Darkling

From Wikitroid, the Metroid wiki

Darkling is a Luminoth term used for describing Ing-possessed creatures and creatures that can only be seen on Dark Aether. This tends to greatly increase either their health or their attack, while making them highly vulnerable to light. Most Darklings have Aether counterparts, such as the Dark Splinter and the Splinter. The only way to seperate an Ing and its host without the Ing wanting to is to kill the host, and the Ing with it. It is unknown if any Darklings survived on Light Aether when Dark Aether collapsed, though it is a possibility, and it is known that at least one Darkling was kept as a specimen by the Space Pirates and dissected for research purposes. The Nightbarb is a odd darkling because the only Nightbarbs that aren't darklings are on Bryyo which is on another planet. It is a possibility that the Nightbarbs were on the Leviathan some way or another. It is also a possibility that the Nightbarb populations on Aether were very low when the Ing first experimented with possessing other lifeforms, and wound up rendering all normal Nightbarbs on Aether extinct. Another, more simple, theory is that the Nightbarbs are an original species from Dark Aether, having no light counterpart on Light Aether, though how they were created this way is uncertain. Darklings also seem to have the unique ablity to survive in Light Aether. This may be that they gain a resistance to light by posessing a creature that normally lives in Light Aether.