Coquina, Wedge Shell, or Bean Clam
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Donacidae, Genus: Donax, Species: variabilis · Donacidae (Wedge Clams or Wedge Shells) · Bivalve (Clam/Two-shelled); Wedge-shaped/Triangular
Species
Donax variabilis (Confidence: 85%)
Shell Type
Bivalve (Clam/Two-shelled); Wedge-shaped/Triangular
Family
Donacidae (Wedge Clams or Wedge Shells)
Size
Approximately 0.5 - 0.75 inches (12-19mm). This is typical for a mature specimen of this species, which generally peaks at 1 inch.
Color & Pattern
Muted grayish-blue to pale green with subtle banding. While known for vibrant patterns (plaids, stripes, yellows), this specimen appears naturally matte or slightly beach-worn, likely highlighting the darker interior pigment showing through.
Rarity
Very Common. Often found by the thousands on southeast U.S. beaches during the summer months.
Habitat
Intertidal zone of high-energy sandy beaches. They live just beneath the surface of the sand, constantly moving with the incoming and outgoing waves.
Geographic Range
Western Atlantic, from Virginia south to Florida, and throughout the Gulf of Mexico to Texas.
Description
A small, sturdy, wedge-shaped bivalve. One end is rounded while the other is more pointed or steeply angled. The surface is relatively smooth with very fine radial ribs that can be felt with a fingernail.
Key Features
Distinctive wedge or 'bean' shape; sharply angled posterior end; small size; fine radial striations on the exterior; often found in paired valves (butterfly shells).
Collector Value
Minimal monetary value due to extreme abundance, though highly prized by 'butterfly' shell crafters and beginning beachcombers for their rainbow-like variety of colors.
Condition Notes
Fair to Good. The shell appears intact but exhibits natural beach wear and potential sun-bleaching. The surface lacks the high gloss of a live-taken specimen, graded as a 'Beach' specimen.
Interesting Facts
Known as 'surf clams,' they are famous for their rapid burrowing ability. They use the energy of the waves to migrate up and down the beach to stay in the wash zone, a behavior known as 'tidal migration.'
Ecological Role
Vital filter feeders that clean the water in the surf zone. They are a primary food source for shorebirds like Sanderlings and for various species of crabs and fish.
Similar Species
Donax fossor (which is smaller and more northern) and Donax texasiana (found specifically in the western Gulf of Mexico).
Beach Finding Tips
Look in the 'wash' area as waves retreat. You will often see them digging back into the sand. To collect empty shells, look at the recent high-tide line where small debris accumulates.