Weird shell looking critter in qt tank

[Rickybobby]

Yes I have live rock in my qt tank the fish love it. The live rock just finished 30 days of coppersafe and a few snails have come out but this is new looks like a clam or something. It has moved around since yesterday hope these pics are ok

 

[Rickybobby]

Ooops here

 

[Rickybobby]

Copper hasn’t seen to hurt it lol

 

[Tired]

If you're certain it's moved under its own power and hasn't just been pushed around, maybe a slipper limpet.