That is an Electric Flame Scallop, Lima sp.
Its a very cool scallop. If you watch the mantels closely, you can see what looks like a bolt of electricity travel across it. It needs a good amount of flow and light for it to survive, as well and ampel amount of food. Most of these animals starve to death in the aquarium. If it doesnt like where its has been placed in the tank, or if it feel threatend, it will snap shut, forcing water out of its mantel, propelling itself through the water until it finds a spot that makes it happy.