Need an ID please

[EvilInSin]

We bought a Ricordia "rock" and later noticed the rics were on a dead clam shell. Well tonight (3 weeks later) we realized its not dead. It opens a bit and closes up tight if we touch it.
Here are pics
This is as open as it gets (under rather low lighting)

Top

Bottom

Is it a clam or oyster or what? I have no idea what to do with this thing, I just wanted the rics.
TIA

 

[OldmillXxX]

Looks like a totally encrusted oyster.

Cool!

Keep the pics coming.

 

[The steven liu]

It is an encrusted oyster, to keep it alive you should dose a good amount of phyto and zooplankton into your tank.

 

[chemisfun11]

Very cool encrusted oyster. I found that after I started using DT's my live rock became more alive and tiny little bivalves were perking up all over. It's amazing how some of these organisms are so tough

 

[JmLee]

eat it! eat it! na that is awsome! im jealous