SW snail question

[Kronk]

I had a huge population of nocturnal 1/4" snails that were obviously breeding as they eventually nearly covered every square inch of the glass at night but dissappeared during the day. There population dropped almost to zero when I moved a year ago but they seem to be building back up. They are like night time janitors its great I think the name starts with a C, columboidal... colonista ... or something like that...