Pacific Giant Cockle or Egg Cockle
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Cardiidae, Genus: Clinocardium, Species: Clinocardium nuttallii · Cardiidae (Cockle family) · Bivalve (two-shelled), whole shell, heart-shaped or obliquely oval
Species
Clinocardium nuttallii
Shell Type
Bivalve (two-shelled), whole shell, heart-shaped or obliquely oval
Family
Cardiidae (Cockle family)
Size
Approximately 2.5 to 3 inches in length and width, which is average to moderately large for this species. Adults typically range between 2 to 4.5 inches.
Color & Pattern
The exterior exhibits a creamy-tan to light brown base color with subtle darker brownish-purple bands or streaks radiating towards the margin. The coloration appears mostly natural with slight weathering. The interior is typically a glossy white, sometimes with purple staining near the posterior margin.
Rarity
Common
Habitat
Found primarily in shallow subtidal and intertidal zones, buried shallowly in sandy, muddy, or fine gravel substrates within bays, estuaries, and protected coastal waters.
Geographic Range
Pacific coast of North America, ranging from the Aleutian Islands in Alaska down to southern California.
Description
A robust, inflated bivalve featuring strong, prominent radial ribs that number around 34 to 38. The shell has a distinctive heart-like cross-section when viewed from the end, with a high umbo and finely scalloped margins where the external ribs interlock at the edge.
Key Features
Distinguished by its high, prominent umbos, robust inflated shape, and a high count of prominent radial ribs (typically 34+) crossed by fine concentric growth lines, along with a distinct interlocking margin.
Collector Value
Low to moderate value. It is a very popular shell for beachcombers and beginner-to-intermediate collectors on the West Coast, usually valued between $2 to $10 depending on size and condition.
Condition Notes
The shell is intact with both valves present, displaying minor natural wear along the margins and slight sun-bleaching near the umbo. Overall condition is Good to Fine, suitable for a general collection.
Interesting Facts
Clinocardium nuttallii uses its strong, muscular, sickle-shaped foot not only to burrow rapidly into the sand but also to leap or pivot away from predators like sea stars.
Ecological Role
Serves as an important filter feeder helping to maintain water clarity, and provides a critical food source for numerous shorebirds, sea otters, crabs, and bottom-feeding fish.
Similar Species
Loggerhead Sweetheart Clam (Protothaca staminea) or other cockle species, but distinguished by the higher rib count, more inflated shape, and distinct heart-like profile.
Beach Finding Tips
Look along Pacific Northwest and Northern California beaches and mudflats after winter storms or during extreme low tides, particularly near the mouths of protected bays and estuaries.