Ocean Quahog (also known as Mahogany Clam, Black Clam, or Iceland Quahog)
Phylum: Mollusca, Class: Bivalvia, Order: Venerida, Family: Arcticidae, Genus: Arctica, Species: A. islandica · Arcticidae (Ocean Quahog family) · Bivalve (two-shelled clam), whole shell valve, fan-shaped to rounded oval
Species
Arctica islandica
Shell Type
Bivalve (two-shelled clam), whole shell valve, fan-shaped to rounded oval
Family
Arcticidae (Ocean Quahog family)
Size
Approximately 3.5 to 4 inches in length, which is a mature and very typical size for this species. Adults commonly range from 2 to 4 inches, though they can occasionally grow larger.
Color & Pattern
The exterior shown is heavily sun-bleached to a chalky off-white with faint remnants of a brownish-orange periostracum near the umbo (beak). In living or fresh specimens, the shell is covered by a thick, dark brown to black velvety periostracum, which conceals a chalky white underlying calcareous layer.
Rarity
Very Common. This is a very abundant commercial species regularly washed up on northern New England beaches, particularly after storms.
Habitat
Found in cold, shallow to deep subtidal marine waters, typically burrowing in fine sand, muddy sand, or soft mud substrates on the continental shelf.
Geographic Range
Boreal to Arctic waters of the North Atlantic Ocean, ranging from the Arctic circle down to Cape Hatteras in North America, and along the European coasts from Iceland and Norway to the Bay of Biscay.
Description
A sturdy, thick-walled, rounded-oval bivalve shell with prominent concentric growth lines marking the animal's decades-long life stages. The umbo is moderately prominent and incurved. The exterior surface displays coarse concentric ridges following the shell margins. While fresh specimens are dark and unassuming, weathered beach specimens like this one turn a bright, chalky white.
Key Features
Solid, heavy, rounded-oval shape; lack of a pallial sinus on the internal muscle scars (distinguishing it from similar hard-shell clams); prominent concentric growth rings; and a strong internal hinge plate.
Collector Value
Low commercial or monetary value because they are exceptionally common. However, they are highly valued by marine biologists and educational collectors due to their legendary longevity and ecological significance.
Condition Notes
Fair to Good condition for a beach-collected single valve. The shell is structurally intact with a clear, well-defined shape and visible growth lines, but it is heavily sun-bleached and weathered with loss of the original dark periostracum and minor surface abrasion near the umbo.
Interesting Facts
Arctica islandica holds the record for being one of the longest-lived animals on Earth. Individuals routinely live for over 200 years, and a famous specimen nicknamed 'Ming' was scientifically determined to be a staggering 507 years old, making it older than the Ming Dynasty when it died.
Ecological Role
A vital benthic filter feeder that processes large amounts of organic particulate matter from the water column. Their long lifespan and sensitive growth rings make them crucial bioarchives for studying historical ocean climate change and marine pollution.
Similar Species
Northern Quahog or Hard Clam (Mercenaria mercenaria), which features a distinct purple interior margin and a prominent pallial sinus inside, whereas the Ocean Quahog lacks the purple coloration and has an entire mantle line without a sinus.
Beach Finding Tips
Look along northern New England sandy beaches, especially at Popham Beach, Maine, after a heavy offshore storm or high tide line siftings, where heavy shells are deposited among seaweed and debris.
Notes
Popham beach Maine