Atlantic Giant Cockle (also known as the Prickly Cockle)
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Cardiidae, Genus: Dinocardium, Species: robustum · Cardiidae (Cockle family) · Bivalve (Two-shelled); Fan-shaped/Heart-shaped when viewed from the side. This specimen is a single valve.
Species
Dinocardium robustum (Confidence: High)
Shell Type
Bivalve (Two-shelled); Fan-shaped/Heart-shaped when viewed from the side. This specimen is a single valve.
Family
Cardiidae (Cockle family)
Size
Approximately 3-4 inches in length. This is a mid-sized adult; the species typically ranges from 3 to 5 inches.
Color & Pattern
Base color is a yellowish-tan to greyish-brown with distinct concentrated reddish-brown or purple banding near the umbo (beak). The ribs show spotted or checkered patterns of brown. Interior is typically salmon-pink to reddish-purple.
Rarity
Common; frequently found on beaches along the Southeastern United States and Gulf Coast.
Habitat
Shallow subtidal marine waters, usually buried in sand just below the low-tide line. Prefers high-salinity oceanic environments.
Geographic Range
Western Atlantic from Virginia to the Gulf of Mexico and south to the Caribbean and Brazil.
Description
A large, sturdy, and inflated bivalve shell with approximatey 32 to 36 strong radial ribs. The shell has a rounded-triangular shape with a prominent umbo. The exterior is slightly rough to the touch due to the ribs, but lacks the sharp scales of some other cockle species.
Key Features
Strong radial ribs, lack of heavy spines compared to 'Prickly Cockles', distinctive reddish-brown banding near the hinge, and a yellowish-brown exterior with a pinkish-purple interior.
Collector Value
Low to Moderate. While beautiful and popular among beachcombers, they are very common. Larger or 'gem' condition specimens with vibrant interior colors are more desirable for formal collections ($2-$10).
Condition Notes
Good condition with some beach-wear. The color is slightly dull due to natural weathering and salt exposure. The hinge appears intact on this single valve, though the edges show minor chipping.
Interesting Facts
Cockles are known for having a strong, muscular 'foot' which they use to leap away from predators like starfish or whelks. Historically, they have been used as a food source in many coastal cultures.
Ecological Role
Suspension feeders that filter plankton from the water column. They serve as a vital food source for sea stars, shorebirds, and specialized predatory mollusks like whelks.
Similar Species
Trachycardium egmontianum (Florida Prickly Cockle) which is smaller and has sharp scales on the ribs, and Laevicardium laevigatum (Egg Cockle) which is smoother.
Beach Finding Tips
Found most easily after storms or during extreme low tides on sandy Atlantic and Gulf beaches. Look for large, heavy 'half-shells' in the wash line or shell piles.