...a thing which was little more than a protoplasmic mass, from the body of which a thousand tentacles of every length and thickness flailed forth, from the head of which, constantly altering shape from an amorphous bulge to a simulacrum of a man's head, a single malevolent eye appeared.Here is some terrific video of a bioluminescent deep-sea siphonophore — an eerily fantastic creature that appears to be a single, large organism, but which is actually a colony of numerous individual jellyfish-like animals that behave and function together as a single entity. The individual units, called zooids, all share the same genetic material and each perform a specialized role within the colony."
"The best-known siphonophore is the poisonous Portuguese Man o’ War (Physalia physalis), which lives at the surface of the ocean, unlike the one shown in this video (filmed at a depth of 770 meters). Some siphonophore species can grow up to 40 meters (130 ft) in length." source