure or go into shock and drown before getting help. Box jellyfish have the look of a pale-blue semi-transparent bell, making them difficult to spot in the water. Each corner of the bell grows up to 15 tentacles, which each grow up to 10 feet long. These tentacles all have 5,000 stinging cells present on their individual surfaces.