Okay, a couple of things I found wrong with the "how to get" of this (this being the Shellbug Chitin, the rather unique ingredient that comes from Shellbugs, and is used in forging the Shellbug Helmet). I'm not sure if starting this page was right - I've never done anything like this before - but it's only a talk page, so what the hell. First of all, the cave it is located in, at least in my experience, (maybe there is more than one Shellbug in the game?) was "Sharpslope Cave", not "Forgotten Vale Cave", though obviously Sharpslove Cave is located in Forgotten Vale. Second of all, it was not hidden in a room that needed a lever to move the stone door, though it was hidden in a room that was out of the way and not too noticeable, no stone door was guarding it nor did I even see a lever anywhere in the cave. The thing that led me to finding it was the sound it was giving off-- definitely not like anything else I've heard in Skyrim, so I knew something unique was probably near. When I found it, I didn't even realize it was the shellbug, as the cave it was located in was not the same one the actual article for this said, but after hitting it a few times with the crossbow, I tried to mine it, and sure enough, I got 3 Shellbug Chitin and a regular Diamond.
So, I felt this needed to be shared, so I went ahead and shared this story. Maybe it shows that there IS more than one shellbug in the game, or maybe it shows that the information in the article was wrong.. I guess I'll know eventually.
I can now confirm that there are at least two Shellbugs in the game, as I looked around and located the Forgotten Vale Cave and found the Shellbug in there behind the stone door. I will update the Shellbug Helmet page and have already updated the Shellbug page. If you find anymore, let me know.
This helmet kind of reminds me of the helmet that dunmer wear in the original description of their armor