The Southern Quahog, Mercenaria campechiensis (Gmelin, 1791), is a large member of the Venus Clam family Veneridae that may grow to be more than 6 inches in size. This local species was originally covered in my column of August 22, 2014. I decided to write again about this magnificent clam after examining and taking a photo of the hinge of a very large specimen. The hinge represents the main connection between the valves, or halves, of the shell of a bivalve mollusk. It has a number of strongly interlocking “teeth,” which in some cases may resemble the cogs in a gear wheel. The hinge prevents the clam’s predators from sliding the shell valves past each other to reach the soft parts of the animal inside. It achieves that while still allowing the animal to slightly open the shell (by relaxing the adductor muscles that, when contracted, keep the shell shut) for feeding and breathing.The photo on the right was taken looking “up” on the inner part of the shell “beak;” it shows the distinctive hinge teeth as well as the distinct “scars” that represent former areas of contact between the clam’s muscles and its shell.
The photos show Southern Quahog, Mercenaria campechiensis, left valve on top, right valve on bottom. The detail on the right shows the interlocking hinge teeth, with the left valve on bottom. Photos by José H. Leal.