Giant clams (including oysters, scallops, and similar shellfish) are found in shallow water, to a maximum depth of 200 feet. The soft-bodied mollusk lives in a hard, protective shell that it opens for feeding and closes against predators. The upper shell of the giant clam is a light brown (some have white markings), the lower shell is white. The clam has tiny blue eye-spots located near the edge of its shell. These can distinguish between light and shadow and detect movement, but cannot estimate size. Special organs near the front of the mantle cavity, where the soft body of the clam sits, detect and analyze chemical traces in the water.
The giant clam is not a direct threat, but can be dangerous if approached incautiously. When threatened or when something tries to reach inside the shell, the shellfish reacts by closing its shell. The clam's adductor muscles, which act as a hinge for the shell, are quite powerful.
The giant clam is not usually found in large numbers, though rumors persist of large beds. Some undersea races, such as tritons, tend beds where domesticated giant clams or oysters are grown. Unconfirmed rumors suggest the possibility of intelligent or even psionic clam and oyster colonies.
The most important predator of giant clams and oysters are giant starfish and, of course, greedy humans seeking wealth. The inside of the shell is lined with mother-of-pearl, and a few giant mollusks contain a single giant pearl, which might be as large as a fist, but will not be as lustrous as smaller pearls from common pearl oysters.
Note: Giant clams originally appeared in this form in the Monstrous Compendium Annual Volume 4 for the AD&D game from TSR. Their use here is for the purposes of providing context for the campaign only.