Broad-ribbed Cardita (also known as the Broad-ribbed Venus)
Phylum: Mollusca; Class: Bivalvia; Order: Carditida; Family: Carditidae; Genus: Carditamera; Species: C. floridana · Carditidae (The Carditas or False Cockles) · Bivalve (clams/two-shelled); single valve shown (left valve); shape is trapezoidal-ovate
Species
Carditamera floridana
Shell Type
Bivalve (clams/two-shelled); single valve shown (left valve); shape is trapezoidal-ovate
Family
Carditidae (The Carditas or False Cockles)
Size
Approximately 0.75 to 1 inch (19-25mm). Standard adult range for this species is 0.5 to 1.5 inches.
Color & Pattern
Base color is off-white to creamy beige with distinct brownish-purple or reddish-brown spots/bars arranged in radial patterns along the ribs. The pattern is natural but slightly weathered by the surf.
Rarity
Very Common; a frequent find on South Carolina beaches like Myrtle Beach.
Habitat
Shallow marine environments, specifically sandy or muddy bottoms, seagrass beds, and rubble areas. Often attached by a byssus to rocks or shells in the intertidal or shallow subtidal zones.
Geographic Range
Western Atlantic: North Carolina to Florida, the Gulf of Mexico, and the Caribbean. Very common in the Southeast United States.
Description
A robust, thick-walled bivalve featuring strong, elevated radial ribs (typically 15-20) that are crossed by fine growth lines, creating a slightly beaded or 'scaly' texture. The shell is noticeably elongated and trapezoidal, with the beaks (umbos) directed toward the anterior end.
Key Features
Distinguished by its heavy, squared-off radial ribs and the characteristic 'checkerboard' or barred brown spotting atop the ribs. The shell's trapezoidal shape and offset beak are diagnostic.
Collector Value
Low monetary value ($1-$3) due to abundance, but highly desirable for beachcombers and hobbyists due to its pretty patterns and sturdy nature. Matching 'paired' valves (dyads) are more valuable to collectors.
Condition Notes
Good. This is a single valve (common for beach finds). The sculpture remains sharp, and the color patterns are clearly visible, though the edges show slight surf-wear. Collectibility grade: Fine.
Interesting Facts
Unlike many clams that burrow deep in the sand, Carditas often use a byssal thread—similar to a mussel—to anchor themselves to hard surfaces or debris on the ocean floor to prevent being swept away by currents.
Ecological Role
Suspension feeder that filters plankton from the water column. They serve as a food source for gastropods (like drills) and crabs. They are not currently a species of conservation concern.
Similar Species
Arka zebra (Turkey Wing) has a similar shape but different hinge and stripes; Venericardia tridentata is much smaller and more circular.
Beach Finding Tips
Look in the 'shell hash' lines at low tide. They are small and often hide among broken shell fragments. Their weight makes them settle in pockets behind sandbars after a storm.
Notes
Myrtle Beach SC