Coquina Shell (also known as Variable Wedge Shell or Donax Clam)
Phylum: Mollusca; Class: Bivalvia; Order: Cardiida; Family: Donacidae; Genus: Donax; Species: Donax variabilis · Donacidae (Wedge shell or Bean clam family) · Bivalve (single valve shown). Wedge-shaped or triangular.
Species
Donax variabilis
Shell Type
Bivalve (single valve shown). Wedge-shaped or triangular.
Family
Donacidae (Wedge shell or Bean clam family)
Size
Approximately 15-20mm (0.6-0.8 inches). This is a mature adult for the species, which typically tops out at 25mm.
Color & Pattern
Displays a warm base color of tan and peach with concentric bands of mahogany purple and rust brown. In sunlight, these shells often show a slight radial shimmer. The interior (unseen) is usually polished and matches the exterior bands.
Rarity
Very Common. These are the most abundant shells found on North Carolina beaches, often appearing in the thousands during outgoing tides.
Habitat
Marine; Intertidal zone. Found in the high-energy wash of sandy beaches (the swash zone). They are active burrowers in wet sand.
Geographic Range
Western Atlantic from Virginia to Florida and throughout the Gulf of Mexico (Holden Beach, NC is a classic locality).
Description
A small, sturdy, wedge-shaped bivalve with a smooth, almost glossy surface. The shell is characterized by its inequilateral shape, where the posterior end is short and rounded while the anterior end is elongated. It features fine, barely visible radial striae and distinct concentric growth rings.
Key Features
Triangular wedge shape; highly variable color patterns; fine serrations along the inner margin of the valves (crenulations); distinct asymmetrical hinge placement.
Collector Value
Minimal monetary value ($0.05 - $0.25) due to extreme abundance. However, they are highly desired by hobbyists for 'memory jars' and craft work due to their incredible variety of colors.
Condition Notes
Good to Fine. The shell retains strong natural pigmentation and lacks major chips. There is minor surface weathering (chalkiness) near the umbo (beak) typical of beach-collected specimens.
Interesting Facts
The living animal is a master of 'surfing.' They use the waves to move up and down the beach with the tide to stay in the saturated sand. They were historically used by coastal settlers to make 'Coquina broth,' a thin clam soup.
Ecological Role
Vital filter feeders that serve as a primary food source for shorebirds (like Sanderlings), crabs (like Ghost Crabs), and certain fish (like Pompano). They are excellent indicators of beach health.
Similar Species
Donax fossor (which is smaller and usually less colorful) and Donax parvulus (which lives just outside the surf line and is more elongated).
Beach Finding Tips
Look in the 'swash zone' where waves are receding. You can often see them quickly digging back into the sand. To find empty shells, look for small 'wrack lines' of shell hash at the high tide mark.
Notes
Holden Beach, NC