Atlantic Calico Scallop (also known as the Calico Scallop or Black Scallop due to fossilization)
Phylum: Mollusca, Class: Bivalvia, Order: Pectinida, Family: Pectinidae, Genus: Argopecten, Species: Argopecten gibbus · Pectinidae (Scallop family) · Bivalve (two-shelled), whole single valve, fan or disc-shaped
Species
Argopecten gibbus
Shell Type
Bivalve (two-shelled), whole single valve, fan or disc-shaped
Family
Pectinidae (Scallop family)
Size
Approximately 1.25 inches in width and length, which is average to large for a single valve of this species. Adults typically range from 1 to 2.5 inches.
Color & Pattern
Uniformly dark charcoal black to deep grey. This coloration is characteristic of fossilized or sub-fossilized shells (often referred to as 'iron-stained' or 'black' shells) buried in anaerobic, mineral-rich sediment layers rather than the typical mottled white, brown, and reddish calico pattern found in live specimens.
Rarity
Common overall as a living species, but the solid black fossilized or stained variant is an iconic and locally prized beachcombing find in specific Outer Banks locations.
Habitat
Found in shallow marine waters, typically living on sandy bottoms, seagrass beds, and offshore shoals from the low intertidal zone down to depths of 160 feet.
Geographic Range
Western Atlantic Ocean, ranging from Maryland down through Florida, the Gulf of Mexico, and the Caribbean Sea. The specific jet-black coloration is very typical of shells recovered from ancient fossil deposits exposed along the Outer Banks of North Carolina, such as Corolla.
Description
A classic fan-shaped bivalve with roughly 18 to 22 well-defined, rounded radial ribs radiating from the umbo (beak) to the scalloped margin. The ears (auricles) at the hinge are somewhat asymmetrical, which is typical for the genus. The surface exhibits coarse concentric growth lines crossing the strong ribs, giving it a tactile, deeply textured feel. The deep black mineral stain lends it a dramatic, obsidian-like appearance.
Key Features
Nearly equilateral fan shape, prominent and rounded radial ribs numbering around 20, unequal auricles (ears) at the hinge line, and the characteristic dark fossilized coloration unique to local geological strata.
Collector Value
Low to moderate commercial value, but high sentimental and regional collectibility. Beachcombers actively seek out the jet-black fossilized specimens from North Carolina beaches for display, crafting, or inclusion in specialized regional collections.
Condition Notes
Good to Fine condition. The shell is structurally intact with a well-preserved margin and unbroken ribs, showing minimal wear on the delicate edges. It is a sub-fossil specimen, meaning it lacks its original pearlescent interior luster but has achieved a stable, durable mineralized state.
Interesting Facts
Unlike most bivalves that remain stationary, scallops like Argopecten gibbus can swim actively by rapidly clapping their valves together to expel water, utilizing a series of dozens of tiny bright blue eyes along their mantle edge to detect light and shadow.
Ecological Role
As suspension feeders, scallops play an important role in filtering phytoplankton and organic particulates from the water column, improving water clarity. They serve as an important food source for bottom-feeding fish, rays, sea turtles, and marine mammals.
Similar Species
Atlantic Bay Scallop (Argopecten irradians), which tends to be slightly larger with fewer, flatter ribs (usually 17 or fewer) and lives in shallower, more sheltered estuaries rather than open marine waters.
Beach Finding Tips
Look along ocean-facing beaches in Corolla and the Outer Banks especially after winter storms, nor'easters, or beach nourishment projects that churn up offshore fossil layers. Scan the wrack line where heavy shells and pebbles concentrate.
Notes
Corolla, NC