|Shell of Pholas dactylus from Sicily on display at the Museo Civico di Storia Naturale di Milano|
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.
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.
- Gofas, S. (2012). Pholas dactylus Linnaeus, 1758. Accessed through: World Register of Marine Species at on 2012-02-23
- "Pholas dactylus (clam) - Britannica Online Encyclopedia". Britannica.com. Retrieved 2011-09-24.
- Selig Hecht (1927). "The kinetics of dark adapatation". The Journal of General Physiology. 10 (5): 781–809. doi:10.1085/jgp.10.5.781. PMC . PMID 19872361.
-  Author: Field Naturalists' Club of Victoria, Volume: v.21, 1904-1905, Subject: Natural history; Natural history, Publisher: [Melbourne] Field Naturalists Club of Victoria, Year: 1884, Possible copyright status: NOT_IN_COPYRIGHT, page 93
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