It's the smallest jellyfish in the world. It's also one of the most feared, capable of delivering a sting 100 times as potent as that of a cobra and 1,000 times as strong as a tarantula.
Though it is most commonly found in the waters off Australia, it has been found in locations around the world, including Florida. Its size is roughly no larger than a cubic centimeter, which means that jellyfish netting often provided at beaches in Australia offer little protection, if at all.
Those stung by these teeny medusae suffer from what has been called irukandji syndrome, the symptoms of which include severe pains throughout the body, nausea, sweating, an increase in heart rate and blood pressure, and a constant feeling of impending doom. Yikes!