How Can Something Be Both an Animal and a Colony?
It might look like a jellyfish, but it isn't. It might even look like a single organism, but it isn't -- not quite. The Portuguese man o' war is a kind of siphonophore, an order of creatures whose bodies are built in baffling ways. Siphonophores are made up of specialized multicellular building blocks called zooids. At first glance, zooids seem like regular cells: they're arranged in patterned formations that are specialized to certain tasks, much like the cells in an organ. In the Portuguese man o' war, there are four such formations, each specialized to floating, stinging, digestion, and reproduction, respectively. But zooids are also a lot like independent organisms. They can move independently, for one thing, and instead of dividing and duplicating like cells, they reproduce by budding. This makes siphonophores a lot like colonial organisms, such as coral. Scientists are still unsure whether to classify these creatures as one or many organisms.
Key Facts In This Video
There are about 175 species of siphonophores in the world, most of which live deep in the ocean. Some can reach lengths of 50 meters -- longer than a blue whale. (0:20)
A colony is defined as a group of organisms that work together but can function independently, whereas a single organism is composed of many interdependent units that can't survive on their own. The structures of siphonophores don't fit either definition. (0:38)
The fact they're made up of specialized building blocks called zooids makes them seem like single organisms, but because zooids can move independently and reproduce by budding rather than dividing and duplicating, they could also be classified as a colony. (1:10)