Hmmm... that's not sounding like a collonista... but of course I have a pic
Do you have nerites in there?
What snails DO you have in there.
I think I may know what you are talking about. I'll see if I can find an empty shell in the sand and I'll grab a picture. I see these small snails, white with black markings, very small, that never seem to grow up. I've not looked into getting it ID'd, but if I can grab a picture that is good enough for ID purposes I'll bring to someone who will know.
I'll also take some pics of the baby collonista snails.
But first I'll get the pic to you to see if it is similar (it'll have to be this evening cause the that tank is in the boy's room and they are not up by the time I get off work in the morning... well I guess the tank lights aren't on either