Broad-Ribbed Carditid (also known as the Broad-Ribbed Mussel-Cockle)
Phylum: Mollusca, Class: Bivalvia, Order: Carditellida, Family: Carditidae, Genus: Carditamera, Species: C. floridana · Carditidae (Carditid/Little Cockle family) · Bivalve (Two-shelled); Single valve (left) present in the image. Shape is trapezoidal to sub-ovate with a prominent beak.
Species
Carditamera floridana
Shell Type
Bivalve (Two-shelled); Single valve (left) present in the image. Shape is trapezoidal to sub-ovate with a prominent beak.
Family
Carditidae (Carditid/Little Cockle family)
Size
Approximately 0.75 to 1.25 inches (19-32mm). This appears to be a mature adult specimen, as the species typically reaches 1 to 1.5 inches.
Color & Pattern
Base color is a creamy grey-white with distinct brownish-purple or mahogany-colored spots and bars across the ribs. The interior (not fully visible) is typically white with a hint of purple near the posterior end. The pattern follows the raised radial ribs.
Rarity
Very Common. This is a staple find for beachcombers along the Florida coastline and the Gulf of Mexico.
Habitat
Found in shallow marine environments, particularly in sandy or muddy bottoms, seagrass beds (Thalassia), and near oyster reefs. They are common in the intertidal zone and shallow subtidal waters.
Geographic Range
Western Atlantic, specifically from North Carolina south through Florida, the Gulf of Mexico, and throughout the Caribbean to the West Indies.
Description
A robust, thick-walled bivalve with an elongated, somewhat rectangular or 'mussel-like' shape. The shell features approximately 15 to 20 strong, coarse radial ribs that are crossed by fine growth lines, creating a slightly beaded or scale-like texture. The beak (umbo) is positioned near the anterior end and is strongly curved forward.
Key Features
Heavy radial ribbing, the specific 'beaded' texture of the ribs, the offset umbo (beak) toward one side, and the characteristic rectangular-ovate silhouette.
Collector Value
Minimal monetary value ($1-$3) due to its abundance. However, it is highly valued by amateur collectors for its beautiful geometric symmetry and as a representative species of sub-tropical seagrass ecosystems.
Condition Notes
The specimen is in Good to Fine condition. It shows some natural beach wear (slight smoothing of the ribs at the umbo), but remains intact. The diagnostic color patterns are still visible, which often bleach to pure white in older beach-worn shells.
Interesting Facts
Unlike many clams that burrow deep, Carditamera floridana often lives attached to submerged objects or within seagrass by means of a small byssus (thread-like anchors), similar to how a mussel attaches to rocks. This species was once a food source for indigenous coastal peoples.
Ecological Role
They act as filter feeders, processing plankton and organic detritus from the water column, thereby improving water clarity. They provide a food source for crabs, gastropods (like drills), and certain fish.
Similar Species
Often confused with the 'Three-toothed Cardita' (Carditamera tridentata), which is smaller and more rounded, or the 'Ponderous Ark' (Noetia ponderosa), which is much larger and heart-shaped in cross-section.
Beach Finding Tips
Look in the 'wrack line' (debris left by high tide) among seagrass fragments. They are most easily found after storms or high winds that detach them from their seagrass anchors. Best found on low energy beaches in the Gulf of Mexico.