Most piddocks are large. The shell of Pholas dactylus, a European Atlantic species, may measure 15 cm (nearly 6"). The creature is luminous, to such an extent that one observer found that the immersion of a single piddock in half a pint of milk created a luminous glow sufficient to make faces recognizable in the dark; and that someone who chewed a piddock and kept it in his mouth would have luminous breath, as though breathing fire. The shape of the shells has produced some interesting local names, e.g. religieuse and bonne-sœur at Brest, where a resemblance was presumably seen to the headgear of certain nuns. Consumption of this piddock is desultory in most areas, but it has been eaten with enthusiasm in Brittany and the Channel Islands.