Introduced in the Burning Crusade expansion pack. The Primordial Aspects are probably a group of elementals that instead on focusing on the things like fire and air, focus on unique aspects of nature like the night and poison. The only one in game is Murmur, the Primordial Aspect of sound, a boss in the Shadow Labyrinth wing of the Auchindoun instance.

Note that they may not be elementals but in fact elemental-like beings. Murmur is listed as an elemental for game mechanics.