Encased in a shell, clams are bivalves, meaning their shell consists of two parts, known as valves. The two halves of the shell are joined together by a section called the umbo, which is the oldest part of the shell, from which it originates and grows outward. The clam's strong adductor muscles, located on either side of the shell, allow it to close tightly. To open, hinge ligaments near the umbo stretch once the adductor muscles relax.
Filtering water for food, clams feed using a siphon that extends outward from their shells. The diet of clams consists of plankton, microscopic organisms that drift through the water. When hungry, a clam extends its double-tubed siphon, accoding to the Department of Natural Resources, and pulls in water which is then filtered by the clam's gills. Next, a mixture of food and mucus is moved to the clam's stomach for digestion and the excess water is released through the other end of the siphon.
Mating is a stationary activity for clams, who must find a way to mingle their cells while buried in sediment. When spring arrives and waters warm, male and female clams engage in broadcast spawning, meaning they release their eggs and sperm into the water, where they meet, fertilize and eventually turn into baby clams. Some clam species can release up to a million eggs at a time and live up to twenty years, giving them innumerable chances to reproduce.
Assisted by muscular tissue, clam shells can grow quickly and slowly at different periods during the creature's life. In order for its shell to expand, the mantle, described as a "thin tissue that adheres to the inner surfaces of the shell," by the Northeast Fisheries Science Center, works with a thick trim of muscular tissue at the mantle's edge create new shell material. Placed at the edge of the shell, it develops and forms rings, which can be counted to determine the clam's age.