The labeling of the the types of materials found under 741.5 is an ongoing debate between fans, authors and illustrators. Just Google "the difference between comics, graphic novels and manga". The resulting opinions are more than I thought. Debates go on endlessly regarding plot arcs, length, chapters, volumes and series to discern differences. Overall, though most agree that "Comic" is the original term from which all other names (be they revered or despised).
From my experience in libraries, the terms in the title post are regarded as follows:
- Comic Book: Magazine-like bound series material
- Graphic Novel: More sturdily bound than a comic book due to length. Usually a contained story, but can also be series
- Manga: Japanese-created comics and novels, very popular in Western culture.
I suggest a couple of sources for reviewing or choosing relevant materials:
- Good Comics for Kids - School Library Journal's collaborative blog on suggested materials for students
- No Flying, No Tights - A graphic novel review website
And if you are just a self-proclaimed history of comic nerd, see this blog by an aspiring comics librarian: 741.5 and then some.