Erm... ID Please???

[Nano]

maybe a parasite? (could be wrong)

[toytech]

they seem to be a type of limpet , i had some on my snails , kept there shell clean and never seemed to do any harm.

[reefgirl189]

I had one of these on an astrea snail too. I left it alone. Astrea is still alive and weird limpet thing went away.

http://youtu.be/R47t211KVmE

Turn your volume down, my dog starts barking in the video.

[ScubaSteve]

Looks to me like some sort of slipper snail (Credula sp.).