True clams, in the strict sense, are bivalves with equal shells closed by two adductor muscles, and with a powerful, muscular, foot that they use to burrow themselves in the mud
The word is often applied only to those that are edible, spending most of their lives partially buried in the sand of the ocean floor
Clams live in both salt water and fresh water.
Clam needs to open their valves if they move about, and also to allow their two feeding tubes (siphons) to reach out into the water. Bivalves feed by filter microscopic algae out of the water they live in.
Clams can be found in a variety of sizes ranging from 0.004 of an inch to almost 4 feet as seen in the giant clam
Some clams have life cycles of only one year, while at least one may be over 500 years old
Clams age can be calculated by counting rings on its shell. The growth-increments themselves provide a record of how the animal has varied in its growth-rate from year to year, and that varies according to climate, seawater temperature, and food supply.