Covern

From Wikitroid, the Metroid wiki

Coverns are enemies that appear in Super Metroid in the Wrecked Ship. Their body only consists of skulls. They were once sentient life-forms that died in the crash, but their souls did not leave the ship for some reason. Angry about the fact that they died and could not move on, they decided to drain the life from all who dared to enter the ship. Once Samus has defeated Phantoon, they are no longer encountered, possible due to it having controlled them and prevented them from "moving on".