Coquina Clam (also known as Butterfly Shell, Coquina, or Wedge Shell)
Phylum: Mollusca > Class: Bivalvia > Subclass: Heterodonta > Order: Cardiida > Superfamily: Tellinoidea > Family: Donacidae > Genus: Donax > Species: Donax variabilis · Donacidae (Wedge Clam / Coquina family) · Bivalve (single valve shown). Wedge-shaped / triangular profile.
Species
Donax variabilis (Confidence: Very High)
Shell Type
Bivalve (single valve shown). Wedge-shaped / triangular profile.
Family
Donacidae (Wedge Clam / Coquina family)
Size
Approximately 0.75 inches (19 mm) in length, fitting easily on a palm. Adults typically range between 0.5 to 1 inch (12 to 25 mm).
Color & Pattern
Soft yellowish-cream to pale yellowish-tan base, featuring distinct concentric ray bands in subtle greyish-lavender tones following the growth lines near the umbo and mid-shell.
Rarity
Very Common. Found in massive numbers along Atlantic surf zones.
Habitat
Intertidal surf zones along exposed sandy ocean beaches. They burrow rapidly into coarse to medium sand using a muscular foot as waves wash over them.
Geographic Range
Western Atlantic from Long Island, New York south through Florida, the Gulf of Mexico, and down to the Caribbean. Very common along the Carolinas including Oak Island, NC.
Description
A classic wedge-shaped bivalve valve with a smooth, polished exterior marked by subtle concentric growth lines and delicate radial striae. The shell is noticeably elongated at one end and sharply sloped at the posterior end.
Key Features
Distinctive asymmetrical wedge/triangular shape, smooth shiny surface, finely serrated inner margin along the valve edge, and characteristic variable color banding.
Collector Value
Low monetary value (under $1 for single shells) due to abundance, but highly popular among beachcombers and crafters for their incredible range of bright color variations.
Condition Notes
Good to Fine condition. Whole single valve with intact margins, excellent original coloration, and minimal erosion.
Interesting Facts
Coquinas often wash ashore in double valves held together by an elastic ligament, unfolding like butterfly wings—hence the nickname 'Butterfly Shell'. They are dynamic burrowers that ride waves up and down the tide line.
Ecological Role
Crucial primary consumers in surf ecosystems, filtering plankton and organic detritus while serving as a vital food source for shorebirds, fish, and crabs.
Similar Species
Donax fossor (Fossor Coquina, generally smaller and found further north) and Donax denticulatus (Caribbean Wedge Clam, featuring stronger radial sculpture).
Beach Finding Tips
Look in the wet sand where waves recede in the swash zone. Watch for tiny bubbles or sudden burrowers right after a wave washes over the sand.
Notes
Oak Island NC