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Hard Clams




Life Cycle


Ark Clams


Soft Shell Clams



 Hard Calm or Northern Quahog

Anatomy                                                             <click on any image to enlarge>

 Clams are bivalves, meaning that they have shells consisting of two halves, or valves.


The valves are joined at the top, and the adductor muscles on each side hold the shell closed. If the adductor muscles are relaxed, the shell is pulled open by ligaments located on each side of the umbo.

The clam's foot is used to dig down into the sand, and a pair of long siphons that extrude from the clam's mantle out the side of the shell reach up to the water above (only the exit points for the siphons are shown).

Note: this image is colored to differentiate internal organs and are not the actual colors of the clam.

Clams are filter feeders. Water and food particles (and anything else that may be floating by) are drawn in through the incurrent siphon where tiny, hair-like cilia move the water to the gills.  Food is caught in mucus produced by the gills. The gills also draw oxygen from the water flow. 

From there, the cilia move the particles along food grooves toward the labial palps, where they are sorted. The labial palps secrete a mucus that entangles suspended food and nutrient particles within the water to produce a ball of food and mucus called a bolus.  Afterwards, cilia on the palps direct the bolus into the mouth.

Other particles—such as silt or excess phytoplankton—are dropped onto the surface of the mantle, where the clam eventually gets rid of them in mucous-coated balls.

Food is processed by the digestive system which includes the stomach, intestines, rectum and anus.      <click here> or on the image for more details

The excurrent siphon carries away the water, disregarded (non-food) particles and waste.

Most bivalves are filter feeders, trapping suspended food particles as water passes through their gills. Two groups, the nuculoids and cryptodonts, actively feed on organic material within the sediment and are thus true deposit feeders. Taxodont dentition is characteristic of deposit feeders.

More about the shell:

The hard calm has its soft tissue surrounded by a shell consisting  of two halves (valves).

When the clam is active and feeding, the shell continues to grow.

The shell consists of calcium carbonate and is held together by a though, pliable ligament at the top (dorsal) section of the animal called the hinge.

The hinge allows for the opening and closing of the shell. In close proximity to the hinge is the umbo commonly known as the "beak"   The umbo is the oldest section of the shell with subsequent shell growth radiating out from it.                     <click on image to enlarge>


The mantle is a soft, retractable organ attached to both sections of the inside of a clam's shell and is directly responsible for creating and growing the clam's shell.

The mantle processes the calcium deposits that it has stored over weeks or months. The clam opens its shell and extends its mantle to the edges of both sides. The mantle releases the glue-like calcium compounds along the edges of the shell.


Clams survive by getting oxygen and food from the waters of the bay.  As the bay warms up the nutrients become more plentiful.  This includes algae that is the principal food for clams. 

Algae is one form of phytoplankton that clams draw in thought their incurrent siphon.  Green Algae (pictured to the right) are microscopic organisms that utilize the nutrients (mostly Nitrogen) in the bay to synthesize their own food by means of photosynthesis.

Along with food and oxygen, whatever else that is floating in the bay is also drawn in by the calm.

The water is passed through the gills where gas exchange (oxygen for carbon dioxide) occurs. 

The gills also have specialized cells that produce mucus to trap food and non-food particles which are passed to the labial palps and mouth to start the digestive process.

Waste material and undigested food is passed to the rectum and anus.  The anus opens into a chamber that leads directly into the excurrent siphon.


 The Assateague Naturalist -