Physalia

Not to be confused with Physalis.

Physalia
Physalia physalis
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Cnidaria
Class:	Hydrozoa
Order:	Siphonophorae
Suborder:	Cystonectae
Family:	Physaliidae Brandt, 1835
Genus:	Physalia Lamarck, 1801
Species
Physalia physalis

Physalia is a genus of the order Siphonophorae, colonies of four specialized polyps and medusoids that drift on the surface of the Atlantic, Indian and Pacific oceans. Although these organisms look like a single multicellular organism, each specimen is actually a colony of minute organisms called zooids that have to work together for survival. A gas-filled bladder resembling a blue bottle provides buoyancy, and long tentacles of venomous cnidocytes provide a means of capturing prey. A sail on the float, which may be left or right-handed, propels Physalia about the sea, often in groups. These siphonophores sometimes become stranded on beaches, where their toxic nematocysts can remain potent for weeks or months in moist conditions. Both species of this siphonophore resemble a jellyfish in appearance, with their gas-filled float and cluster of polyps beneath, which can hang up to 30 or 165 ft (9 to 50 m) below the surface of the sea.

Because it frequently washes up on beaches on the coast of the Atlantic, Indian and Pacific Oceans and is seen in the open ocean, Physalia is the best-known genus of siphonophore, as nearly all siphonophores live in the cold, dark ocean depths where they can only be observed in their natural habitat by a submersible or ROV.

The genus was first described by Jean-Baptiste Lamarck in 1801.

Diversity

The family Physaliidae is monotypic, consisting of only one genus, Physalia. The genus is also monotypic, containing only P. physalis. There is a long history of the genus being described with multiple species, such as the Pacific man o' war (P. utriculus), however most of these species are now considered synonyms for P. physalis.