Surprisingly this isn't science fiction...but a marvel from the ocean right here on planet earth. Siphonophores are creatures, actually they are a colony of creatures, belonging to the same family as corals, hydrids and jellyfish. They are composed of several separate zooids (individuals)that are either medusae or polyps. Medusae are basically jellyfish and polyps are basically sea anemone. Each zooid in the colony has a specialized function of swimming or eating. Neither can perform the other, they are entirely dependent on the colony.
Census of Marine Zooplankton.
More detailed information and diagrams here.