California Donax, Wedge Shell, Bean Clam
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Donacidae, Genus: Donax, Species: D. californicus · Donacidae (Wedge Clam or Bean Clam family) · Bivalve (single valve fragment), Wedge-shaped/Triangular
Species
Donax californicus (Confidence Level: 95%)
Shell Type
Bivalve (single valve fragment), Wedge-shaped/Triangular
Family
Donacidae (Wedge Clam or Bean Clam family)
Size
Approximately 12-18mm in length. This is right in the typical adult range for the species (up to 25mm).
Color & Pattern
Base color of creamy off-white with subtle yellowish-tan radial bands. Features faint growth lines. Interior is typically white or tinged with purple/yellow (not visible in this orientation).
Rarity
Common beach find on San Diego area beaches like Coronado, though often found as single valves rather than paired.
Habitat
Inhabits the intertidal zone of sandy beaches, specifically found burrowed just beneath the surface in the wave-wash zone or in sheltered bays and estuaries.
Geographic Range
Eastern Pacific: Southern California (Santa Barbara) down to Baja California, Mexico and the Gulf of California.
Description
An attractively wedge-shaped bivalve with a smooth, glossy surface. The posterior end is distinctly shortened and steeply angled, giving it a 'beaked' or triangular appearance. The valves are thin but sturdy for their size.
Key Features
Distinctly asymmetrical wedge shape; smooth texture with very fine radial striations; posterior end is shorter and blunter than the anterior end.
Collector Value
Low monetary value ($0-$1) due to abundance. However, they are highly desirable for coastal crafts and as representative specimens for regional biodiversity collections.
Condition Notes
Fair to Good. The specimen is a single valve rather than a complete living pair. Shows minor edge wear and sun-bleaching typical of beach-drift shells. No significant predator boring holes visible.
Interesting Facts
These clams are 'surf-riders'—they use their muscular foot to pop out of the sand and ride the incoming or outgoing tide to maintain their position in the ideal wave-wash zone for filter feeding.
Ecological Role
Critical primary consumer in sandy beach ecosystems; they filter plankton from the water and serve as a major food source for shorebirds like Sanderlings and various surf fish.
Similar Species
Donax gouldii (Gould's Bean Clam) which is more plump and rounded; Donax fossor of the East Coast which is larger and more elongated.
Beach Finding Tips
Look in the 'surf line' just as the tide is receding. In San Diego/Coronado, they often appear in massive colonies called 'beds' where thousands can be seen briefly as the water pulls back.
Notes
Coronado beach