McDonald's Happy Meal web site confirms that the October 2015 kids' meal theme will be based on the current film Hotel Transylvania 2 (not The Nightmare Before Christmas, which was released back in in 1993).
There are differences in the shell textures of oysters and clams. The shell of a clam is smooth and shiny while an oyster has a rough outer shell. Both the organisms take in water through the shells but the filtering procedure is different. Oysters produce pearls which are in much demand but clams do not.
Thirty years ago, the Pacific rock oyster was introduced to Europe to boost stocks. It is cheaper than native oysters and is usually available year-round. It grows quickly as our summer temperatures rarely tempt it to spawn, so a rock oyster can reach palatable size in two years (compared with four for a native).