Coquina, Wedge Shell, or Bean Clam
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Donacidae, Genus: Donax, Species: variabilis · Donacidae (Wedge Clam family) · Bivalve (Single valve present); Wedge-shaped or triangular
Species
Donax variabilis (Confidence: 95%)
Shell Type
Bivalve (Single valve present); Wedge-shaped or triangular
Family
Donacidae (Wedge Clam family)
Size
Approximately 15mm-20mm in length. This is a mature size, as the species typically ranges from 10mm to 25mm.
Color & Pattern
Soft pastel pink to light apricot base color with faint concentric growth lines. The surface has a natural glossy sheen, though it appears slightly dulled by wave action. No distinct dark rays are visible on this specific specimen, which is common in solid-colored variants.
Rarity
Very Common. These are often the most numerous shells found on Atlantic and Gulf Coast sandy beaches, sometimes appearing in the thousands.
Habitat
Intertidal zone of high-energy sandy beaches. These animals live in the 'swash zone' where waves break and recede, constantly migrating up and down the beach with the tide.
Geographic Range
Western Atlantic, from Virginia south to Florida and throughout the Gulf of Mexico to Texas and Mexico.
Description
A small, sturdy, wedge-shaped bivalve. The shell is characterized by its unequal sides—the posterior end is short and steeply angled, while the anterior end is longer and more rounded. The exterior is relatively smooth with very fine radial hints and concentric growth rings. This specimen shows a lovely monochromatic pastel hue, a hallmark of the species' famous variability.
Key Features
Triangular/wedge shape; posterior side is shorter than the anterior; smooth glossy surface; interior margins usually have fine crenulations (teeth-like ridges) which distinguish Donax from other small clams.
Collector Value
Minimal monetary value ($0.10 - $0.50), but high aesthetic value for 'craft collectors.' They are most desirable when found in large assortments of different colors (purples, yellows, stripes) or as matched 'butterfly' pairs.
Condition Notes
Good condition. It is a single valve (not a paired 'butterfly'). The edges appear slightly worn by surf action, and the periostracum is gone, but the natural pink pigmentation is well-preserved. Collectibility Grade: Fine.
Interesting Facts
Coquinas are famous for their 'dancing' behavior; they use a powerful foot to quickly re-bury themselves after each wave. Historically, they were used to make 'Coquina broth.' In Florida, the sedimentary rock 'Coquina' (made of compressed shells) was used to build the Castillo de San Marcos because it could absorb cannon fire without shattering.
Ecological Role
Vital filter feeders that bridge the gap between microscopic plankton and larger shore predators like crabs, shorebirds (Sanderlings), and fish (Pompano). They are excellent bio-indicators of beach health.
Similar Species
Donax fossor (which is smaller and usually lacks the vivid colors) and Galatea species (found in different regions).
Beach Finding Tips
Look in the 'wash line' as waves recede. To find live ones, look for small bubbles or disturbances in the saturated sand just after a wave pulls back. Sifting the top inch of sand with a mesh tray is the most effective method.