Calico Scallop (also known as the Placid Scallop)
Phylum: Mollusca, Class: Bivalvia, Order: Pectinida, Family: Pectinidae, Genus: Argopecten, Species: Argopecten gibbus · Pectinidae (Scallop family) · Bivalve (two-shelled), whole shell, fan-shaped with radiating ribs
Species
Argopecten gibbus
Shell Type
Bivalve (two-shelled), whole shell, fan-shaped with radiating ribs
Family
Pectinidae (Scallop family)
Size
Approximately 2 to 3 inches in width, which is average for this species. Adults typically range from 1.5 to 3 inches.
Color & Pattern
Pale creamy white to light beige base coloration with subtle hints of pinkish undertones near the umbo. The surface shows fine concentric growth lines intersecting with numerous radial ribs, creating a delicate reticulated pattern. The coloration appears natural but somewhat faded or sun-bleached compared to living specimens which often feature mottled reddish-brown or purple calico patterns.
Rarity
Common
Habitat
Found in shallow marine waters, typically from the intertidal zone down to depths of about 150 feet. They prefer sandy or shell-gravel substrates, often inhabiting offshore sand flats and seagrass beds.
Geographic Range
Western Atlantic Ocean, ranging from North Carolina south through the Gulf of Mexico, Florida, the Bahamas, and the Caribbean Sea.
Description
This is a classic fan-shaped bivalve shell featuring a prominent, slightly asymmetrical umbo (beak) at the hinge. The exterior displays a finely textured grid-like sculpture formed by numerous radiating ribs crossed by delicate concentric growth rings. The margins are subtly undulating to match the ribbing structure, giving it a classic scalloped edge. The overall appearance is clean, elegant, and sturdy.
Key Features
Nearly equilateral fan shape with a slightly inflated valve, distinct symmetrical ears (auricles) at the hinge line, and numerous fine, evenly spaced radial ribs that create a finely textured, almost checkered surface under magnification.
Collector Value
Low to Moderate. While widely collected and very popular among beachcombers and crafters, they are abundant in their native range and typically hold nominal monetary value, though exceptional color morphs are prized.
Condition Notes
The shell is in Good to Fine condition. It is intact with no major fractures or structural breaks. The exterior shows some minor weathering and sun-bleaching typical of beach-collected specimens, but the delicate radial and concentric sculpture remains crisp and well-defined.
Interesting Facts
Unlike many bivalves that burrow or remain stationary, calico scallops are capable of swimming short distances by rapidly clapping their valves together to expel water. They also possess dozens of simple blue eyes along the mantle edge that can detect light and movement.
Ecological Role
Calico scallops are important filter feeders, helping to maintain water clarity by consuming phytoplankton. They serve as a crucial food source for various marine predators including fish, crabs, and sea stars. Populations can experience massive natural fluctuations from year to year.
Similar Species
Atlantic Bay Scallop (Argopecten irradians), which tends to have fewer, coarser ribs (usually 17-22) compared to the Calico Scallop which typically features more numerous, finer ribs (often 18-26).
Beach Finding Tips
Look for them along Atlantic and Gulf coast beaches, particularly in Florida, right after storm events or high tide lines. Piles of shell drift often accumulate in the upper intertidal zone where whole valves can be sifted out.