Nassarius Snail & eggs
Nassarius snails are an excellent snail for keeping the sand stirred up. They tend to hide, although you may spot their feeding tube extended up slightly like a periscope. When food hits the water, they quickly emerge completely and move quickly about the substrate.
Nassarius snails can breed in a tank, but their eggs rarely hatch out and turn into baby snails. The fish pick them off like caviar. This is their laying pattern, something that can be identified easily.
Here's another picture I took at a local fish store. I always look for opportunities like that. :)