Anyone seen this before?

Hello! Does anyone know what’s going on with this little guy? I marked NSFW bc I’m not sure if this is an injury/illness or not. His shell is just growing really weird. The growth is rough and hard, like he’s growing out of the old shell into a new, deformed one? I just wanna make sure he’s not sick or in pain. He acts normal though. Here’s some background info in case thats relevant: I’ve had them about 6 months. They live in a 20 gallon tank and I have coconut substrate for the bottom. They have sticks and moss that I collect from the same spot I found them and they always have fresh lettuce and cuttlefish bone. Thanks in advance for your help!