Sentient, trianic-based energy beings who live in a dark-matter nebula and subsist off the neural energy of passing ship crews; Voyager's crew would have sustained them for years to come. They can, by choice, inhabit a body temporarily with no lasting damage, but a magneton flash will drive them out. They can also penetrate a ship's shield after a sustained effort.  As Voyager's shields were depleted with its sensors blind, Chakotay's disembodied neural energy inherited Neelix and arranged the stones on his medicine wheel to show the way out of the nebula.