Almost everyone is familiar with the jellyfish known as the Portuguese Man-of-War (PMOW).  These large blueish colored jellyfish drift in the ocean extending their venomous tentacles into the water.  The sting of this creature is quite painful and though rare, has killed some people.  But they are not what you think they are.

Our common notion of jellyfish is a gelatinous creature with an umbrella like “head” and long stringy tentacles which can sting.  This type of jellyfish is called a medusa and though PMOW look and act like them – they are not.

The other form of jellyfish, which most are not aware of, is one known as a polyp.  Instead of having an umbrella-like head, polyps have a stalk-like structure that attaches to the seafloor – they sort of “stand on their heads”.  And instead of having long stringy tentacles extending behind them, their tentacles extend upward from the stalk giving them a “flower-like” appearance.  Because the stalk is attached to the seafloor they do not move (“swim” like their medusa cousins) but rather are stuck in one place (sessile).  The flower-like appearance can attract prey and their tentacles, like their medusa cousins, can also sting.  A classic jellyfish from this group would be the sea anemone.

PMOWs are certainly not polyps – they look nothing like this – so, they must be medusa.  But there you would be wrong… they are polyps.

Just as most people do not see Spanish moss being related to pineapples (they look nothing alike), PMOW do not look like sea anemones.  What is the deal?

Here is the deal…

PMOWs belong to a group of jellyfish called siphonophores.  These are actually large colonies of floating modified polypoid and medusoid individuals – it is not one jellyfish, but a colony of hundreds.  A characteristic feature of siphonophores is the large gas-filled sac, which is actually a modified medusoid member of the group.  The sac of the PMOW can be as long as 12 inches.  The structure of the sac is so that 50% of the population will “sail” 45° east of the wind, and 50% will sail west of it.  Some siphonophores can adjust the amount of gas within the sac so that they can sink below the surface during storms – this is not the case for the PMOW.

The tentacles are full of these small polyps, and each can extend their own tentacles armored with numerous stinging cells called nematocysts.  Each nematocyst contains a drop of venom used to paralyze their food.  The PMOW colony possesses hundreds of such polyps and possibly thousands of nematocysts with a very toxic venom.  They can paralyze and feed on larger fish than most medusa can.  And we all know their venom causes intense pain in humans.

So… the Portuguese Man-of-War… more like a floating colony of sea anemones than a medusa.  Many did not think that.

1