California Bean Clam (also known as the Coquina Clam of the West)
Phylum: Mollusca; Class: Bivalvia; Order: Cardiida; Family: Donacidae; Genus: Donax; Species: D. gouldii · Donacidae (Wedge Shell or Bean Clam family) · Bivalve (single valve present in image); Wedge-shaped/Triangular
Species
Donax gouldii
Shell Type
Bivalve (single valve present in image); Wedge-shaped/Triangular
Family
Donacidae (Wedge Shell or Bean Clam family)
Size
Approximately 12-18mm in length. This is a mature size for this species, which rarely exceeds 25mm (1 inch).
Color & Pattern
Highly variable. This specimen shows a creamy-white base with concentric lavender and tan banding. The interior of this species is typically glossy white, often stained with purple or yellow near the margins.
Rarity
Very Common. These shells can often be found by the thousands on California beaches during 'bloom' years.
Habitat
Sandy intertidal zones of high-energy beaches. They live just beneath the surface of the sand in the wash zone where waves break.
Geographic Range
Eastern Pacific: From Santa Cruz, California, south to southern Baja California, Mexico. Extremely common on Southern California beaches like Coronado.
Description
A small, sturdy, wedge-shaped bivalve with a smooth, glossy surface. The anterior end is elongated and rounded, while the posterior end is shorter and steeply angled, giving it a distinct 'bean' or 'wedge' profile. The valves are equal in size and fit tightly together to protect the animal from the crushing force of surf-tossed sand.
Key Features
Heavy, thick valves for its small size; distinct wedge shape where one side is much shorter and flatter than the other; fine concentric growth lines; incredibly varied color patterns unique to each individual.
Collector Value
Minimal monetary value ($0.50-$1.00) due to abundance, but high aesthetic value for 'beach jar' collectors. The fun for collectors lies in finding the vast array of different color morphs (yellow, purple, white, striped).
Condition Notes
The specimen appears to be a single 'dead-taken' valve in Fine condition. It retains good color and luster, though the edges show slight smoothing from surf action. No visible predator drill holes.
Interesting Facts
The California Bean Clam is famous for its massive population fluctuations; one year a beach may have millions, and the next year almost none. They are 'surf-surfers,' using their muscular foot to pop out of the sand and ride the incoming or outgoing tide to maintain their position in the ideal wash zone.
Ecological Role
They are vital filter feeders that clarify coastal waters. They serve as a primary food source for shorebirds (like Willets and Sanderlings), surf fish, and crabs. They are sensitive to beach pollution and oil spills.
Similar Species
Donax californicus (California Wedge Clam), which is thinner, more elongated, and typically found in calmer bays rather than open surf beaches.
Beach Finding Tips
Look in the 'wash zone' as the tide is receding. You will often see them as small bumps in the wet sand. On beaches like Coronado, look for areas where the receding wave leaves a tiny 'V' shaped wake in the sand—this is often the siphon of a live Bean Clam.
Notes
Coronado beach