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The wikipedia entry on the Portuguese man o' war says:

... the Portuguese man o' war is ... not actually a single multicellular organism but a colonial organism made up of many highly specialized minute individuals called zooids. These zooids are attached to one another and physiologically integrated to the extent that they are incapable of independent survival. (emphasis added)

This is contradictory. If it's got multiple cells, and those cells are highly specialized to the point of being incapable of surviving on their own, then how does that differ from a multicellular organism? That last sentence seems like it describes the cells in my body.

In fact, the entry colonial organisms says:

The difference between a multicellular organism and a colonial organism is that individual organisms from a colony can, if separated, survive on their own, while cells from a multicellular life form (e.g., cells from a brain) cannot. (emphasis added)

So, is the Portuguese man o' war a colony or a multicellular organism? And if it's a colony, can its zooids survive independently, the wikipedia text notwithstanding?

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Very related question:- biology.stackexchange.com/questions/8745/… –  Satwik Pasani Feb 20 at 10:29
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up vote 2 down vote accepted

Physalia and Siphonophorans in general are multicellular Metazoans.

But the whole discussion is about modularity on the level of individuals: Siphonophorans are colonial organisms, which means they are composed of multiple individual polyps and medusae. This is in fact quite common among Hydrozoa, but in Siphonophora the degree of integrity and function division among the components is of extraordinary level.

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I'll buy this, but it doesn't change the basic question. If they are so integrated, why aren't they simply considered a single organism like us? They derive from a single fertilized egg. They divide asexually from that egg. The individual cells take on specialized roles physiologically and structurally. Only one set of cells reproduces. Nothing about any of this suggests colony to me. Am I missing something? To me it just seems that because there are individual polypoid cells, people are hesitant to say it is one organism. –  single_digit May 5 at 13:41
    
I don't know, what you mean by "polypoid cells": individual modules here are zooids. No one is hesitant to call Physalia "one organism", but it's a colonial one, a very integrated modular animal. It is colonial from the morphological, developmental and evolutionary points of view. –  har-wradim May 5 at 16:18
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This is from National Geographic :

The man-of-war comprises four separate polyps. It gets its name from the uppermost polyp, a gas-filled bladder, or pneumatophore, which sits above the water and somewhat resembles an old warship at full sail. Man-of-wars are also known as bluebottles for the purple-blue color of their pneumatophores.

The tentacles are the man-of-war's second organism. These long, thin tendrils can extend 165 feet (50 meters) in length below the surface, although 30 feet (10 meters) is more the average. They are covered in venom-filled nematocysts used to paralyze and kill fish and other small creatures. For humans, a man-of-war sting is excruciatingly painful, but rarely deadly. But beware—even dead man-of-wars washed up on shore can deliver a sting.

Muscles in the tentacles draw prey up to a polyp containing the gastrozooids or digestive organisms. A fourth polyp contains the reproductive organisms.

Man-of-wars are found, sometimes in groups of 1,000 or more, floating in warm waters throughout the world's oceans. They have no independent means of propulsion and either drift on the currents or catch the wind with their pneumatophores. To avoid threats on the surface, they can deflate their air bags and briefly submerge.

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This does not really answer the question at all. –  kmm Feb 20 at 22:03
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