The mantle of a clam is within the interior of the shell. It lines the underside of both shell valves and contains the animal's internal organs. The outside surface of the mantle is made up of mantle lobes, and the interior is called the mantle cavity.
The mantle lobes are paired organs, each lining the inside of their respective half of the shell. They serve as a soft covering for the organs of the clam. They also secrete the calcium carbonate that makes up the clam's shell. The mantle is made up of three folds: the outermost one makes and repairs the shell, the middle fold contains sensory cells, and the innermost fold regulates water flow into and out of the shell.