Mussels? Clams? Scallops?

[Biggest Little Reef]

Can anyone help identify these? I noticed the one on the left a while ago when the nearby rhodactis seemed to be shriveled up. Then this morning I noticed one of my other rhodactis bailed out and where it was I found another one. Could they be irritating my mushrooms? Should I consider removing whatever they are?

 

[GHOSTLY]

I have the same thing and I think its a clam

 

[J1a]

They might be brachiopods.

 

[Rtaylor]

Bivalves of some sort, good filter feeders, totally harmless to anything