Whats growing on my rock?

[Paddypils]

Hi guys,
Could anyone id this? It looks like a tiny clam and reacts to light, when i hold something over it it closes.

 

[G Santana]

Cool bivalve!!!

 

[vetteguy53081]

These bivalves are safe and are members of the scallop group and filter feed particulate from the tank. Generally not long lived but I have one at least 3 years that is now 2+" long