Any Ideas what is on my snail's shell?

[Central_FL_Reefer]

Looks like a small clam and something flat. Does anyone have any idea what is on this snail's shell?

 

[tbrown]

I forget what they're called... Slipper Snails or something? Harmless.

 

[ISpeakForTheSeas]

Yeah, looks like either a Calyptraeid snail (Slipper Limpets and relatives), or a Honeycomb/Foam Oyster (Gryphaeid bivalve).

Either way, they're harmless filter-feeders.