subgenre 
noun
A subdivision of a genre of literature, music, film, etc.There was also the breaking down of the music into subgenre after sub-genre, to the point at which it became somehow incomprehensible....
- One of the most tried and true of the movie subgenres is the heist film.
- His first foray into feature film-making is successful, although Ice Age is not a standout in the still-small subgenre of computer animated films.