What is this thing?

[OceanSprayCranberry]

 

[Karen00]

Can you take a pic under white lights? It's hard to tell under blue. Does it have a hard shell and is it stationary? It almost looks like a clam of some sort.

 

[vetteguy53081]

It is often called a clam but is actually a bi-valve which is part of the scallop grouping and is a great filter feeder and generally not long lived although my three have been around for 3 years
Reef safe

 

[jshep13]

Looks like a clam to me. I have one too that came on my rock.

 

[Remy123]

Looks like a scallop of some sort to me