Name that Species: Physalia utriculus

This weekend, I headed up the coast to Cape Campbell, where the Marine Ecology Research Group is running several long-term studies on the communities of the rocky intertidal zone. The next few posts will outline a bit of what we did up on the coast, and share a couple of species I came across.


This Portugeuse Man-O-War was a familiar find! I nearly stepped right on it, walking along the shoreline investigating things with my bare feet. Luckily I pulled my foot back in time and avoided the sting of this jellyfish colonial siphonophore. That’s right– it resembles a jelly (when not resembling a plastic bag), but the Man-O-War is actually a floating mass of distinct multi-cellular units called zooids. The zooids have divvied up the tasks of survival– some adapted to stinging, some to digesting food, some to reproduction, all living together in one happy lethal floating unit.

Onto the ID: As familiar as this creature looks, it is in fact a different species from the Atlantic Portuguese Man-o-War from home. That one is Physalia physalis, this is Physalia utriculus, or the Blue-Bottle/Indo-Pacific Portuguese Man-O-War. The common name comes from the warship-like appearance of the floating sac on the ocean surface, but seems especially apt to me for the fact that the siphonophore is colonial: just like a warship full of sailors working together, this Man-O-War is a unit composed of individual cooperating multicellular units*.

Until next time,


*Okay, okay, I have to confess– that metaphor is not entirely precise. While a navy man could survive as an individual off his ship, a single individual of this Man-O-War would die without the presence of the other zooids, since it’s specialized to the point of losing the ability to accomplish other tasks. Also, these zooids are for the most part genetically identical, unlike sailors on a warship. In that sense, they’re not so dissimilar from a multicellular animal, right? A human individual (for example) is made up of “individual” specialized cells with the same genetic information. Siphonophores are similar, but specialization is happening on the zooid level. To chew over the distinction more and juxtapose your worldview with that of an amoeba, check out this excellent post on siphonophores.

One thought on “Name that Species: Physalia utriculus

  1. I don’t know about the blue-bottle, indo-pacific variety, but I can assure that the Atlantic variety of Portuguese Men of War figured out how to make a kid howl. Years ago, I was on the scene when one washed up in the surf in Atlantic City, NJ (of all places!) trailing tentacles across my foot when I ran out to see what it was. I now run in the opposite direction ! Glad you didn’t step on that one !


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