Coquina Clam (Butterfly Bean Clam)
Phylum: Mollusca, Class: Bivalvia, Order: Venerida, Family: Donacidae, Genus: Donax, Species: Donax variabilis · Donacidae (Bean Clam family) · Bivalve, whole shell, triangular fan shape
Species
Donax variabilis
Shell Type
Bivalve, whole shell, triangular fan shape
Family
Donacidae (Bean Clam family)
Size
Approximately 0.75 inches (19 mm) in length, which is average for an adult of this species. Adults typically range from 0.5 to 1 inch.
Color & Pattern
Solid chalky white appearance, likely sun-bleached or worn. Natural specimens of this species are famously polymorphic, exhibiting vibrant rays, bands, and splashes of yellow, orange, pink, purple, blue, and brown. The interior is smooth and matches the exterior white.
Rarity
Very Common
Habitat
Inhabits high-energy sandy intertidal zones of ocean beaches, typically living just beneath the surface in the surf zone where waves break and wash ashore.
Geographic Range
Western Atlantic Ocean, from Virginia south along the Florida coast and throughout the Gulf of Mexico.
Description
A small, sturdy, wedge-shaped to triangular bivalve shell with a pointed umbo and fine concentric growth lines. The ventral margin is slightly curved, and the posterior end is shorter and truncated.
Key Features
Distinctive wedge or triangular profile, inequilateral shape with a short posterior end, and prominent concentric growth lines.
Collector Value
Low monetary value due to extreme abundance, though highly sought after by beachcombers for making shell crafts and colorful mosaic displays.
Condition Notes
Good condition whole single valve. Uniformly white due to weathering and sun-bleaching, with minor wear along the ventral margin but structurally intact.
Interesting Facts
Coquina clams are famous for their remarkable ability to burrow rapidly back into the wet sand using their muscular foot just seconds after a wave recedes, avoiding predators and displacement.
Ecological Role
Serves as a crucial food source for shorebirds, fish, and crabs, and acts as an active filter feeder helping to clear suspended organic matter from surf zone waters.
Similar Species
Donax fossor (Eastern Little Bean Clam), which is generally smaller and found further north; distinguished primarily by subtle differences in shell proportions and hinge teeth.
Beach Finding Tips
Look along the wet swash zone of ocean-facing sandy beaches just as a wave recedes, watching for tiny bubbles or quick movements in the sand where they burrow.