The box jellyfish
The box jellyfish doesn't look dangerous. Floating in the oceans of Southeast Asia, it is hardly visible. But the box jellyfish can kill a healthy adult in less than three minutes.
Box jellyfish are invertebrates, which means they don't have a backbone. They have round bodies that look like upside down plastic bags. These bodies may be the size of a basketball but as they are transparent, they are very hard to see.
Jellyfish have 60 tentacles. Each tentacle is covered with special stinging cells.
The jellyfish hunts prawns and small fish by stretching out its tentacles. Because its poisonous feelers can stretch up to three metres, it has a long and dangerous reach!
A grownup box jellyfish has enough poison to kill 60 people. There is an antidote but it has to be given immediately.
Unfortunately very few people are saved. Box jellyfish poison burns the skin, affects the nervous system and causes a heart attack. If you're stung it hurts so much it's very difficult to swim to safety.