Piddock Clams (Family: Pholadidae)

Description: When the sand levels are low at Haystack Rock, typically in the spring, portions of the bedrock are exposed. The mudstone bedrock 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-tipped 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 8 cm long, an off-white or gray color, and 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-tipped piddock 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 and other particles out of the water column.

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 4-5 mm per year.

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

Reference: ODFW, Walla Walla University, University of Oregon