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) @sixpenceee