The Southern Quahog, Mercenaria campechiensis (Gmelin, 1791), is a large member of the Venus Clam family Veneridae that may grow to be 6 inches in size. The Southern Quahog is often found in the shallow, sandy-mud flats of the local bays and protected areas, where it is one of the main food sources for large Horse Conchs and Lightning Whelks. The species is very similar to the Northern Quahog, Mercenaria mercenaria, with which it is known to hybridize in controlled aquaculture settings. (The Northern Quahog is also the one of the main ingredients of New England clam dishes.) As it happens with many species of mollusks, the shell of young Southern Quahogs (two images on the right in illustration) differs consistently from those of adults: the young shell has a color pattern of zig-zagish brown lines, and exhibits a different shape, more rectangular than the adult.
The Southern Quahog, two valves of the adult shell on left, and same for young shell on right. The adult measures 4.5 inches, the young a little more than one inch. Photos by José H. Leal.