Metroids. What the fuck are they, and what do they do? Somehow, they cause your stomach to explode for no reason other than because of the xenomorph larva inside you. That only happens when you do certain things to them. Not clear what. They also eat things? They attack things if you hit them, so you should probably throw then down that disposal in Xenobiology, because it actually leads to that monkey pen on the other side of the room. Oh, I forgot to mention they spawn in that cage that takes up a third of Xenobiology.
So that's about it about Metroids?