Borg sphere

The Borg sphere was a type of huge sphere-shaped starship used by the Borg. They were part of the fleet of the Borg-Cybermen alliance along with Borg Cubes and Cyber-ships. (IDW: Assimilation²)

Behind the scenes
The Borg sphere is, after the Borg Cube, the most common type of Borg ship to be seen in Star Trek, having appeared in the movie ' and various times in the spin-off series '. In-universe, their appearance in Assimilation² takes place before years before their on-screen appearances.