Coquina, Wedge Shell, Butterfly Shell
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Donacidae, Genus: Donax, Species: Donax variabilis · Donacidae (Wedge shell family) · Bivalve (single valve petal-shaped fragment); Wedge-shaped or triangular.
Species
Donax variabilis (Confidence: 95%)
Shell Type
Bivalve (single valve petal-shaped fragment); Wedge-shaped or triangular.
Family
Donacidae (Wedge shell family)
Size
Approximately 12-15mm in length. This is a standard adult size; the species typically ranges from 10mm to 25mm.
Color & Pattern
Uniform pastel mauve or tan exterior. Interior likely possesses a deeper purple or pink hue. The color appears slightly weathered but natural, lacking the high gloss of a fresh specimen but retaining biological pigment.
Rarity
Very Common
Habitat
Marine; high-energy intertidal surfe zones. These animals live just beneath the sand surface in the wash of the waves.
Geographic Range
Western Atlantic, ranging from Virginia to Florida and throughout the Gulf of Mexico.
Description
A small, sturdy, wedge-shaped bivalve with a smooth, slightly polished surface. The shell is characterized by its inequilateral shape, where the posterior end is shorter and steeply angled compared to the elongated anterior. When found in pairs, they often open up like butterfly wings.
Key Features
Triangular/wedge shape, smooth exterior with very fine radial strikes, and an interior margin that is finely serrated (crenulated).
Collector Value
Minimal monetary value due to extreme abundance. They are highly valued by hobbyists for 'beach jars' or craft work due to their incredible range of rainbow colors.
Condition Notes
Fair to Good. One valve of the pair is missing. The edges appear slightly rounded from surf wear, and the luster is matte, suggesting it has spent time tumbling in the swash zone.
Interesting Facts
Coquinas are famous for 'surfing'; they use their muscular foot to pop out of the sand and ride waves up and down the beach to stay in the ideal feeding zone. Historically, they were harvested to make 'Coquina broth' in Florida.
Ecological Role
Vital filter feeders that serve as a primary food source for shorebirds like Sanderlings and various species of crabs and fish.
Similar Species
Donax fossor (Small Wedge Shell), which is typically smaller and more northern, and Donax roemeri.
Beach Finding Tips
Look at the water's edge as the tide recedes. You will see thousands of tiny 'bubbles' or small holes in the wet sand where they are burrowing back down after a wave passes.