Pholas dactylus is a luminescent clam-like species, of the genus Pholas, found on the Pacific coast of South America. It bores into gneiss

Gneiss

Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks.-Etymology:...

. 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

Pliny the Elder

Gaius Plinius Secundus , better known as Pliny the Elder, was a Roman author, naturalist, and natural philosopher, as well as naval and army commander of the early Roman Empire, and personal friend of the emperor Vespasian...

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 all Scotland his throne.