The Ocean Quahog (Arctica islandica), also known by a number of different common names including Icelandic cyprine, mahogany clam, mahogany quahog, black quahog, and black clam, is a species of edible clam, a marine bivalve mollusk in the family Arcticidae. This species is native to the North Atlantic Ocean. Like other clam species, the ocean quahog is a filter feeder. Feeding activity appears regulated by light levels, which can be used as a proxy for food availability. This means that at the northern extreme of the distribution, feeding is concentrated during 8 months of the year, while during the rest of the year the clams only feed for a few days a month.
The typical ocean quahog resembles the quahog (Mercenaria mercenaria), but the shell of the ocean quahog is rounder, the periostracum is usually black, and on the interior of the shell, the pallial line has no indentation, or sinus. They grow to sizes exceeding 50 millimeters or 2 inches shell height. An individual specimen was reported to have lived 507 years, making it the longest-lived non-colonial metazoan whose age was accurately known.