After almost a year and a half I found some type of clam or mussel in a large zoa colony I have while looking at the tank at night after feeding some oyster-feast. I went through a bunch of ID sites and looks like some type of bi valve arc/ark clam but I am not 100%. It does open and close when light is shined on it. Anyway, I thought it was pretty cool. Center of pic, redish/purplish pattern on shell.