They can be found near the edge or in the depth of the water. Differently from other animals, clams are treated as containers, which means that it is possible to store items inside them, no matter the size. More than that, clams are safe containers, which means that any items stored will remain, they will not disappear.
When opening a clam, it may have a pearl inside it. Pearls come in two varieties: Flawed Pearl and the normal Pearl. There is also a third and more valuable type, the Flawless Pearl, but unlike the other two, it will not appear inside clams.
Clams can serve as safe containers to low level characters. There are clams right in the front of the Imperial City Sewers exit, in the water.