California Bean Clam (also known as the Wedge Shell or Coquina Clam)
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Donacidae, Genus: Donax, Species: Donax gouldii · Donacidae (Wedge Clam or Bean Clam family) · Bivalve (Single valve present); Shape: Wedge-shaped or triangular
Species
Donax gouldii (Confidence Level: 95%)
Shell Type
Bivalve (Single valve present); Shape: Wedge-shaped or triangular
Family
Donacidae (Wedge Clam or Bean Clam family)
Size
Approximately 0.5 to 0.75 inches (12-19mm). This is a typical adult size for this species, which rarely exceeds 1 inch.
Color & Pattern
Base color is a creamy off-white to pale tan with subtle brownish concentric growth lines and faint radiating rays. The shell exhibits a glassy, polished texture. The interior would typically be white, occasionally with purple or yellow staining toward the hinge.
Rarity
Very Common. These shells are frequently found in massive wash-ups on Southern California beaches, including Coronado.
Habitat
Exposed sandy beaches in the intertidal surf zone. They live buried just beneath the surface of the sand where waves break.
Geographic Range
Eastern Pacific coastline, ranging from Santa Cruz, California, south to southern Baja California, Mexico.
Description
A small, sturdy, wedge-shaped bivalve with a smooth, glossy exterior. The anterior end is rounded while the posterior end is shorter and steeply angled, giving it its characteristic bean or wedge shape. The valves are thick for their small size to withstand the heavy pounding of Pacific surf.
Key Features
Distinctive asymmetrical wedge shape (posterior side steeper), glossy finish, concentric growth rings, and a tight-fitting hinge. In Donax gouldii, the exterior is often smoother than its Atlantic relative, Donax variabilis.
Collector Value
Minimal monetary value (less than $1) due to abundance. However, they are highly desirable for 'memory jars' and local Californian collections because of their variety of color forms and association with iconic beaches like Coronado.
Condition Notes
The specimen is a single valve in 'Good' condition. It shows minor beach wear (slight blurring of growth lines) and has lost its periostracum, but the shape and color remain diagnostic. No predator drill holes are visible.
Interesting Facts
Bean clams are famous for 'population explosions' where millions appear on a single beach for a season and then vanish for years. They are 'surf surfers,' using their muscular foot and the movement of the tide to migrate up and down the beach to stay in the saturated wash zone.
Ecological Role
Primary consumer and filter feeder, cleaning the water near the shore. They serve as a vital food source for shorebirds like Sanderlings and Willets, as well as surf fish like Corvina and Corbina.
Similar Species
Donax variabilis (Coquina- Atlantic cousin) which is more colorful; Tivela stultorum (Pismo Clam) which is much larger and thicker as an adult.
Beach Finding Tips
Look at the 'swash line' (the furthest point waves reach) during a receding tide. On Coronado Beach, look for tiny 'V' shapes in the sand as a wave retreats; these are the clams' siphons. Heavy concentrations of empty valves often accumulate in tide pools or depressions in the sand after high surf.
Notes
Coronado beach