Pacific Egg Cockle (also known as the Granulate Cockle)
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Cardiidae, Genus: Trachycardium, Species: Trachycardium procerum · Cardiidae (Cockle family) · Bivalve, single valve, fan-shaped to roughly circular outline with prominent radial ribs
Species
Trachycardium procerum
Shell Type
Bivalve, single valve, fan-shaped to roughly circular outline with prominent radial ribs
Family
Cardiidae (Cockle family)
Size
Approximately 1.5 to 2 inches wide, which is average for this species. Adults typically range from 1 to 3 inches.
Color & Pattern
Cream to light tan base color featuring striking dark brown to near-black zones, particularly concentrated along the posterior margin and posterior slopes. The radial ribs exhibit alternating light and dark markings, creating a checkered or dotted pattern.
Rarity
Common
Habitat
Found in shallow subtidal waters and intertidal zones, typically burrowing in fine sand, muddy sand, or sandy-gravel substrates in protected bays and marine environments.
Geographic Range
Eastern Pacific Ocean, ranging from the Gulf of California (Sea of Cortez) down along the coast of Central America to Peru.
Description
A robust, solid bivalve shell with a inflated, rounded shape. The exterior is heavily sculpted with dozens of strong, elevated radial ribs intersected by fine concentric growth lines, giving the surface a distinct textured, grid-like or granulate feel. The margin is deeply crenulated to interlock tightly with the opposing valve.
Key Features
Heavy radial ribbing with pronounced nodular or scaly texture, robust inflation, rounded to slightly asymmetric profile, and characteristic dark brown posterior patches contrasting with lighter tan and white ribs.
Collector Value
Inexpensive and widely available, making it a great staple piece for beginner shell collectors and beachcombers visiting the Pacific coast of the Americas.
Condition Notes
Good condition single valve. Colors are vivid and natural without major bleaching. Edges of the ribs show slight wear from wave action, but the overall sculptural integrity remains strong. Collectibility grade: Good.
Interesting Facts
Cockles are capable of using their muscular, sickle-shaped foot not only for burrowing into the sand but also for leaping or flipping themselves away from predators like predatory snails and starfish.
Ecological Role
Serves as an important benthic filter feeder, cleaning the water column by consuming phytoplankton. Forms a key food source for predatory gastropods, rays, and sea otters, playing an integral role in the nearshore marine food web.
Similar Species
Trachycardium consors (Desert Cockle), which tends to have more prominent spines and a slightly different geographic concentration; can be distinguished by specific rib counts and exact regional color variations.
Beach Finding Tips
Look along sandy beaches bordering the Gulf of California and the tropical Eastern Pacific, particularly at low tide following storms or rough wave action that uncovers burrowed bivalves.