Cladus: Eukaryota Physalia is a genus of the order Siphonophora, colonies of four specialized polyps and medusoids that drift on the surface of the Indian and Pacific oceans. A gas-filled bladder resembling a blue bottle maintains their buoyancy, and a single long tentacle of venomous cnidocytes provide the animal with a means of capturing prey. A sail on their float, which may be left or right-handed, propel groups of Physalia about the sea. Individuals within these groups sometimes become stranded on beaches, where their toxic nematocysts can remain potent for weeks or months in moist conditions. The species are distinguished by the size of the float (six inches compared to twelve) and by having a single, or several long fishing tentacle. The species Physalia utriculus is given the common name Pacific Man o' war to distinguish it from the more widely distributed and larger Physalia physalis, the Portuguese Man o' war. No fatalities from envenomation are recorded for P. utriculus, in contrast to the larger species of the genus.[2] Species Physalia physalis The genus was first described by Jean-Baptiste Lamarck in 1801.[1] Diversity The family Physaliidae is described as monotypic, as it consists of only one genus, Physalia. The genus contains only two species.
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