it is an interesting thought, because in a sense, we are all like this, except the individual cells that make up our body are not able to survive on their own. but of course in The distant past, multicellular organisms came about due to single cell organisms working together.
anyway sorry to go off on one, I just thought it was in intriguing thought.
I can't actually think of any example to give you... unless....
well there is Legion from Mass Effect. sort of.