Caribbean Coquina, Painted Donax, Sunrayed Donax
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Donacidae, Genus: Donax, Species: variabilis · Donacidae (Wedge clam or Donax family) · Bivalve (Two-shelled); Single valve (left) present in image; Wedge-shaped/Triangular
Species
Donax variabilis (Confidence: 95%)
Shell Type
Bivalve (Two-shelled); Single valve (left) present in image; Wedge-shaped/Triangular
Family
Donacidae (Wedge clam or Donax family)
Size
Approximately 12-15mm (0.5 inches). This is a mature adult for this species, which typically maxes out at around 20mm.
Color & Pattern
Glossy white base with subtle radial banding. Shows a characteristic lavender-purple hue near the posterior/hinge area. The exterior has a smooth, polished finish with very fine concentric growth lines and faint radial striations.
Rarity
Very Common. These are among the most numerous shells found on sandy Atlantic and Caribbean beaches.
Habitat
Marine; Intertidal zone, specifically the 'swash zone' where waves break on sandy beaches. They stay buried just beneath the surface in the wet sand.
Geographic Range
Western Atlantic and Caribbean Sea, ranging from Virginia down through Florida, the Gulf of Mexico, Cancun (Yucatán Peninsula), and the Caribbean islands.
Description
An elegant, small bivalve with a distinctively wedge-shaped profile. The shell is sturdy for its size, featuring a highly polished surface that resists the abrasive action of shifting sand. One end is rounded while the other (posterior) is more abruptly truncated or angled. The interior is usually as colorful and glossy as the exterior.
Key Features
Wedge-like triangular shape; highly polished exterior; crenulated (finely toothed) inner margins of the shell valves; distinct radiating color bands or solid hues ranging from white and yellow to purple.
Collector Value
Minimal monetary value (less than $1) due to extreme abundance. However, they are highly desirable for 'color series' collectors who enjoy finding every possible color variation from a single beach.
Condition Notes
Good to Fine. The shell retains its natural luster and color. The margins look relatively sharp, though being an individual valve (beach-worn) rather than a paired living specimen, it is a standard 'beach find' grade.
Interesting Facts
Coquinas are 'surf-riding' specialists; they use their muscular foot to quickly re-bury themselves every time a wave moves them. Mass migrations of these clams can sometimes color entire stretches of beach. Historically, they were used to make 'Coquina broth' and even used as a building material (coquina stone) in Florida.
Ecological Role
Critical primary consumer in the beach ecosystem; they filter-feed on microscopic algae and are a vital food source for shorebirds (like Sanderlings), crabs, and surf fish.
Similar Species
Donax denticulatus (Common Caribbean Donax) - can be distinguished by more pronounced radial ribs; Donax fossor - which is usually smaller and less colorful.
Beach Finding Tips
Look in the 'wash line' as the tide is receding. In Cancun, they are easily found by digging slightly into the wet sand right where the waves lick the shore; you will often see them 'pop' out and try to burrow back down.
Notes
Cancun