The eponymous in-game Metroids are large jellyfish-like creatures with quadripartite nuclei. They are capable of siphoning an undetectable life energy from any animal, generally causing the death of the victim in the process. This energy can also be siphoned from the Metroid in turn, allowing it to be used as a living power source.
Now including a download link! Hooray! 😛
By Charles, tipped by Ryan