Pholas dactylus is a boring bivalve, approximately elliptical in outline with a beaked anterior end, up to 12 cm long. The shell is thin and brittle with a sculpture of concentric ridges and radiating lines. The shell is dull white or grey in colour, the periostracum yellowish and often discoloured. The siphons are joined and at least one to two times the length of the shell, white to light ivory in colour. Pholas dactylus has phosphorescent properties, the outlines of the animal glowing with a green-blue light in the dark.
- The shell is often thicker in older individuals, up to 2 mm thick in 12 cm specimens (E. Pinn pers. comm.).
- Although thin and brittle the shell of Pholas dactylus has a cross-lamellar design which efficiently deflects cracks away from the bulk of the shell which gives it the strength to burrow through soft rocks.
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