Bean Clam (often referred to as the California Donax or Wedge Shell)
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Donacidae, Genus: Donax, Species: Donax gouldii · Donacidae (Wedge Clam or Bean Clam family) · Bivalve (two-shelled mollusk); this specimen is a single valve. Shape is wedge-shaped/triangular.
Species
Donax gouldii (Confidence: 95%)
Shell Type
Bivalve (two-shelled mollusk); this specimen is a single valve. Shape is wedge-shaped/triangular.
Family
Donacidae (Wedge Clam or Bean Clam family)
Size
Approximately 0.75 inches (18mm). Adults typically range from 0.5 to 1 inch. This is a mature specimen.
Color & Pattern
Smooth, creamy white to yellowish base with faint concentric growth lines. Many specimens exhibit radial bands of purple or brown (though this one is lighter/sun-bleached). The interior usually shows a glossy porcelain-like finish.
Rarity
Very Common. They are one of the most abundant shells found on Southern California sandy beaches.
Habitat
Intertidal zone on sandy beaches. They are famous for migrating up and down the beach with the tide in the 'wash' zone. Marine environment.
Geographic Range
Eastern Pacific coast, specifically from Santa Cruz, California, down to Southern Baja California, Mexico. Very common on San Diego area beaches like Coronado.
Description
A small, sturdy, wedge-shaped bivalve. The shell is thicker than it appears, designed to withstand the heavy crashing surf of the Pacific. It features a rounded anterior end and a steeply angled posterior end, giving it its characteristic 'bean' or 'wedge' look. The surface is relatively smooth with very fine radial striae and concentric growth rings.
Key Features
Distinctive wedge shape; heavy, solid feel for its small size; serrated inner margins (visible upon close inspection of the interior edge); and an offset umbo (beak) toward the posterior end.
Collector Value
Low monetary value due to extreme abundance, but highly desirable for craft enthusiasts and beginning collectors. Value is primarily sentimental or used in bulk for biological study/display.
Condition Notes
Good condition. The shell appears beach-worn but intact. The exterior has lost some of its vibrant 'fresh' luster due to sun exposure and tumbling in the sand, but the structure is solid with no major chips.
Interesting Facts
Donax gouldii populations are known for massive 'blooms' where millions can appear on a single stretch of beach, followed by years of scarcity. They use a powerful muscular foot to burrow rapidly back into the sand after each wave passes. Locally, they were historically used to make clam broth.
Ecological Role
Filter feeders that help clear particulate matter from the surf zone. They are a vital food source for shorebirds like Sanderlings and Willets, as well as surf fish and rays.
Similar Species
Donax californicus (California Donax) which is more elongated and thinner, and Donax variabilis (Coquina) found on the Atlantic coast.
Beach Finding Tips
Look at the 'wash' line as the tide recedes on sandy beaches like Coronado or Silver Strand. They are often found in the very shallow water or just under the surface of wet sand. After a storm, they can be found in small drifts of 'shell hash.'
Notes
Coronado beach