Atlantic Bay Scallop (also known as the Common Scallop or Bay Scallop)
Phylum: Mollusca, Class: Bivalvia, Order: Pectinida, Family: Pectinidae, Genus: Argopecten, Species: A. irradians · Pectinidae (Scallop family) · Bivalve (two-shelled), whole individual valve, fan-shaped
Species
Argopecten irradians
Shell Type
Bivalve (two-shelled), whole individual valve, fan-shaped
Family
Pectinidae (Scallop family)
Size
Approximately 2 inches in width, which is a standard adult size for this species. Adults typically range from 1.5 to 3 inches.
Color & Pattern
Remarkably vibrant and unusual color split, featuring a deep solid purple on one side transitioning to a mottled orange, brown, and white pattern on the other side. Note that while natural variations include white, yellow, orange, and purple, this specific intense dual-tone coloration or gloss may indicate it has been artificially polished, treated, or is an exceptional natural color morph.
Rarity
Common overall as a beach shell, but specific intense color morphs like bright solid purple or unique split colors are considered uncommon and desirable finds for beachcombers.
Habitat
Found in shallow marine waters, typically in shallow bays, estuaries, and grass beds attached to eelgrass or lying on sandy-mud substrates.
Geographic Range
Western Atlantic Ocean, ranging from Nova Scotia down along the Atlantic coast of the United States to the Gulf of Mexico, including the Caribbean.
Description
A classic fan-shaped bivalve featuring approximately 17 to 22 distinct, well-rounded radial ribs. The hinge area shows distinct, relatively equal-sized auricles (ears) typical of scallops. The margins are scalloped to match the exterior ribs, creating a strong, interlocking seal when closed.
Key Features
Nearly equilateral fan shape, prominent equal-sized auricles at the hinge, rounded radial ribs (fewer than related species like the calico scallop), and distinct color zoning.
Collector Value
Low to moderate commercial value, but highly valued by casual beachcombers for crafts and decorative collections due to their bright colors. Standard specimens are inexpensive, but rare bright purple morphs can command higher interest.
Condition Notes
Good to Fine condition. The valve appears structurally intact with well-defined ribs and margins, retaining a glossy surface finish, though lack of natural matte texture may suggest minor surface oiling or buffing.
Interesting Facts
Scallops are unique among bivalves because they can swim by rapidly snapping their shells together to expel water, propelling themselves through the water column. They also possess up to 60 tiny, bright blue eyes along the mantle edge that can detect light and movement.
Ecological Role
Bay scallops are important filter feeders that help maintain water quality in estuarine ecosystems. They serve as prey for various crabs, fish, and sea birds. Populations are sensitive to water quality and algal blooms.
Similar Species
Calico Scallop (Argopecten gibbus), which is more convex and typically has more numerous, narrower ribs with mottled brownish patterns rather than solid color blocks.
Beach Finding Tips
Look along shallow bay beaches, near seagrass beds, or after storms at low tide. Walking the wrack line where light shells wash ashore is the best method.