Globose Duck Clam (Atlantic Surf Clam)
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Mactridae, Genus: Spisula, Species: Spisula solidissima · Mactridae (Trough shell family) · Bivalve, whole shell, rounded/oval shape
Species
Spisula solidissima
Shell Type
Bivalve, whole shell, rounded/oval shape
Family
Mactridae (Trough shell family)
Size
Approximately 2 to 3 inches in length visible in frame, which is medium-sized for this species. Adults typically range from 4 to over 7 inches.
Color & Pattern
Dull greyish-brown to charcoal coloration due to weathering and fossilization or beach wear. The original yellowish-tan periostracum is absent, revealing a monotonous grey exterior with dark linear shadows across prominent radial growth ridges.
Rarity
Common
Habitat
High-energy marine surf zones, intertidal to shallow subtidal waters, buried in coarse sand or fine gravel substrates along coastal ocean floors.
Geographic Range
Western Atlantic Ocean, from the Gulf of St. Lawrence in Canada down to Cape Hatteras, North Carolina, USA.
Description
A sturdy, thick-walled bivalve shell with a pronounced rounded profile and heavy, regular concentric growth lines. The prominent deep fracture running across the upper whorl indicates significant mechanical stress. The surface exhibits a coarse, weathered texture with strong ribbed radial patterns formed by centuries of tumbling or fossil-like aging.
Key Features
Thick heavy construction, deeply rounded convex shape, prominent concentric growth ridges crossed by fine radial textures, and an off-center umbo characteristic of the Mactridae family.
Collector Value
Low commercial or collector value due to the heavy weathering, lack of vibrant color, and prominent structural crack. Usually valued only as a study specimen or educational beach find rather than a display piece.
Condition Notes
Fair condition; shows significant structural damage with a major horizontal fracture across the upper valve. Heavily weathered with complete loss of original periostracum and color, making it more of a structural curiosity than a gem collector piece.
Interesting Facts
Spisula solidissima is commercially harvested along the US East Coast for the clam meat industry, particularly for clam chowder and fried clams. They use a powerful muscular foot to dig rapidly back into the sand if exposed by surf.
Ecological Role
Serves as an important benthic filter feeder processing nutrients from the water column. Acts as a vital food source for bottom-feeding fish, sea stars, and predatory crabs.
Similar Species
Mactra exalbida or other surf clams in the Mactridae family; distinguished primarily by hinge structure details, shell thickness, and exact geographic provenance.
Beach Finding Tips
Look along high-energy sandy ocean beaches after heavy storms or nor'easters, especially near the surf line at low tide where heavy shells are deposited in shell-hash wrack lines.