Pholas dactylus

This article is about the mollusc Pholas dactylus. For the band, see Pholas Dactylus (band).

Pholas dactylus, or common piddock, is a bioluminescent clam-like species of marine mollusc in the family Pholadidae.

Pholas dactylus
Shell of Pholas dactylus from Sicily on display at the Museo Civico di Storia Naturale di Milano
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Bivalvia
Order:	Myida
Family:	Pholadidae
Genus:	Pholas
Species:	P. dactylus
Binomial name
Pholas dactylus Linnaeus, 1758
Synonyms[1]
Pholas callosa Cuvier, 1817 Pholas callosa Lamarck, 1818 Pholas dactylina Locard, 1886 Pholas dactylus var. decurtata Jeffreys, 1865 Pholas dactylus var. gracilis Jeffreys, 1865 Pholas edwardsi Monterosato, 1878 Pholas hians Lightfoot, 1786 Pholas jordani van Hoepen, 1941 Pholas marmoratus Perry, 1811 Pholas muricatus da Costa, 1778 Pholas mytiloides Bory de Saint-Vincent, 1827 Zirphaea julan H. Adams & A. Adams, 1856

The piddock bores into the substrate for shelter, and lives in a tubular burrow formed by grinding the material away with hard parts of the shell by rotating on the longitudinal axis. It has been known to bore into the hard metamorphic rock gneiss, though it more often lives in softer rock. It is a filter feeder, using its siphons to reach the water outside the burrow. It was once a highly esteemed food in Europe.^[2][1]

Pholas dactylus: 1. Animal in the shell a) foot b) siphons c) inhalant orifice d) exhalant orifice. 2. shell e) accessory valves or plates

It is sensitive to light, retracting into its shell when exposed to it.^[3]

Distribution

The coasts of the North Atlantic and the Mediterranean Sea.

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.^[4] 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."^[5] In Bernard Cornwall’s ‘Excalibur’ Merlin daubs a girl in the juices from ‘Piddocks’ (a local British name) to give the impression of pagan divinity in a young girl.

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  Right valve
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  Left valve