Broad-ribbed Cardita (also known as the Broad-ribbed Clam)
Phylum: Mollusca, Class: Bivalvia, Order: Carditida, Family: Carditidae, Genus: Carditamera, Species: C. floridana · Carditidae (Cardita family) · Bivalve (two-shelled). These specimens are single valves with an elongated oval to sub-trapezoidal shape.
Species
Carditamera floridana (Confidence Level: 95%)
Shell Type
Bivalve (two-shelled). These specimens are single valves with an elongated oval to sub-trapezoidal shape.
Family
Carditidae (Cardita family)
Size
The larger specimen is approximately 15-18mm (0.6-0.7 inches); the smaller is roughly 5mm. Mature adults typically reach 25-40mm (1-1.5 inches).
Color & Pattern
Creamy white to light beige base. The exterior features heavy radial ribs decorated with brownish-purple or reddish-orange spots and bars. The interior is typically porcellaneous white, sometimes with a hint of the exterior spotting visible through the shell wall.
Rarity
Very Common. These are frequent finds on Florida Gulf Coast beaches, often appearing in large numbers in shell drift.
Habitat
Shallow marine environments, specifically intertidal to shallow subtidal zones. They prefer sandy or muddy bottoms and are often found nestled in seagrass beds (Thalassia).
Geographic Range
Western Atlantic, specifically from Florida and the Gulf of Mexico through the Caribbean to the West Indies.
Description
A sturdy, thick-walled bivalve characterized by 15-20 strong, rounded radial ribs. The shell is noticeably inequilateral, with the beaks (umbones) positioned toward the anterior end. The ribs are crossed by fine growth lines, giving the colorful spots a modular, beaded appearance. The hinge is robust with distinct cardinal teeth.
Key Features
Distinguished by its heavy radiating ribs, purple-brown spotting on the ribs, and its elongated shape compared to more circular cockles or scallops.
Collector Value
Low monetary value ($0.50-$2.00) due to abundance, but high educational value for beginners. 'Gem' quality paired valves with deep purple markings are the most desirable for collectors.
Condition Notes
Fair to Fine. The larger shell shows significant 'beach wear' (abrasion on the ribs and whitening due to sunlight), while the smaller one retains more vivid color. Both are single valves; find as a 'double' (live-paired) shell is rarer.
Interesting Facts
Unlike many clams that burrow deep, Cardita species have a small byssus (thread-like attachment) when young to tether themselves to substrate, similar to mussels. They are often called 'Bird Wing Clams' by children due to their silhouette.
Ecological Role
Suspension feeders that filter plankton from the water column. They serve as a food source for gastropods like drills and for various shorebirds.
Similar Species
Carditamera gracilis (thinner ribs) and various members of the Arcidae (Ark clams), which have a much straighter hinge line and many more small teeth.
Beach Finding Tips
Look in the 'wrack line' or amongst shell piles after a high tide. They are particularly abundant on the west coast of Florida (Sanibel, Captiva, and Marco Island).