Chiropsalmus quadrumanus
Chiropsalmus quadrumanus, commonly known as the four-handed box jellyfish, is a species of box jellyfish found in the western Atlantic Ocean, the Gulf of Mexico and the Pacific Ocean. The sting is venomous and dangerous to humans, especially children.
Irukandji jellyfish
Irukandji jellyfish ( ) are any of several similar, extremely venomous species of box jellyfish. With an adult size of roughly a cubic centimetre (1 cm), they are both the smallest and one of the most venomous jellyfish in the world. They inhabit the northern marine waters of Australia. They are able to fire their stingers into their victim, causing symptoms collectively known as Irukandji syndrome. There are about 16 known species of Irukandji, of which "Carukia barnesi", "Malo kingi", "Malo maxima", "Malo filipina" and "Malo bella" are the best-known.