Cubozoans are marvelous
They look like your basic jellyfish, but they can swim pretty fast, maneuver around things, and see fairly well despite not having a brain. Believe it or not.
In general, box jellies are similar in form to the "true" jellyfish, known as scyphozoans. However, it is relatively easy to tell the two groups apart. Cubozoans have a square shape when viewed from above. (Gee, maybe that's how they got their name.) They also have four evenly spaced out tentacles or bunches of tentacles and well-developed eyes. Not surprisingly, given their squishy nature, there are not many fossil cubozoans known. Today, there are about 20 known species found in tropical and semitropical waters. The Australian stinger Chironex fleckeri is among the deadliest creatures in the world, having caused human fatalities.
If you're curious, you can learn a whole lot more about cubozoans.
Carybdeid from Darwin, Australia
Phylogenetic Position of Cubozoa
General Sources:Hamner, W. M., Jones, M. S., and P. P. Hamner. 1995. Swimming, feeding, circulation and vision in the Australian box jellyfish, Chironex fleckeri (Cnidaria,:Cubozoa). Marine and Freshwater Research 46 (7): 985-990.
Hamner, William, M. 1994. Australia's box jellyfish, a killer down under. National Geographic. August 1994.
Kinsey, Barbara. 1985. Barnes on box jellyfish. published by James Cook University of North Queensland.
Kinsey, Barbara. 1988. More Barnes on box jellyfish. published by James Cook University of North Queensland.
Larson, R. J. 1976. Cubomedusae: Feeding - functional morphology, behavior and phylogenetic position. in Coelenterate Ecology and Behavior, Mackie, G. O. ed., Plenum Publishing Co., New York.
Matsumoto, G. I. 1995. Observations on the anatomy and behaviour of the cubozoan Carybdea rastonii Haacke. Mar. Fresh. Behav. Physiol. 26, 139-148.