Oysters and clams are pretty similar and take in water through their shells but they filter the water different.
Oysters also produce pearls while clams do not produce any pearls.
Another difference between oysters and clams is that oysters have a rough outer shell to them while clams have a shiny and smooth shell.
Both clams and oysters are related and belong to the same mollusk family, and have lots of similarities but the above is what is different about them.