Dust shield???

[craiggotgame]

I have no idea if that is what this thing is called. I was driving about a week ago on the highway when I heard this loud wind sound like someone opened a window. When I stopped to investigate a large fiberglass piece that sits under my engine had falled down on one side. There was a bolt that was missing. I had just got my oil changed 2 days before and I thought that maybe this piece needs to be removed for the oil change, and they forgot to put it back on, but when I took it to my mechanic he sad the bolt had been sheered off by bottoming out. I have only bottomed out once, very mildly, since I have owned the car. Anyway he was able to get it back up but it is all broken up now, and he said that it will probably fall agiain so I will have to replace it pretty soon. What purpose does this piece serve? What is it called. Could I order one from partshop? Please help guys.