Dosinia (Commonly known as the Disk Shell or Concentric Dosinia)
Phylum: Mollusca, Class: Bivalvia, Order: Venerida, Family: Veneridae, Genus: Dosinia, Species: Dosinia concentrica · Veneridae (Venus Clam family) · Bivalve; single valve (left); circular/disc-shaped.
Species
Dosinia concentrica
Shell Type
Bivalve; single valve (left); circular/disc-shaped.
Family
Veneridae (Venus Clam family)
Size
Approximately 1.5 to 2 inches (38-50mm). This is typical for a mature specimen of this species, which usually tops out around 3 inches.
Color & Pattern
Off-white to creamy yellowish exterior. The shell exhibits a uniform coloration with no distinct dark patterns or bands, typical of weathered beach specimens from North Carolina. The interior is likely white and porcelain-like.
Rarity
Common; frequently found on the beaches of the Carolinas especially after storms or high tides.
Habitat
Inhabits shallow subtidal waters, typically buried in sandy or muddy substrates from just offshore to approximately 50 meters deep.
Geographic Range
Western Atlantic, ranging from North Carolina down through the Caribbean and Gulf of Mexico to Brazil.
Description
A beautifully symmetrical, disc-like bivalve shell characterized by its remarkably circular outline and compressed, flat profile. The surface is adorned with numerous, fine, closely spaced concentric ridges that are evenly distributed from the umbo (beak) to the outer margin. The shell is sturdy and has a porcelain-like texture, often appearing polished when fresh.
Key Features
Nearly perfect circular shape; flattened (compressed) profile; fine, regular concentric ridges; small, forward-curving beak (umbo); lack of radial ribs.
Collector Value
Minimal monetary value ($1-$5) but high aesthetic value for enthusiasts due to its geometric perfection. It is a 'staple' shell for East Coast collectors.
Condition Notes
Good condition. The concentric ridges are well-defined and not excessively worn. There is some slight beach-wear on the beak, and it is a single valve rather than a paired specimen. Color is slightly sun-bleachable but retains natural cream tones.
Interesting Facts
The genus name 'Dosinia' is derived from 'Dosina', a name assigned by Adanson in 1757 based on a Senegalese vernacular name. These clams are filter feeders that use a long siphon to breathe and eat while remaining buried safely beneath the sand.
Ecological Role
Benthic filter feeder that helps clear the water column of organic particles. They serve as a food source for bottom-dwelling fish, rays, and predatory gastropods like whelks.
Similar Species
Dosinia discus (Elegant Dosinia), which is very similar but usually has even finer, more numerous concentric ridges (over 20 per inch vs. roughly 15-20 for D. concentrica).
Beach Finding Tips
Look along the wrack line (the line of debris left by high tide) at Holden Beach. They are most easily found after a period of strong onshore winds or during low tide following a storm.
Notes
Holden Beach, NC