Species

Indo-Pacific Man-O-War

Physalia utriculus, (Gmelin, 1791)

marine

About Indo-Pacific Man-O-War

Physalia utriculus, also called bluebottle or Indo-Pacific Portuguese man o' war, is a marine hydrozoan of the order Siphonophorae found in the Indian, Atlantic, 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. A single long tentacle of venomous cnidocytes, hanging below the float, provides the animal with a means of capturing prey. They can cause painful injuries to humans when encountered at beaches, on which they are sometimes stranded in large numbers.

Appearance

Like the Atlantic man o' war, Physalia physalis, the Indo-Pacific Portuguese species resembles a jellyfish but is a siphonophore, a composite of specialised organisms that function cooperatively. It is composed of four separate colonies of polyps and medusoids. The colony consists of a gas-filled polyp that keeps it afloat, and three other polyp types called the gastrozooids, gonozooids and dactylozooids. Dactylozooids form tentacles that hang below the water's surface and detect and attack prey, and drag the prey towards the gastrozooids for digestion. The gonozooids are adjacent to the gastrozooids and constitute the reproductive structures of the colony, dispersing eggs or sperm.

Habitat

Physalia utriculus is less widely distributed than the larger P. physalis, but it is the most common species on Australian coasts. It is also found in Hawaiian waters, where it is informally named ‘ili mane‘o or palalia.

Where to see it

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