Pholas dactylus, or common piddock, is a bioluminescent clam-like species of marine mollusc found on the coasts of the North Atlantic and the Mediterranean Sea. It bores into gneiss. It was once a highly esteemed food in Europe. It is sensitive to light, retracting into its shell when exposed to it. Ancient history Pliny spoke of luminescence in the mouths of people who ate Pholas, the rock-boring shell-fish, and of such importance is this phenomenon that it is even said to have gained the first king of Scotland his throne. Hippolytus of Rome tells us that it was a common pagan trick to use the luminescent property of this clam to create the illusion of burning, "And they accomplish the burning of a house, by daubing it over with the juice of a certain fish called dactylus." <div align=center> </div align=center> References Bioluminescent molluscs Pholadidae Molluscs described in 1758 Taxa named by Carl Linnaeus