The Portuguese Man-of-War, or Physalia physalis ( in Greek this means air bubble ) is most often thought of as a jellyfish but in fact it is not in the true jellyfish at all. It belongs in the family of Hydrozoans.

Another common error is that that it is thought to be a single organism. The truth is that a Man-Of-War consists of four different organisms.

Pneumatophore - This is the gas filled float, or baloon looking portion, that glides on the surface of the water. It is a modified version of a polyp and is inflated with a carbon monoxide gas.

Dactylozooids - These are the tenticles that extend down below the float. They are the mechanism that catches, stings, and brings its food to the feeding organism. 

Gastrozooids - This is the 'digestive' organism. Think of it as an elongated, external, hollow mouth that extends itself to encompass the food item. 

Gonozooids - These are the reproductive organisms. 

For as feared as the Man-Of-War is, especially by other fishes, there is one fish ( Nomeus sp.) that is immune to the stinging tenticles. This fish spends most of its time amougst these tenticles either for protection, or possibly as a decoy to lure in other fishes.

Midwater Systems has developed a custom acrylic jellyfish tank, called the Jelliquarium, and is working on holding systems used to keep these midwater collections and gelatinous organisms in suspension.

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