Portuguese man-of-war tentacles

The Portuguese man-of-war, Physalia physalis (Siphonophorae - Physaliidae) stands out for its beauty, its deadly effectiveness, and its composition. This is not a jellyfish, but a siphonophore, which takes form and function through the aggregation and physiologic integration of numerous individual zooids, each small and specialized, scarcely capable of life on its own. It is the organization of zooids into polyps that enables the man-of-war to float, feed, reproduce, and sting.

The Portuguese man-of-war is found in the Pacific and Atlantic oceans and consists of a floating colony composed of several types of polypoid individuals attached to a free-floating stem. It has very long tentacles (as long as 30 m), has a large float containing nitrogen and carbon monoxide, and has up to 750 000 nematocysts on each of its 40 tentacles. 

Envenomation by Portuguese man-of-war stings may cause fatalities due to respiratory failure and hypotension. Physalia physalis toxins cause hemolysis, mast cell degranulation, vasodilation, and conduction disturbances.

References: [1] - [2] - [3]

Photo credit: ©Alvaro Migotto | Locality: CEBIMar, University of São Paulo, Brazil (2006)

The siphonophoreLilyopsis fluoracantha sp. nov. (A) Whole animal in approximately lateral view. The nectophore drawn on the left is pointing slightly out of the page, and the one on the right is pointing into the page; (B) lateral view of a bract and cormidial bell from the bract’s right side. Spur and gastrozooid are shown only for orientation, and do not accurately represent their positions; (C) upper view of the bract. Note that the bract comes to sit on the dorsal side of the stem. Abbreviations: anterior (An); posterior (Po); bracteal left (BrL); bracteal right (BrR); somatocyst (so); hydroecium (hy, fine dashed line); pedicular canal (pc); right lateral canal (rlc); left lateral canal (llc); upper radial canal (uc); lower radial canal (loc); red pigment spot (rp); marginal tubercule (tu); bract (br); stem (st); cormidial bell (cb); spur (sp); gastrozooid (gz); longitudinal bracteal canal (lnc); lateral bracteal canal (lac); upper bracteal canal (ubc); anterior hydroecial canal (ah); posterior hydroecial canal (ph).

Haddock, SHD, CW Dunn, and PR Pugh (2005) A reexamination of siphonophore terminology and morphology, applied to the description of two new prayine species with remarkable bio-optical properties. J. Mar. Biol. Assoc. U.K. 85:695-707. doi:10.1017/S0025315405011616 (pdf)

"Diagrams of siphonophore structure. The anterior end is up unless otherwise noted. The stem can be divided into two regions, the nectosome (which bears the nectophores that propel the entire colony) and the siphosome (which bears all other zooids). Scale bars are approximate. (a) A cystonect, Rhizophysa eysenhardti, scale bar = 2 cm (adapted from Kawamura, 1910). Cystonects have a pneumatophore and a siphosome, but no nectosome. (b) Agalma elegans, scale bar = 2 cm (adapted from Totton, 1954). This species has traditionally been placed in the Physonectae, a grade taxon that includes species with a nectosome (except Athorybia), a siphosome, and a pneumatophore. (c) A calycophoran, Rosacea flaccida, scale bar = 1 cm (adapted from Biggs et al., 1978). Calycophorans have a nectosome and a siphosome, but no pneumatophore. (d) Lateral view of a portion of siphosomal stem from the physonect Agalma okeni (adapted from Bigelow, 1911) showing some zooids in detail, scale bar = 2 mm. The figured region is part of a series that repeats, with only slight differences, along the entire length of the siphosome. Lateral view (e) and view from the lower surface (f) of a detached nectophore of Halistemma rubrum, scale bar = 5 mm. Nectophores aremedusae that are specialized for propulsion, and contraction causes water to exit from ostium, which faces to the left in these figures. The nectosac (subumbrella) is indicated by stippling. Nourishment is provided from the stem by a series of canals, which sometimes include the descending pallial canal (DPC). The point of attachment (PA) to the stem is also shown. B, bract; GA, gastrozooid; GD, gonodendron (a compound reproductive structure consisting of gonophores, palpons, and special nectophores that propel detached gonodendra but not the entire colony); GO, gonophore; N, nectophore; P, palpon; Pn, pneumatophore; T, tentacle (of the gastrozooid)”

Dunn, CW, PR Pugh, and SHD Haddock (2005) Molecular phylogenetics of the Siphonophora (Cnidaria), with implications for the evolution of functional specialization. Systematic Biology 54:916-935. doi:10.1080/10635150500354837 (pdf)


Despite its outward appearance, the man o’ war is not a jellyfish but a siphonophore, which differs from jellyfish in that it is not actually a single organism, but a colonial organism made up of many minute individuals called zooids. Each of these zooids is highly specialized, and, although structurally similar to other solitary animals, they are attached to one another and physiologically integrated to the extent that they are incapable of independent survival.

The name “man o’ war” comes from the man-of-war, an 18th-century armed sailing ship, and the cnidarian’s supposed resemblance to the Portuguese version at full sail.

The Portuguese man o’ war lives at the surface of the ocean. The gas-filled bladder, or pneumatophore, remains at the surface, while the remainder is submerged. Since the man o’ war has no means of propulsion, it is moved by a combination of winds, currents, and tides. Although it can be found anywhere in the open ocean (especially warm water seas), it is most commonly found in the tropical and subtropical regions of the Pacific and Indian oceans and in the northern Atlantic Gulf Stream. 

Physalia physalis, bluebottle or Portuguese Man O’ War by tanetahi on Flickr.

Physalia physalis, bluebottle or Portuguese Man O’ War

On the ocean-ward beach of Bribie Island, north of Brisbane in southeast Queensland. Despite dozens of them being washed up on the surf, there were children playing in the water.

They aren’t a true jellyfish, but a siphonophore, a colonial organism, and the venom is different to jellyfish venom. Vinegar makes it worse, the best treatment is hot salt water which denatures the venom

Okay, but why did we never learn about siphonophores in school?

I was aware of the Physalia Physalis, (and I think they’re super-cool), but I didn’t know there were so many different kinds of beings composed of multiple beings.  What the heck, biology class!  I think that might be a little more interesting/important than improperly dissecting fetal pigs.


Just look at these guys!


(Photos from and )