Pacific Calico Scallop (also known as the Broad-ribbed Scallop)
Phylum: Mollusca, Class: Bivalvia, Order: Pectinida, Family: Pectinidae, Genus: Argopecten, Species: Argopecten ventricosus · Pectinidae (Scallop family) · Bivalve (two-shelled clam), whole single valve, fan shape
Species
Argopecten ventricosus
Shell Type
Bivalve (two-shelled clam), whole single valve, fan shape
Family
Pectinidae (Scallop family)
Size
Approximately 1.5 to 2 inches in diameter, which is typical for a medium-sized adult specimen of this species. Adults normally range from 1.5 to 3 inches.
Color & Pattern
Off-white to cream base coloration with notable sun-bleaching. A distinct brownish-orange organic mark or residue is present in the interior cavity. The exterior typically features mottled patterns of brown, orange, or reddish spots, though much of the original pigmentation appears faded on this particular weathered specimen.
Rarity
Common, frequently encountered by beachcombers along the Southern California and Baja California coasts.
Habitat
Shallow subtidal zones to moderate depths, typically found on sandy bottoms, mudflats, and among seagrass beds where they can lie unattached or use their byssal threads temporarily when young.
Geographic Range
Eastern Pacific Ocean, ranging from southern California and the Gulf of California down to Peru, highly consistent with a finding in San Diego.
Description
An attractive, roughly symmetrical fan-shaped bivalve shell featuring rounded ribs radiating outward from the umbo. The margins are crenulated to match the external ribs, and the hinge area displays classic unequal auricles (ears) typical of the scallop family. The interior is smooth with a glossy porcelain-like finish.
Key Features
Equivalved or slightly inequivalved fan shape, prominent radiating ribs (usually around 20-26), asymmetrical wings at the hinge line, and a single central adductor muscle scar visible on the interior.
Collector Value
Low commercial value, typically collected as a casual beach souvenir rather than a high-end specimen. Common beach-worn valves have little monetary value, while pristine live-taken specimens with full color patterns are valued slightly higher by beginner hobbyists.
Condition Notes
Fair condition. The specimen is a single weathered valve showing signs of sun-bleaching, minor edge wear, and an unusual brownish residue or stain in the interior cavity. No major structural fractures, graded as Good for a beach find.
Interesting Facts
Scallops are unique among bivalves because they are capable of swimming by rapidly clapping their valves together to expel water, and they possess dozens of simple blue eyes along the edge of their mantle that can detect light and shadow.
Ecological Role
Scallops serve as an important food source for marine predators including fish, rays, sea stars, and octopuses. As filter feeders, they help clarify coastal waters by consuming microscopic phytoplankton and organic particles.
Similar Species
Other Pacific scallop species such as the Leafy Hornmouth or Rock Scallop (Crassadoma gigantea), but Argopecten ventricosus is readily distinguished by its more symmetrical fan shape and smoother, more numerous radial ribs.
Beach Finding Tips
Look along sandy Southern California beaches, particularly after winter storms or high tides. Scallop valves wash up easily due to their lightweight, convex shape acting like tiny cups in the surf.
Notes
San Diego