Coquina Shell, Butterfly Shell, Wedge Shell
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Donacidae, Genus: Donax, Species: Donax variabilis · Donacidae (Wedge Clam family) · Bivalve (Single valve/half shell); Wedge-shaped/Triangular
Species
Donax variabilis (Confidence: 95%)
Shell Type
Bivalve (Single valve/half shell); Wedge-shaped/Triangular
Family
Donacidae (Wedge Clam family)
Size
Approximately 0.75 inches (19mm). This is typical for a mature adult; species range is 0.5 to 1 inch.
Color & Pattern
Pale cream base with concentric grayish-purple banding and a distinctive dark violet or brown border along the outer posterior edge. Features a smooth, glossy finish with subtle radial rays visible near the margins. The interior is likely a highly polished white or purple.
Rarity
Very Common; ubiquitous on many sandy Atlantic and Gulf beaches.
Habitat
Marine; intertidal surf zones. Found buried shallowly in sandy beaches where the waves break.
Geographic Range
Western Atlantic, specifically from Virginia to the Gulf of Mexico and throughout the Caribbean.
Description
A small, sturdy, wedge-shaped bivalve with a highly polished exterior. The shell is notable for its incredible color variability (polymorphism). This specimen shows a subtle 'pastel' gradient. The shell has an asymmetrical shape with a rounded anterior end and a more sharply angled, truncated posterior end.
Key Features
Distinctive wedge/triangular shape; asymmetrical valves; smooth glossy texture; concentric growth lines; small serrations (crenulations) on the inner margin of the valves.
Collector Value
Minimal monetary value ($0.10 - $0.50) due to abundance. Highly valued by hobbyists for 'beach art' and jewelry due to their array of rainbow colors.
Condition Notes
Good collector condition. The luster is well-preserved, suggesting it was found recently after the animal died. There is very minor chipping on the edges. Grade: Fine.
Interesting Facts
Known as 'Butterfly Shells' because when the two halves open while connected at the hinge, they resemble butterfly wings. They are incredibly fast burrowers, using their foot to re-bury themselves in seconds after being unearthed by a wave.
Ecological Role
Vital filter feeders that process nutrients in the surf zone. They are a primary food source for shorebirds like Sanderlings and various crabs and fish.
Similar Species
Donax fossor (smaller and more northern/temperate) and Donax texasianus (more common in the western Gulf of Mexico; usually less colorful).
Beach Finding Tips
Look at the 'swash zone' as the tide recedes. During low tide, look for tiny holes or bubbles in the wet sand where they are buried just below the surface.