Coquina, Variable Wedge Shell, Butterfly Shell
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Donacidae, Genus: Donax, Species: variabilis · Donacidae (Wedge Clam family) · Bivalve (Single Valve). Shape is wedge-shaped/triangular.
Species
Donax variabilis
Shell Type
Bivalve (Single Valve). Shape is wedge-shaped/triangular.
Family
Donacidae (Wedge Clam family)
Size
Approximately 15-20mm in length. This is an adult specimen; the species typically ranges from 10mm to 25mm.
Color & Pattern
Highly variable. This specimen shows concentric bands of mauve, gray, and cream. The surface is smooth with faint radial striae. Interior would likely be white or purple-tinged.
Rarity
Very Common. These are often found in massive colonies of thousands.
Habitat
Found in the intertidal zone of sandy beaches, specifically at the wash line where waves break.
Geographic Range
Western Atlantic: From Virginia south to Florida, Gulf of Mexico, and the Caribbean.
Description
A small, elegant wedge-shaped bivalve with a smooth, glossy surface. Its posterior end is short and steeply angled, while the anterior end is longer and more rounded. The shell is sturdy for its size and known for its vibrant, rainbow-like diverse color patterns.
Key Features
Wedge-shaped profile, crenulated (finely notched) inner margins on the interior lip, and distinct concentric color banding.
Collector Value
Low monetary value but High aesthetic value. Collectors often seek to find a 'butterfly pair' (both valves still hinged) in unusual colors or patterns.
Condition Notes
Good condition. It is a single valve rather than a paired 'butterfly.' The margins are intact, and the color is well-preserved, not heavily beach-worn or sun-bleached.
Interesting Facts
The living animals are 'surf sailors' that migrate up and down the beach with the tide to stay in the wash zone. They are often used to make a flavored broth known as Coquina broth.
Ecological Role
Primary consumer/Filter feeder. They are a vital food source for shorebirds, crabs, and fish (like Pompano). They are not currently protected.
Similar Species
Donax fossor (smaller, less colorful) and Donax roemeri. Easily distinguished from juvenile Mercenaria by its distinct wedge shape.
Beach Finding Tips
Look at the water's edge just as a wave recedes. You will see them quickly burrowing back into the sand. Sifting the top inch of wet sand near the wash line is most effective.