Well. Actually, some guy saw me collecting a few snails and came back with a cup full of them. I didn't have the heart to throw them *all* out. I already had MTS, but they were light brown w/ spots. These buggers are dark brown. They dig, but I don't know if they're MTS or not. They don't seem to mind the lights nearly as much.
They haven't touched the plants yet. I see them hanging off of the plants, but they haven't put any holes or anything yet. Occassionally, I'll pluck off the ones on the glass to thin them down.
I don't really seem to notice a difference with or without them. Go figure. The puffer seemed pretty happy to have so many things to bite at. Once I start seeing babies, I'll probably start thinning them out hardcore.