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Hard Clam

M. campechiensis; M. mercenaria


Southern Quahog (Mercenaria campechiensis)
Northern Quahog (Mercenaria mercenaria)


  • Clams are bivalves, or molluscs that have two shells joined by an elastic hinge
  • Exterior shells are dirty gray or whitish colored
  • Northen clams may have brown zig-zag patterns; juvenile northern clams have raised ridges
  • Interior of shell usually white, although northern clam may have purple shading along the outer edges
  • Two adductor muscles are used to close the shell
  • Two siphons are used to draw in or expel sea water
  • Hatchet-shaped foot is used to burrow into sand or mud

Similar Species

Marsh clams (Rangia cuneata) are similar in appearance and are the more common clam in the very low salinity portion of the estuary.


Southern Quahog: up to 6.5 inches in length and 3.5 inches thick across the hinge 

Northern Quahog: up to 5 inches in length and 5 inches thick across hinge


Typically found in soft sediments located from the high-tide line to as deep as 118 feet (36 meters) of water; common in sand or sand-mud bottoms and tolerates a medium salinity up to full strength seawater. Southern clams will also be found in seagrass beds and northern clams can also be found in oyster reefs.


Growth is most rapid in spring and fall. Southern quahogs grow fastest, from a little more than a half-inch to nearly three inches in diameter in two years. Northern quahogs reach three inches in diameter in about three years. Typically, growth is greater in deeper areas with submerged aquatic vegetation.

Feeds on very small plants and decaying organic matter that are suspended in sea water.


Hard clams are protandrous hermaphrodites, meaning most begin life as males but often change to females. However, the clams can both revert back to males as well as exist as hermaphrodites. In Florida, spawning occurs in spring and fall when water temperatures reach about 73 degrees Fahrenheit. A female may spawn several times each year, producing millions of eggs. The two species hybridize and form individuals with intermediate characteristics.

Additional Information

May live up to 22 years.

Recreational regulations 

Hard clams research