Despite it’s size, the Irukandji jellyfish is believed to be the most venomous creature in the world. What’s more disturbing is that this tiny and extremely venomous jellyfish are found the world over. So far, there are two known species of Irukandji, the Carukia barnesi and the recently discovered Malo kingi. It’s size is roughly no larger than a centimeter cubed body and four tentacles which range from a few to 35 cm in length
The venom of Irukandji jellyfish results to Irukandji syndrome. This syndrome was first documented by Hugo Flecker in 1952. The symptoms includes severe pains at various parts of the body (typically excruciating muscle cramps in the arms and legs, severe pain in the back and kidneys, a burning sensation of the skin and face), headaches, nausea, restlessness, sweating, vomiting, high heart rate and blood pressure, and psychological phenomena (such as the feeling of impending death). Once a victim is stung, it will take an average of 30 minutes before the Irukandji syndrome sets in.
Here’s a documentary of the Irukandji jellyfish.