 During the first seasons opening credits, for some reason neither The  Professor (Russell Johnson) nor Mary Ann (Dawn Wells) received an onscreen  billing, nor were they referred to in the theme song. They are just  referred to as "... and the rest."  For season two they were added at the  request of Bob Denver, who played "Gilligan" and thought it was stupid to  leave out the two actors just to shorten the song by a few notes.