Flat Zirfaea or White Dosinia (Common Venus Clam)
Phylum: Mollusca, Class: Bivalvia, Order: Venerida, Family: Veneridae, Genus: Dosinia, Species: Dosinia discus · Veneridae (Venus Clams) · Bivalve; these are single valves (separated halves). Shape is discoidal/circular with a distinct beak (umbo).
Species
Dosinia discus
Shell Type
Bivalve; these are single valves (separated halves). Shape is discoidal/circular with a distinct beak (umbo).
Family
Veneridae (Venus Clams)
Size
The largest specimen is approximately 2.5 to 3 inches in diameter. This is within the average adult range for this species, which can reach up to 4 inches.
Color & Pattern
Pure white to cream/off-white. The surfaces show a faint yellowish tint near the umbo of the largest shell. No distinct spots or bands; the pattern consists entirely of fine, concentric growth lines.
Rarity
Common; these shells are frequently found on Atlantic and Gulf Coast beaches, especially after storms or high tides.
Habitat
Marine; typically found in shallow subtidal waters, often buried in sandy or muddy substrates. They are common in nearshore environments and high-energy surf zones.
Geographic Range
Western Atlantic, ranging from Virginia down to the Florida coast and throughout the Gulf of Mexico to the Bahamas.
Description
A very flat, nearly circular bivalve characterizes by its elegance and symmetry. The shell is remarkably compressed (flat) compared to other Venus clams. The surface is adorned with incredibly fine, closely spaced concentric ridges that look like the grooves of a vinyl record. The beak (umbo) is small and points forward.
Key Features
Distinguished by its exceptionally flat profile, nearly perfect circular outline, and the high density of fine concentric rings. The lunule (the heart-shaped depression near the hinge) is long and narrow.
Collector Value
Common; primarily of decorative or educational value. While beautiful due to their symmetry, they are not high-value items, usually valued between $1-$5 depending on size and perfect condition of the hinge.
Condition Notes
The shells appear to be in 'Fine' to 'Good' condition. They show slight weathering/beach wear on the edges, and the smallest shell on the right has a minor chip on the posterior margin. The white color is natural, though slightly dulled by sand abrasion.
Interesting Facts
Dosinia clams are known for being deep burrowers. Their flat shape allows them to slice through sand with minimal resistance. The genus name is derived from 'Dosina', a name given by Adanson to a similar clam from Senegal.
Ecological Role
Suspension feeders; they filter phytoplankton and organic detritus from the water column. They serve as a food source for gastropods like Moon Snails and various species of rays and sea birds.
Similar Species
Dosinia elegans (Elegant Dosinia) is very similar but is typically more inflated (less flat) and has slightly coarser concentric ridges.
Beach Finding Tips
Look along the high-tide line after a storm. Because they are flat and light, they are often pushed high up onto the sand. They are most common on the sandy beaches of Florida and the Carolinas.