snails/worms? living on my astrea snails?

[fmelindy]

yeah, I had the exact same thing in rather large numbers living on the shells of my turbo snails. Didn't seem to harm them at all and I observed them picking at the rocks as you did. They also seemed to move over the shell and even kept the shells clean. Too bad I didn't get pics of them. I just assumed they were like some kind of "hitch-hiker snails" but I'm curious as well..