With a small sample of Piddocks, wrapped in seaweed and chilled to preserve them, we began to investigate the luminiscent properties of the Pholas Dactylus. The eyes must first become accustomed to total darkness for a few minutes and then the dull greenish blue glow of the opened mollusk becomes apparent. The glow is quite strong, clearly illuminating a glass of water and surroundings, and can last perhaps one day. The blue light offers a window into the world of the Piddock, a creature which spends its whole life in darkness, shunning daylight. Hands glow blue after touching the moist body of the Piddock, and if the raw Piddock is placed in the mouth the tongue and breath also glow blue, as indicated by Pliny in ancient Roman writings about the mollusk. The taste of the raw Piddock is equally as indescribable as this strange luminescence; an extreme chemical taste, perhaps stony or mineral, deep and prehistoric, very far from the usually mild seafood experience. All forms of cooking destroy the luminescence, though the raw Piddock can be preserved by freezing.
http://www.psychogeophysics.org/wiki/doku.php?id=piddock