In Bungie's GDC panel, they were talking about enemies who, when you killed them, had their 'souls' fly out of their bodies. Not to mention that the art with the five races shows the Glimmer, and in the background you can see what is very likely to be a pyramid ship. You can also see their body type, which is a tall, slender figure with what appears to be a glowing head or face. I think these are all connected. The Glimmer are a tall, slender race that lives aboard the Pyramid ships, or at least uses them for a base of operations. And that they are the same creatures who's souls fly out of their bodies, due to the smoke in their picture.