Piddock Clams (Family: Pholadidae)

Description: When the sand levels are low at Haystack Rock, typically in the spring, portions of the bed rock are exposed. The mudstone bed rock is covered in holes created by piddock clams that have bored into the ground. Two species of piddock clams can be found at Haystack Rock. The flat-tip Piddock (Penitella penita) is commonly found around the base of Haystack, and rough piddock clams (Zirfaea pilsbryi) are also sometimes present. The clams themselves are not typically visible, within their burrows but these clams are around 8cm long, are an off white or gray in color, and are covered in ridges. Both species use the rough ridges on the outside of their shells to carve away rock or mud and create holes for them to live. Piddock clams can live for more than 20 years if their rock substrate is not disturbed.

Habitat: The flat-tip ranges from Alaska to Baja California, Mexico and the rough piddock ranges from Alaska to Southern California. Both species are found in the intertidal to subtidal zones, and typically bore into mud, sand, or soft rock.

Diet: Like other bivalves, piddock clams are filter feeders and eat plankton.

Tide Pool Tidbits:

• Piddock clams are sometimes called angel wings because of the shape of the shells when they are open.

• The flat-tipped piddock can bore between 4 and 5 mm per year.

• Piddock clams have the ability to bore into substates as strong as concrete.

Reference: ODFW, Walla Walla University Invertebrates Database, Oregon Institute of Marine Biology