Method of Dissecting a Clam

Before Dissection

• Before dissecting a clam, place it in a dissecting tray and look it over. Orient yourself to its exterior. At the point where the two valves hinge there is a hump called the umbo. The side of the clam along which the umbo lies is the dorsal or hinge side. The opposite side of the clam is the ventral or opening side. The surface of the valves between the dorsal and ventral sides are the laterals. The umbo is closer to one end of the valves than the other end. The closer end is the anterior end. The opposite end is the posterior end. Concentric growth lines radiate from the umbo. The hinge, a ligament made of inter-meshing teeth, connects the valves.

Opening the Valves

• In order to view the interior of the clam, one valve must be removed. This can be accomplished in a couple of ways. Place the clam dorsal side down and insert the tip of a screwdriver between the ventral edges of the valves. Work it in .25 inch to .5 inch and then turn the blade to pry the edges apart. Alternatively, place the clam ventral side down and use a scalpel to cut through the hinge ligament, which will reveal an opening into which can be placed the end of a pair of medium-sized scissors. Work them in about .25 inch. Slowly turn the scissors to pry apart the valves. With either method, a scalpel can then be used to locate and cut through the larger posterior and smaller anterior adductor muscles, which hold the valves closed. Cut the muscles as close to the left valve (the valve that will be toward you if you hold the clam dorsal side up, posterior to the right) as possible. Be careful to cut only the muscle. Use small scissors to completely sever any remaining adhesions and remove the left valve.

Removing the Mantle

• The mantle lines each valve and produces calcium carbonate, which forms the hard outer shell. Use dissecting scissors to cut away the mantle that overlays the gills, foot, respiratory organs and palps, the flap-like organs that guide and sort food. Lift the palps to discover the mouth. Lift the foot and the large visceral mass above it and note that the clam has gills, palps and mantle on either side, arranged symmetrically.

Dissecting the Gills

• Cut out a small section of gill with dissecting scissors. Place it on a microscope slide and observe an uncut edge under the microscope. Notice the small hair-like structures called cilia that are used to move food from the gills to the palps.

Dissecting the Visceral Mass

• Inside the visceral mass, a large muscle-like structure above the foot, lie the digestive gland, crystalline style and gonads. Carefully cut through the upper layer of the mass with scissors and a probe to reveal them. Or use a scalpel to cut the muscle at the top of the foot, then carefully peel it back. You can also approach the area by cutting through the mouth and esophagus. The gonads, or reproductive organs, are spongy and yellow. The digestive gland is greenish and pulpy. The crystalline style, which rotates to release digestive enzymes, sits in its own sac. It looks like a small glass worm. Probe the digestive gland to find it. Further dissection with probe and scissors should allow you to trace the digestive system from the mouth to the style sac, and from there to the intestine, which travels through the pericardium to the anus, above the posterior adductor muscle.