Coquina Clam (Butterfly Shell, Variable Coquina)
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Donacidae, Genus: Donax, Species: Donax variabilis · Donacidae (Bean Clam family) · Bivalve, single valve, fan/wedge shape
Species
Donax variabilis
Shell Type
Bivalve, single valve, fan/wedge shape
Family
Donacidae (Bean Clam family)
Size
Approximately 1 inch (2.5 cm) in length, which is on the larger end for this species. Adults typically range from 0.5 to 1 inch.
Color & Pattern
Solid off-white or cream coloration, appearing slightly sun-bleached with faint concentric growth lines visible. The natural color variations in this species are vast, ranging from white, yellow, orange, pink, purple, to blue with various rayed patterns, though this particular specimen is a monochromatic light shade.
Rarity
Very Common
Habitat
Intertidal zone of high-energy sandy ocean beaches, inhabiting the surf zone where they rapidly burrow into the sand as waves recede.
Geographic Range
Western Atlantic, extending from Virginia south along the Florida coast and throughout the Gulf of Mexico.
Description
A charming, wedge-shaped bivalve shell with a smooth, porcelain-like exterior marked by subtle concentric growth rings. The posterior end is slightly truncated, and the margins are finely toothed on the inner edges. This is a single intact valve displaying a clean, rounded triangular profile.
Key Features
Wedge or wedge-triangle shape, prominent umbo positioned slightly off-center, smooth exterior with concentric growth lines, and small size. The internal margins are finely crenulated.
Collector Value
Low monetary value due to their extreme abundance, but they are highly prized by casual beachcombers and crafters who use them to make shell jewelry, wind chimes, and decorative art.
Condition Notes
Good condition. It is a single intact valve with minor wear along the ventral margin, typical of beach-worn specimens. No major fractures or boring holes are visible. Collectibility grade is Good.
Interesting Facts
Coquina clams are famous for their dynamic behavior; they use their muscular foot to rapidly burrow back into the sand within seconds when a wave pulls back. They emerge in large groups with incoming waves to feed on suspended plankton.
Ecological Role
Coquina clams serve as a vital food source for numerous shorebirds, fish, and crabs, forming a crucial link in the marine food web of sandy beach ecosystems. They also help filter organic matter from the surf.
Similar Species
Donax fossor (Eastern Little Coquina) and Donax dermistosus, which share a similar wedge shape but differ slightly in geographic distribution and subtle shell proportions.
Beach Finding Tips
Look in the swash zone of sandy ocean beaches just as the waves recede. Watch for tiny bubbles or tiny V-shaped disruptions in the wet sand, which indicate a colony of live clams just beneath the surface.