Atlantic Bay Scallop (also known as Calico Scallop)
Phylum: Mollusca, Class: Bivalvia, Order: Pectinida, Family: Pectinidae, Genus: Argopecten, Species: Argopecten irradians · Pectinidae (Scallop family) · Bivalve (two-shelled), whole shell, fan shape
Species
Argopecten irradians
Shell Type
Bivalve (two-shelled), whole shell, fan shape
Family
Pectinidae (Scallop family)
Size
Approximately 2 inches in width, which is average for this species. Adults typically range from 1.5 to 3 inches.
Color & Pattern
Mottled brownish-grey base with subtle reddish-brown rays and concentric growth lines on the exterior. The colors appear natural with minor sun-bleaching near the hinge.
Rarity
Common
Habitat
Found in shallow marine waters, typically in bays and estuaries, associated with eelgrass beds and sandy or muddy substrates in depths ranging from the intertidal zone down to 60 feet.
Geographic Range
Western Atlantic Ocean, from Nova Scotia down to the Gulf of Mexico and the Caribbean, commonly found along the eastern seaboard of the United States.
Description
A classic fan-shaped bivalve shell featuring rounded ears at the hinge and approximately 17 to 22 well-defined radial ribs. The surface displays a pleasing combination of earthy browns and tans, offering a tactile ribbed texture typical of active swimmers in the Pectinidae family.
Key Features
Nearly equilateral fan shape, approximately 17-22 strong radial ribs, and asymmetrical ears at the hinge line where the anterior ear is slightly larger than the posterior.
Collector Value
Low to moderate value. They are very popular for decorative crafts and general shell collections, though exceptionally brightly colored or pattern-unique variants can command higher interest. Typically sold in shell shops in quantity.
Condition Notes
Good condition. The shell is intact with minor natural wear along the margin, retaining much of its original color pattern. Collectibility grade is Good.
Interesting Facts
Unlike most bivalves that burrow or attach permanently, bay scallops can swim actively by rapidly clapping their valves together to expel water, jetting themselves through the water column. They also possess dozens of simple bright blue eyes along the edge of their mantle.
Ecological Role
Bay scallops play an important role as filter feeders, helping to maintain water clarity in estuarine ecosystems. They serve as a vital food source for numerous marine predators including rays, crabs, sea stars, and carnivorous gastropods. Populations can be heavily impacted by harmful algal blooms.
Similar Species
Pacific Calico Scallop (Argopecten ventricosus) and Atlantic Deep-Sea Scallop (Placopecten magellanicus). Distinguished by rib counts, geographic origin, and shell profile proportions.
Beach Finding Tips
Best found by beachcombing along sandy bay beaches and salt marshes at low tide, particularly after storms or heavy winds that wash up material from offshore seagrass beds.