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 word oyster is used as a common name for a number of different families of saltwater clams, bivalve molluscs that live in marine or brackish habitats. In some species the valves are highly calcified, and many are somewhat irregular in shape. Many, but not all, oysters are in the superfamily Ostreoidea.