The Man o’ War is sometimes thought of by the layperson as a jellyfish, but it’s not. It’s a colonial organism called a siphonophore. It consists of zooids that are each specialized, but come from the same fertilized egg and have the same DNA. That much I get from reading stuff.
But how are zooids different than human cells or organs? We also have cells and structures that are specialized for various purposes, but we don’t consider ourselves to be colonial organisms. The zooids can’t survive autonomously, at least to the best of my limited understanding (the only biology class I had was in the 9th grade).
I’m trying to wrap my head around what “colonial organism” really means.
Perhaps the difference is that zooids are created embryonically (meiosis) rather than through cellular division (mitosis). It would be like your lungs birthing another lung (I think).
Not if the eggs and sperm are contributed by zooids with the same DNA. (This is me spitballing with more confidence than I actually have in my conclusions)
Zooids may be highly specialized like organs, but they are derived from whole organisms, not cells. or think of it like this:
In a colonial organism, the parts are made of modified individuals.
In a multicellular organism, the parts are made of modified cells.
Colonies form not from a zygote developing into organs, but from asexual reproduction producing multiple organism-like modules that then specialize and integrate.
Livers never lived as independent organisms.
(side note : we’ll leave aside the next level of endosymbiotic cell organelles like mitochondria as outside the current problem)
There are also edge cases, like slime moulds, which shift from one to another.
Zooids of some hydrozoan cnidarians (“snail fur”) can survive and regenerate new whole organisms.
Then again, there are a number of species where some small fragment of an organism can survive and grow an entire new organism.
I suspect that the real answer is just that biology is messy, and it’s not always possible to draw clear boundaries as to what counts as “the same organism”, and the boundaries aren’t necessarily even drawn in the same fuzzy places for different cases.
Sure - either where specialized stem cells do it (like in flatworms) or where some surviving segments can do it. Not many where one single organ can regrow the whole thing, though. In Hydractinia echinata, a gastrozooid can regenerate into a whole new colony. That’s like your stomach having the ability to grow a whole new you.
Zooids are multicellular animals, so the parts also have parts. They’re cnidarians like jellyfish and coral, just that both morphotypes (medusae and polyps, respectively) are simultaneously present in the same organism.
PMo’W are made up of zooids who are all male or all female in the colony, and they reproduce sexually with gonophores and use asexual budding to build the rest of the colony. They’re essentially all clones within the colony, mutations aside.
The weirder thing for me is lichen, which consists of colonies of two different kingdoms, cyanobacteria and fungi.
In addition, zooidal organisms have no specialized circulatory systems to deliver either nutrients or oxygen, and to remove waste products. These are moved by diffusion from the speciality organ-like autozooids for feeding, digestion, and excretion. As noted, any collection of zooidal cells can reproduce the entire colonial organism, and for most zooidal organisms can reproduce by budding or division but they can also reproduce both asexually and sexually through dedicated reproductive systems. Zooidal animals are highly diverse and many species exhibit polymorphism (ability to grow into or convert to different forms). The Portuguese Man O’ War (Physalia physalis) is a pretty sophisticated siphonophore, capable of sexual reproduction and active, nervous-like rapid response to environmental stimuli despite being a colonial organism, but if you cut one up into many small pieces of a few cells each and kept it in a nutrient solution it would be able to regrow into the entire differentiated colonial organism.
