What's growing on my snails?

[Lexie217]

This lump was on the snail when I got him but it was a lot smaller. The snails seems happy and travels around the tank so I don't think it's hurting him. It is growing though and I'm curious to know what it is.

 

[namfuak]

Looks like a Slipper Limpet (Crepidula) to me. I have one on one of my Astraea snails as well. It's a harmless filter feeder and I wouldn't attempt to pull it off.