Coquina Clam or Butterfly Clam (also known as Donax shell)
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Donacidae, Genus: Donax, Species: Donax variabilis · Donacidae (Bean Clam or Wedge Shell family) · Bivalve (two-shelled clam), whole single valve shown, triangular or wedge-shaped
Species
Donax variabilis
Shell Type
Bivalve (two-shelled clam), whole single valve shown, triangular or wedge-shaped
Family
Donacidae (Bean Clam or Wedge Shell family)
Size
Approximately 1 inch in length, which is on the larger end for this species. Adults typically range from 0.5 to 1 inch.
Color & Pattern
Off-white to pale grayish base with subtle concentric growth rings. This particular specimen appears sun-bleached, but living or fresh specimens of this species are famously polychromatic, displaying vibrant shades of purple, yellow, orange, pink, blue, and brown with radial rays.
Rarity
Very Common
Habitat
Found in high-energy sandy intertidal zones of ocean beaches, typically burrowing rapidly into the wet sand in the swash zone where waves break.
Geographic Range
Western Atlantic Ocean, specifically along the coastlines of the southeastern United States from Virginia down to Florida, and throughout the Gulf of Mexico.
Description
A charming, solid, wedge-shaped bivalve with prominent concentric growth lines and a slightly asymmetrical triangular outline. The shell features a pointed beak (umbo) and a smooth interior margin, designed perfectly to withstand turbulent surf environments.
Key Features
Wedge shape, pronounced concentric growth ridges, asymmetrical posterior end, and robust, thick shell walls relative to its small size.
Collector Value
Low commercial value due to high abundance, but highly cherished by beachcombers and crafters who use them to create intricate shell art, jewelry, and wind chimes.
Condition Notes
Good condition whole single valve. It is sun-bleached with a uniform off-white color, lacking the natural glossy luster and bright polymorphic color bands of a live-collected specimen. No major structural fractures visible.
Interesting Facts
Coquina clams are famous for their synchronized mass migrations up and down the beach with the tides, using their muscular foot to burrow out of the sand as waves recede and re-burrowing instantly as the next wave arrives.
Ecological Role
They serve as a crucial food source for numerous shorebirds, fish, and crabs, and act as natural filter feeders helping to maintain coastal water quality.
Similar Species
Other members of the Donax genus, such as Donax denticulatus found in the Caribbean, which tends to have more prominent tooth-like margins.
Beach Finding Tips
Look in the wet swash zone of sandy ocean beaches just as a wave recedes. Watch for tiny bubbling holes or sudden movements in the sand where they are rapidly burrowing.