Dark Luminoth

From Wikitroid, the Metroid wiki

A Dark Luminoth is a Luminoth that has been possesed by the Ing Horde. Many Luminoth, after finding out that the Ing Horde can even posses their own, had stated that they would rather "Self Terminate" than become a weapon for the Ing. Although they are mentioned in Luminoth Lore, they are not actually seen during gameplay as all of them had most likely been terminated.

Right is a screenshot of what appears to be a Dark Luminoth, seen in a beta trailer for Metroid Prime 2: Echoes; not seen in the full version. It is likely just an early model for the Luminoth, however.