The phylum Mollusca includes snails, clams, chitons, slugs, limpets, octopi, and squid. As mollusks develop from a fertilized egg to an adult, most pass through a larval stage called the trocophore. The trocophore is a ciliated, free-swimming stage. Mollusks also have a radula or file-like organ for feeding, a mantle that may secrete a shell, and a muscular foot for locomotion. Clams are marine mollusks with two valves or shells. Like all mollusks, a clam has a mantle which surrounds its soft body. It also has a muscular foot which enables the clam to burrow itself in mud or sand. The soft tissue above the foot is called the visceral mass. Bend the left valve back so it lies flat in the tray. Run your fingers along the outside and the inside of the left valve and compare the texture of the two surfaces.

Examine the inner dorsal edges of both valves near the umbo and locate the toothlike projections. Close the valves & notice how the toothlike projections interlock.

Locate the muscle \"scars\" on the inner surface of the left valve. The adductor muscles were attached here to hold the clam closed. Identify the mantle, the tissue that lines both valves & covers the soft body of the clam. Find the mantle cavity, the space inside the mantle.

Locate two openings on the posterior end of the clam. The more ventral opening is the incurrent siphon that carries water into the clam and the more dorsal opening is the excurrent siphon where wastes & water leave. With scissors, carefully cut away the half of the mantle that lined the left valve. After removing this part of the mantle, you can see the gills, respiratory structures.

Observe the muscular foot of the clam, which is ventral to the gills. Note the hatchet shape of the foot used to burrow into mud or sand.

Locate the palps, flaplike structures that surround & guide food into the clam\'s mouth. The palps are anterior to the gills & ventral to the anterior adductor muscle. Beneath the palps, find the mouth.

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