A range of jelly-like species are called box jellies. The name derives from the 4 distinct sides to the animal that give it a box like appearance. Box jellies are not true jellyfish because of this shape.
The larger species can inflict a sting that will severely injure or cause death to prey animals and humans. Each tentacle has about 500,000 cnidocytes, harpoon-shaped needles that inject venom into the victim.
The box jelly is clear or pale blue in colour making them extremely difficult to see in the water. In Northern Australia many swimming areas are closed during box jelly season.
Box jellyies can move more rapidly than other jellyfish, with speeds of up to six metres per minute, hunting its prey of zooplankton and small fish.