Pacific Giant Cockle (also known as the Egg Cockle)
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Cardiidae, Genus: Clinocardium, Species: Clinocardium nuttallii · Cardiidae (Cockle family) · Bivalve (two-shelled), whole shell, fan/heart shape
Species
Clinocardium nuttallii
Shell Type
Bivalve (two-shelled), whole shell, fan/heart shape
Family
Cardiidae (Cockle family)
Size
Approximately 3.5 inches in width, which is large and on the upper end of average for a beach-worn specimen. Adults typically range from 2 to 5 inches.
Color & Pattern
The exterior is entirely sun-bleached and weathered to a chalky matte white, with faint yellowish tinges near the growth zones. The natural color, which is usually brownish or yellowish-brown, has been completely eroded away due to sun exposure and beach tumble.
Rarity
Common in its native range, though finding a large, relatively intact single valve like this on certain beaches requires some searching.
Habitat
Found in intertidal and shallow subtidal zones, typically burrowing just beneath the surface in muddy sand, fine sand, or gravel substrates in protected bays and estuaries. Marine environment.
Geographic Range
Pacific coast of North America, ranging from the Aleutian Islands in Alaska down to San Diego, California.
Description
A robust, heavy bivalve featuring prominent, rounded radial ribs (typically around 34 to 38) radiating from the umbo to the margin. The shell has a distinctive heart-shaped cross-section when viewed from the side, though only a single valve is shown. The exterior displays deep concentric growth lines intersecting the strong radial ribs, creating a subtly textured, scaled appearance in living specimens that is largely smoothed out here due to wear.
Key Features
Distinguished by the high number of prominent radial ribs (usually 32-38), a somewhat rounded to sub-quadrate outline, and prominent, slightly inrolled beaks (umbones) positioned near the center of the hinge line.
Collector Value
Low to moderate commercial value as it is very common, but desirable for regional shell collections representing the Pacific Northwest marine fauna. Typically valued at a few dollars.
Condition Notes
Good grade for a beach find. The shell is structurally sound with intact margins and visible ribbing, but it is heavily sun-bleached (pure white), missing its original brown periostracum and pigmentation, and shows minor edge wear.
Interesting Facts
Like other cockles, Clinocardium nuttallii uses a powerful, muscular, sickle-shaped foot to dig rapidly into the sand or even leap away from predators like starfish.
Ecological Role
An important filter feeder that helps clear coastal waters of phytoplankton. It serves as a key prey item for sea otters, diving ducks, gulls, and predatory gastropods.
Similar Species
Spiny Cockle (Vepricardium asiaticum) or other Pacific cardiids, which can be distinguished by fewer or sharper spines and different geographic distributions.
Beach Finding Tips
Look along protected Pacific Northwest sandy or muddy beaches, particularly near the low-tide line in bays and estuaries after winter storms.