The first arc has 5 worlds: Wizard City, Krokotopia, Marleybone, Mooshu, and Dragonspyre. The second arc also has 5 worlds: Celestia, Zafaria, Avalon, Azteca, and Khrysalis. The third arc currently only has two worlds: Polaris and Mirage, with Empyrea coming out later this year.
The side world of Grizzleheim also consists of the Wintertusk zones. There's also Wysteria, bringing the total to 14.
Aquila and the 4 Dungeons aren't really worlds, but just separate zones.
