Flatworm or part of the snail?

[Davisc1293]

I cant tell what this is it appears to be on almost all of my snails in the same spot but look slightly different.

 

[reefz]

Kind of hard to tell from that photo but it doesn't look like a flatworm maybe just part of the snail. Flatworms only stay on coral, glass, and rocks. Any more photos?

 

[Isopod80]

That's the snails operculum. It's the door that seals the shell closed for protection when the snail retracts inside.