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.
The European Flat has a large, straight shell with fine ridges, whereas the Pacific Oysters are smaller with wavy casings. Kumamotos are also smaller, and the shell is rounder and pale, which is similar to the Olympias, though this one has a smoother shell with a bit of iridescent coloring.