Pacific Calico Scallop (also known as the Circular Semicaris or Speckled Scallop)
Phylum: Mollusca, Class: Bivalvia, Order: Pectinida, Family: Pectinidae, Genus: Argopecten, Species: A. ventricosus · Pectinidae (Scallop family) · Bivalve (two-shelled), whole individual valve with slightly damaged auricles/ears, fan-shaped shell morphology
Species
Argopecten ventricosus
Shell Type
Bivalve (two-shelled), whole individual valve with slightly damaged auricles/ears, fan-shaped shell morphology
Family
Pectinidae (Scallop family)
Size
Approximately 1.5 to 2 inches in width and length. This is a medium-sized specimen, typical of adults found along the Pacific coast of North America which generally range from 1 to 2.5 inches.
Color & Pattern
Featuring a mottled or 'calico' pattern with a creamy off-white base heavily overlaid with striking reddish-orange radial streaks and charcoal-grey to purplish patches concentrated near the umbo and outer margins. The coloration is entirely natural and well-preserved, showing good contrast.
Rarity
Common to Uncommon depending on the specific local beach, though whole, brightly colored specimens like this are valued finds for casual beachcombers.
Habitat
Found in shallow subtidal to moderately deep marine waters, typically inhabiting sandy or muddy bottoms, often associated with eelgrass beds and protected bays where they can rest or swim freely.
Geographic Range
Eastern Pacific Ocean, ranging from Point Conception, California, down through the Gulf of California and along the coast of Mexico to Peru, including the waters around San Diego.
Description
An attractive, roughly symmetrical fan-shaped bivalve shell featuring prominent, rounded radial ribs radiating from the umbo. The margins are crenulated, mirroring the external ribs on the interior surface. It possesses two unequal auricles (ears) at the hinge line, characteristic of the scallop family, giving it a classic winged appearance at the apex.
Key Features
Nearly equilateral fan shape, prominent and rounded radial ribs (usually numbering around 20-24), unequal auricles at the hinge with the anterior ear being slightly longer, and the distinctive calico pattern of orange and grey spots on a pale background.
Collector Value
Low to Moderate. While widely available and not exceptionally expensive, colorful specimens from specific localities like San Diego are popular among beginner collectors and for craft use, typically valued at a few dollars.
Condition Notes
Good condition. The exterior pattern and structural ribs are well-preserved with vibrant color. There is minor chipping or wear on the auricles near the hinge line, but the main body of the valve remains intact, making it a pleasant specimen for a starter collection.
Interesting Facts
Unlike most bivalves that burrow or remain sessile, scallops like Argopecten ventricosus are capable of swimming. By rapidly snapping their valves together, they expel water to jet-propel themselves away from predators such as sea stars.
Ecological Role
Scallops serve as an important food source for numerous marine predators including crabs, rays, fish, and sea stars. As filter feeders, they also help clean the water column by consuming microscopic plankton and organic particles.
Similar Species
Equatorial Pacific scallops or Atlantic Calico Scallops (Argopecten gibbus). A. gibbus is found in the Atlantic and Gulf of Mexico, making geographic location the easiest way to differentiate it from the Pacific A. ventricosus.
Beach Finding Tips
Look along sandy beaches near bays, estuaries, or sloughs after winter storms or high tides. Searching the wrack line where shell debris accumulates is often the most productive method.
Notes
San Diego