Atlantic Giant Cockle (also known as the Heart Cockle)
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Cardiidae, Genus: Dinocardium, Species: Dinocardium robustum · Cardiidae (Cockle family) · Bivalve (clams/two-shelled); single valve specimen; heart-shaped when viewed laterally
Species
Dinocardium robustum (Confidence: 95%)
Shell Type
Bivalve (clams/two-shelled); single valve specimen; heart-shaped when viewed laterally
Family
Cardiidae (Cockle family)
Size
Approximately 4-5 inches in diameter. This is a large, mature specimen; adults typically range from 3 to 5 inches.
Color & Pattern
Dull beige-grey exterior with faint remnants of brownish banding. The shell appears significantly sun-bleached and weathered, losing its original glossy tan and reddish-brown mottling. The interior remains obscured but likely matches the exterior calcification.
Rarity
Common (beach-worn valves are very common, though whole double-valves in good condition are more prized).
Habitat
Marine; burrowing in sandy substrates in shallow subtidal zones to depths of about 100 feet. Prefers high-salinity ocean environments.
Geographic Range
Western Atlantic from Virginia to Florida, throughout the Gulf of Mexico, and south to Mexico.
Description
A robust, globose bivalve with roughly 22-28 prominent radiating ribs. The shell is thick and sturdy, possessing a characteristic inflated appearance. This specific specimen shows significant 'honeycomb' erosion caused by Cliona (boring sponges), creating a pitted texture across the surface.
Key Features
Distinctively large size for the family Cardiidae; strong radial ribs; deeply curved umbo (beak); heart-shaped profile when both valves are joined.
Collector Value
Low (nominal value). Common weathered valves are worth less than $1. Pristine, paired 'live-taken' specimens with full color can range from $5 to $15.
Condition Notes
Poor to Fair. The shell is a beach-worn 'dead' valve. It exhibits extreme bioerosion from boring sponges and is sun-bleached. The margins are slightly chipped, and the original periostracum/pigment is gone. Collectibility is for study rather than aesthetic display.
Interesting Facts
The living animal has a powerful, wedge-shaped foot that allows it to 'jump' across the seafloor to escape predators like starfish and whelks. Historically, these shells were used by Native Americans as scrapers and containers.
Ecological Role
Suspension feeder that filters plankton and nutrients from the water column. The empty shells, once bored by sponges (as seen here), provide micro-habitats for small marine invertebrates.
Similar Species
Laevicardium elatum (Giant Egg Cockle) which is smoother and larger; Trachycardium egmontianum (Prickly Cockle) which has sharper, scaly ribs.
Beach Finding Tips
Look for these on sandy Atlantic beaches after strong storms. They are heavy and often wash up near the high-tide line. Best found in the southeastern United States, particularly Florida and the Carolinas.