20 classes. But classes aren't like in DD at all. There are almost only patterns of costs for different habilities. Character are created by spending points in these habilities, cheaper or more expensive depending of the class. Some classes also give bonuses/level to some habilities, and all of them give bonuses/level in Health Points (but you can increase HP with points), Turn, and a few other things about supernatural powers.
When you choose a class, you only choose a development pattern. There are no RP obligations as in DD. Someone from the "Paladin" class is only a good warrior who is good in social skills (Command, etc.), there are not Sacred warriors with codes of conducts. Your RP character concept, behaviour, social position, job are only up to you, not decided by your class.
Some class samples : Warrior, Acrobatic warrior, Paladin and Dark Paladin (bad names, just two different versions of the same thing, not "a good" and "a bad" one), Shadow (furtive warrior), Explorer (not sure about the english name), Wizard, Warlock (fighter wizard), Tao (martial arts mainly), Technician (specialist about Ki), Mentalist, Warrior Mentalist, Summoner, Warrior summoner, Wizard mentalist, Rogue, Illusionist (bad name again, just a furtive wizard, not linked to illusions), Novel (no specialisation) etc.
Anima is a very different game than DD, you'll see... Don't have if you had a lot of other experiences in RPG, but you'll need to change a lot of points of view ^^
For example, there are no Priest class, and the game don't need any. If you want to play a priest, you can choose every class depending of your character concept : a little village priest ? Explorer, Novel. A big town bishop ? Novel, Paladin. A pious knight ? Paladin, warrior, Weapon Master. A Saint (someone with supernatural powers recognized by the Church as Divine Gift) ? Wizard, Mentalist, Wizard mentalist, Warlock, etc.