Box jellyfish
Box
jellyfish (class Cubozoa) are cnidarian invertebrates distinguished by their cube-shaped medusae. Box jellyfish are known for the extremely potent venom produced by some species.
Chironex fleckeri, Carukia barnesi and Malo kingi are among the most venomous creatures in the world. Stings from these and a few other species in the class are extremely painful and sometimes fatal to humans.
"Box
jellyfish" and "sea wasp" are common names for the notoriously dangerous Chironex fleckeri. However, these terms are ambiguous, as "sea wasp" and "marine stinger" are sometimes used to refer to other box jellyfish.
The box jellyfish actively hunts its prey (zooplankton and small fish), rather than drifting as do true jellyfish. They are capable of achieving speeds of up to 4 knots (7.4 km/h; 4.6 mph).
Each tentacle has about 500,000 cnidocytes, containing nematocysts, a harpoon-shaped microscopic mechanism that injects venom into the victim. Many different kinds of nematocysts are found in cubozoans.