Physalia utriculus

Physalia utriculus, also called Blue Bottle or (Indo-Pacific) Portuguese Man-of-War, is a marine hydrozoan of the order Siphonophora found in the Indian and Pacific oceans. A gas filled bladder allows it to float on the surface, propelled by currents, tides, and by a sail at the top of the bladder, which may be left or right-handed. A single long tentacle of venomous cnidocytes, hanging below the float, provides the animal with a means of capturing prey.

P. utriculus is distinguished from the Atlantic Portuguese Man o' War (Physalia physalis) by the smaller size of the float (six inches compared to twelve) and by having a single long fishing tentacle. Like its larger relative, P. utriculus often occurs in swarms. Also, like the Portuguese Man o' War, Physalis utriculus is not a jellyfish but a siphonophore, meaning that it is not a single animal, but a colony of tiny specialised organisms called zooids. The zooids that make up Physalia utriculus are all attached to one another and are linked to the extent that they all depend on each other for survival.