Box Jellyfish

Box jellyfish are invertebrates belonging to the class Cubozoa, named for their cube-shaped medusae. The Cubozoans are a categorized separately other types of jellyfish, and are considered more evolved; Scyphozoans. Likewise, the best-known species of box jellyfish, Chironex fleckeri, while sometimes simply called "the Box Jellyfish", is only one species of the category which actually contains about 19 different species. The name sea wasp is also applied to some species of cubozoans, including the afterforementioned Chironex fleckeri and Carybdea alata. Box jellies can be found in Australia, the Philippines, Hawaii, Vietnam, and many other tropical areas. Box jellyfish are extremely venomous and can kill.
Wiki Link: Box Jellyfish