This can be any type of snail. I'll go first: Seems like there is heavy air rain at Air Stone Road. Great Admiral Nerite is still chasing his offender. "A touch of air rain won't hurt, or tickle."
For context, this was meant to be a picture of Boris and Carrie the clownfish (UK readers will understand) but they got photobombed by my hawkfish and two turbo snails. The one on the right of the shot cleaned up those diatoms by himself in 24 hours.