Wiktionary
box jellyfish
n. Pacific jellyfish of class Cubozoa.
Wikipedia
Box jellyfish
Box jellyfish (class Cubozoa) are cnidarian invertebrates distinguished by their cube-shaped medusae. Some species of box jellyfish produce extremely potent venom: Chironex fleckeri, Carukia barnesi and Malo kingi. Stings from these and a few other species in the class are extremely painful and can be fatal to humans.
Usage examples of "box jellyfish".
She surfaced with a translucent disc the size of her hand, trailing short tentacles that disquietingly resembled those of a box jellyfish.