Coquina Clam (Butterfly Shell, Bean Clam)
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Donacidae, Genus: Donax, Species: Donax variabilis · Donacidae (Coquina family) · Bivalve (two-shelled clam), whole single valve, wedge-shaped or triangular
Species
Donax variabilis
Shell Type
Bivalve (two-shelled clam), whole single valve, wedge-shaped or triangular
Family
Donacidae (Coquina family)
Size
Approximately 0.75 inches long, which is a standard adult size. Adults typically range from 0.5 to 1 inch.
Color & Pattern
Off-white to pale cream base with subtle concentric growth lines and faint yellowish radial banding. The natural coloration is severely faded due to beach wear, revealing the white calcium carbonate inner layer.
Rarity
Very Common, frequently found washed ashore in large numbers on sandy beaches.
Habitat
High-energy sandy intertidal zones of ocean beaches, typically found burrowing rapidly in the swash zone where waves break and recede.
Geographic Range
Western Atlantic Ocean, from Virginia southwards along the Florida coast and throughout the Gulf of Mexico.
Description
A small, wedge-shaped bivalve shell featuring a smooth yet distinctly lined texture with fine concentric growth rings. The margin is slightly angled, and the overall form is adapted to withstand heavy surf action by anchoring firmly in shifting sands.
Key Features
Wedge shape, asymmetrical triangular outline, prominent concentric growth lines, and a thickened hinge area designed for rapid burrowing.
Collector Value
Low commercial value due to high abundance, but highly prized by casual beachcombers who collect them to make colorful shell crafts and jewelry.
Condition Notes
Worn and sun-bleached condition (Fair collectibility grade), missing its vibrant natural array of purples, yellows, and oranges, with smooth edges from wave tumbling.
Interesting Facts
Coquina clams are famous for their ability to rapidly burrow back into the sand using a muscular foot before the next wave washes them away. They are a crucial food source for shorebirds and fish.
Ecological Role
Serves as an essential link in the marine food web by filtering microscopic plankton from the water column and providing sustenance for numerous fish and shorebird species.
Similar Species
Donax denticulatus (Caribbean coquina), which is distinguished by fine tooth-like serrations along the shell margin.
Beach Finding Tips
Look in the wet sand right at the edge of the receding surf on high-energy sandy ocean beaches, particularly during low tide.