Asian Clam, also known as the Corbicula or Asiatic Freshwater Clam
Phylum: Mollusca, Class: Bivalvia, Order: Venerida, Family: Cyrenidae, Genus: Corbicula, Species: Corbicula fluminea · Cyrenidae (Clam family, formerly Corbiculidae) · Bivalve (clams); this is a single valve (one half of the shell). The shape is triangularly ovate or sub-trigonal.
Species
Corbicula fluminea (Confidence: High)
Shell Type
Bivalve (clams); this is a single valve (one half of the shell). The shape is triangularly ovate or sub-trigonal.
Family
Cyrenidae (Clam family, formerly Corbiculidae)
Size
Approximately 15-20mm in width. This is a juvenile to young adult specimen; adults typically reach 25-35mm, though they can reach 50mm in ideal conditions.
Color & Pattern
The exterior features a dark olive to blackish-brown periostracum (outer organic layer). In this specimen, the periostracum is eroded at the umbo (beak) revealing the white calcareous shell underneath. No banding is visible, just uniform dark pigmentation on the outer surface.
Rarity
Very Common. Found in massive quantities in freshwater systems where it has been introduced; often so abundant that thousands of shells line riverbanks and lake shores.
Habitat
Freshwater to slightly brackish environments. Prefers sandy or gravelly substrates in rivers, lakes, and streams with moving water. It is a benthic filter feeder.
Geographic Range
Originally native to Russia, Thailand, Philippines, China, and Korea. Now globally widespread as a highly invasive species across North America, South America, and Europe.
Description
A sturdy, relatively thick small clam with a distinct triangular-oval shape. The most striking sculptural feature is the presence of heavy, evenly spaced concentric ridges or ribs that follow the growth curve of the shell. This specific valve shows the characteristic erosion of the beak area common in specimens from acidic or sandy waters.
Key Features
Heavy concentric ridges (costae) on the exterior; a distinct triangular shape with a central, prominent umbo; dark-colored periostracum which often flakes or erodes to white at the center.
Collector Value
Minimal monetary value. Due to its invasive status and extreme abundance, it is rarely traded among professional collectors, though it is excellent for educational displays about invasive biology.
Condition Notes
Fair to Good. One valve only. The shell shows significant erosion at the umbo and some chipping along the thin posterior edge. This is typical for beach-found freshwater specimens. Collector grade: Utility/Study specimen.
Interesting Facts
Corbicula fluminea is one of the most successful invasive species in the world. It can self-fertilize (hermaphroditic) and release up to 70,000 juveniles a year, allowing a single individual to start an entire colony. In the US, it is famous for clogging water intake pipes for power plants and irrigation systems.
Ecological Role
A prolific filter feeder that competes with native mussels for food and space. By filtering large volumes of water, they can alter the water chemistry and clarity of entire lake systems, often leading to the decline of native biodiversity.
Similar Species
Sphaeriidae (Pea clams) which are much smaller and smoother; Polymesoda caroliniana (Carolina Marsh Clam) which is larger and lacks the heavy, even ridges.
Beach Finding Tips
Look along the high-water mark of freshwater riverbanks, especially after a storm or a drop in water level. They are often found in the drift line mixed with small pebbles and aquatic debris.
Notes