Atlantic Bay Scallop
Phylum: Mollusca, Class: Bivalvia, Order: Pectinida, Family: Pectinidae, Genus: Argopecten, Species: Argopecten irradians · Pectinidae (Scallop family) · Bivalve (Two-shelled); Fan-shaped. This is a single valve (lower/right valve based on convexity and location data).
Species
Argopecten irradians
Shell Type
Bivalve (Two-shelled); Fan-shaped. This is a single valve (lower/right valve based on convexity and location data).
Family
Pectinidae (Scallop family)
Size
Approximately 1.5 to 2.0 inches (38-51mm) in height. This is a mid-sized adult fragment/valve; species typically reaches 3 inches.
Color & Pattern
Base color is off-white to cream with dark grey to charcoal mottling near the margins. Sun-bleached tan tones near the umbo (hinge). The ribs show a distinct darker pigment in the grooves, typical of beach-worn specimens found in the Carolinas.
Rarity
Very Common. These are frequently found on the beaches of North Carolina following storms or high tides.
Habitat
Found in shallow estuarine waters, particularly seagrass beds (eelgrass) and sandy or muddy bottoms. They are marine but can tolerate slightly lower salinity in bays.
Geographic Range
Western Atlantic from Cape Cod, Massachusetts to the Gulf of Mexico. Abundant along the North Carolina coast, including Holden Beach.
Description
A classic fan-shaped bivalve with roughly 17 to 22 radiating ribs. The ribs are rounded and prominent. The shell is nearly circular except for the 'ears' (auricles) at the hinge. The valve pictured has a slightly convex surface, characteristic of a scallop that lived on the seafloor.
Key Features
Rounded radiating ribs (plicae), equilateral shape (except for the ears), and the specific charcoal-grey and white color pattern common to the mid-Atlantic subspecies.
Collector Value
Minimal monetary value ($1-$5) due to high abundance. Desirable for local hobbyist collections or craft work, particularly specimens with vivid color variations (orange or yellow).
Condition Notes
Fair to Good. One 'ear' (auricle) appears chipped or missing. There is moderate beach wear/erosion on the ribs and hinge area. Significant sun-bleaching has dulled the interior luster, but the structural integrity is solid for a beach find.
Interesting Facts
Unlike most bivalves, the living animal has dozens of bright blue eyes along the edge of its mantle to detect movement. They are also unique for their ability to 'swim' by rapidly clapping their valves together to expel water.
Ecological Role
Filter feeders that improve water clarity by consuming plankton and organic detritus. They serve as a vital food source for sea stars, crabs, and humans. Protection of seagrass habitats is critical for their survival.
Similar Species
Calico Scallop (Argopecten gibbus) - usually more colorful with pink/purple spots and more convex valves; Rough Scallop (Aequipecten muscosus) - has small scales/spines on the ribs.
Beach Finding Tips
Best found at Holden Beach after a strong Northeasterly wind or at low tide near the inlets. Look in the 'shell hash' lines where the tide deposits smaller debris.
Notes
Holden Beach, NC