Variable Coquina, Butterfly Shell, Wedge Shell
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Donacidae, Genus: Donax, Species: Donax variabilis · Donacidae (Wedge Clam family) · Bivalve (Right valve only, wedge-shaped)
Species
Donax variabilis (Confidence: 95%)
Shell Type
Bivalve (Right valve only, wedge-shaped)
Family
Donacidae (Wedge Clam family)
Size
Approximately 15-20mm in length; typical for a mature adult in this species which ranges from 10-25mm.
Color & Pattern
Glossy exterior featuring a dark chocolate brown to purple-black posterior band against a cream base. Distinct white radial rays and concentric growth lines are visible. The colors appear natural and well-preserved.
Rarity
Very Common
Habitat
Intertidal zone of sandy beaches, specifically the wash zone or 'surf' zone where waves break. Marine environment.
Geographic Range
Western Atlantic, ranging from Virginia to Florida and throughout the Gulf of Mexico to Texas.
Description
A small, sturdy, wedge-shaped bivalve with a smooth, highly polished surface. The shell is inequilateral with a shortened, steeply angled posterior end and a longer, rounded anterior end. It features fine radial striae and distinct concentric growth rings.
Key Features
Wedge-like profile, sharply angled posterior, highly variable color patterns, and a finely serrated inner ventral margin (crenulations).
Collector Value
Low monetary value ($0.10 - $1.00) but high aesthetic value. They are popular for 'butterfly' displays where both valves are opened flat to resemble wings.
Condition Notes
Good to Fine condition. The shell maintains its natural luster and 'sun-ray' patterns. No visible predator drill holes, though as a single valve, it is separated from its pair.
Interesting Facts
These clams are famous for 'surfing' the tides; they use their muscular foot to pop out of the sand and ride waves up and down the beach to stay in the wash zone for filter feeding.
Ecological Role
Vital nutrient recycler and a primary food source for shorebirds (like Sanderlings), crabs, and surf fish. They are indicators of beach ecosystem health.
Similar Species
Donax fossor (thinner, more northern range) and Donax texasiana (smaller, found in Western Gulf).
Beach Finding Tips
Look in the 'swash zone' just as a wave recedes. You will often see them quickly burrowing back into the wet sand. They are most abundant on high-energy sandy beaches.