The link above goes to Bungie's character development video from the Game Developers Conference. Pause the video around the 24 second mark and you'll see what I'm talking about.
I think it's either the "Glimmer" or a different class of the Hive.
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Its a Hive.
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This one? Seems like an 'infected' cabal to me. They have the same bulky body composure and legs.
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You see one of these things later on running with the Hive, the animation is the exact same. I don't know which video it is, but it's probably in Vidoc 2.
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Glimmer is the loot system, not an enemy.
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Its a Cabal.
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it looks like an early animation for the cabal