Here are some close-up photographs of the Common Piddock – Pholas dactylus Linnaeus (Mollusca; Bivalvia; Pholadacea; Pholadidae) showing details that are important for its specific identification. The specimen in the first three images still has the dead animal within the shells. This is one that I collected from those I found at Monmouth Beach in Lyme Regis (see the previous post) where a slab of shale, complete with the rock-boring molluscs still inside the burrows, had been thrown up on the shore by stormy seas. The empty shell shown in images 4 – 8 is a beach-worn specimen picked up on Knoll Beach at Studland a few weeks ago.
Although the length of the shell of the Common Piddock can be up to 15 – 24 cm or 6 inches, the examples shown here are smaller – with an actual size of shell for the Monmouth Beach specimen of 50mm, and 108 mm in the shell from Knoll Beach.
Full details of the shell characters used for identification can be found in the references given below. This bivalve mollusc bores into sand, peat, marl, wood, shale, slate, chalk, limestone, red sandstone, schists, firm clays, and even thick old oyster shells, from low on the seashore to depths of a few fathoms. It occurs in The British Isles from Kent along the south and south-west coasts, including South Wales, and as far south as the Atlantic coast of Morocco. Of particular interest is the phenomena of phosphorescence or luminescence exhibited by the living animal which has has bioluminescent properties and glows with a blue-green light in the dark.
Earlier posts on Jessica’s Nature Blog that refer to the holes in rocks and pebbles made by piddocks and other seashore creatures include:
Rocks with holes made by Piddocks – Part 1
Beach Stones with Holes at Worms Head Causeway
Peat ‘pebbles’ with piddock holes
Pebbles with holes made by boring sponges
Pebbles with holes made by tube worms
Pebbles with holes made by sea creatures
Driftwood with holes made by Gribbles & Shipworms
Benjamin & the pebble full of holes
Shells with holes made by boring bivalves
A rocky beach near Portland Bill
Tebble, Norman (1966) British Bivalve Seashells – A Handbook for Identification, published for the Royal Scottish Museum by HMSO – Edinburgh, 2nd Edition 1976, ISBn 0 11 491401 X, pp 175 – 180. [Out of print but now available on CD from Pisces Conservation Ltd.]
Hayward, P. J., & Ryland, J. S. (Eds.) (1995) Handbook of the Marine Fauna of North-West Europe, Oxford University Press, 1998 reprint, ISBN 0 19 854055 8 (Pbk), pp 619 – 622. Still in print and available from Amazon and other booksellers.
MarLIN about Pholas dactylus
Wikipedia about Pholas dactylus
World Register of Marine Species about Pholas dactylus
Marine Species Identification Portal – about Pholas dactylus
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