Coquina, Butterfly Shell, or Donax
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Donacidae, Genus: Donax, Species: variabilis · Donacidae (Wedge Shell or Coquina family) · Bivalve (Single valve present); Wedge-shaped / Triangular
Species
Donax variabilis (Confidence level: 85% based on shape and hue)
Shell Type
Bivalve (Single valve present); Wedge-shaped / Triangular
Family
Donacidae (Wedge Shell or Coquina family)
Size
Approximately 0.5 to 0.75 inches; this is a mature size as the species rarely exceeds 1 inch.
Color & Pattern
Soft pastel mauve/pink with subtle concentric growth lines. The color appears natural but slightly matte, typical of a beach-worn specimen. Many specimens exhibit radial rays of darker color, though this one seems mostly solid.
Rarity
Very Common; these are among the most abundant shells found on Atlantic sandy beaches.
Habitat
Intertidal zone of sandy ocean beaches; they live just under the sand surface in the wash zone where waves break.
Geographic Range
Western Atlantic, specifically from Virginia through the Gulf of Mexico and into the Caribbean.
Description
A small, sturdy, wedge-shaped bivalve with a smooth, glossy interior. The exterior features fine concentric ridges and a steep posterior slope. When both valves are connected and open, they resemble butterfly wings, giving them their common nickname.
Key Features
Distinctive wedge/triangular shape with the 'beak' or umbo located toward the posterior end. The shell is heavier and more durable than other small clams like tellins.
Collector Value
Low monetary value ($0.10 - $0.50) but high sentimental value for beachcombers. They are best displayed in large groups or 'memory jars' due to their incredible color variety.
Condition Notes
Fair to Good. It is a single valve (separated from its pair). The edges appear slightly rounded by wave action, and the surface has lost some of its high-gloss lustre, indicating it was on the beach for some time before being found.
Interesting Facts
Coquinas are famous for their 'dancing' behavior; they use a powerful muscular foot to quickly re-bury themselves into the sand after each wave passes. Historically, they were used to make 'Coquina broth,' a traditional coastal Florida dish.
Ecological Role
Primary consumer and filter feeder; they serve as a vital food source for shorebirds, crabs, and fish like Florida Pompano. They are indicators of a healthy, oxygenated beach ecosystem.
Similar Species
Donax fossor (which is smaller and more northern) and various species of Tellin (which are flatter and more fragile).
Beach Finding Tips
Look at the 'wash' line as the tide recedes. You can often see them active in the wet sand, or find large deposits of empty valves in the shell hash near the high-tide line.