In the chamber where you grab the crystal there are giant bones wrapping around the room, this could be the bones to the infamous worm gods or ahamkaras. If you haven't seen it yet go to the mission and check it out . Its at the point where you kill the giant ogre that gets taken
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If you scan them, Ghost informs you that they are simply what the Hive use to dig their tunnels. These worms (not Worms, but worms) are referenced in Ghost Fragment: Ocean of Storms 2