The Portuguese Man o’ War if a member of the Kingdom Animalia, phylum Cnidaria(1), class Hydrozoa, order Siphonophra, the genus Physalia, and the species Physalia(2).
The man-of-war is not an actual jellyfish, but a Siphonophor. Also the man-of-war is not a single organism. It is made up of many different 
organisms that work together. These organisms are called polyps.
The Portuguese man-of-war is usually found in the Northern Atlantic Gulf Stream. It can also be found in the tropical and subtropical regions of the Indian and Pacific Oceans.
The man-of-war will usually travel in groups, which may contain up to one thousand members.
The main portion of the man-of-war’s body is an oblong gas-filled bladder. The bladder is usually nine to thirty centimeters long, and is a translucent pink, blue, or purple. On top of the bladder is a crest. This is to catch the wind, and move the man-of-war along. Below the bladder, hang long stringy tentacles, which can reach a length of up to fifty meters. The tentacles are made-up of three different types of polyps. The names of these three polyps are: dactylozooid, gonozooid, and gastrozooid. The polyps are the parts that: capture prey, digest prey, and reproduce. The dactylozooids have cells called nematocysts(3). The nematocysts release a toxin(4) into anything that they come into contact with. The gastrozooids then attach to the dead/stunned victim, and spread over it. They digest it, and transfer food to the rest of the man-of-war. Last, the gonozooids create other polyps. The means, by which the man-of-war reproduces, however, is not yet understood.
The fish Nomeus gronvii lives among the tentacles of the man-of-war. This fish, which is eight centimeters long, is mostly immune to the man-of-war’s toxin. It will eat the tentacles, which will grow back, as its main source of food. Although it is mostly immune to the man-of-war’s toxin, the man-of-war will sometimes end up eating it.
The enemies of the man-of-war are the Nomeus gronvii, and the loggerhead turtle.
If you were to get stung by a man-of-war, you would experience a very painful sensation where you got stung. The toxin that the man-of-war uses blocks nerve conduction. This causes a severe systematic syndrome. This is accompanied by a fever, possibly shock, and interference with heart and lung functions.
Bibliography
“Portuguese man-of-war,” Encyclopedia Britannica. 1988, University of Chicago: Vol. IX, p.634-35
“Portuguese man-of-war,” Animal Kingdom. 1972, United States of America: Vol. XVIII, p.88-93
Caras, Roger. Venomous Animals of the World. United States of America: 1974, p. 17-18
hillside.sowashco.k12.mn.us, http://hillside.sowashco.k12.mn.us/kaipo/invertebrate/welcomeinv.html, United States of America: hillside.sowashco.k12.mn.us, 1997
Microsoft Encarta 1996. Silicon Valley Ca., Microsoft Corporation, 1997
1 Cnidaria and Celenorates are two interchangeable names for this Phylum.
2 Multiple sources were researched including the Encyclopedia Britannica, World Book, Encyclopedia Americana, Microsoft Encarta, and Internet searches through Yahoo, Altavista, and HotBot; however, no reference to Family was provided.
3 A capsule within specialized cells of certain coelenterates, such as jellyfish, containing a barbed, threadlike tube that delivers a paralyzing sting when propelled into attackers and prey.
4 A poisonous substance, especially a protein, that is produced by living cells or organisms and is capable of causing disease when introduced into the body tissues but is often also capable of inducing neutralizing antibodies or antitoxins.
