Matoran spheres were rounded silver containers in which Makuta imprisoned the Matoran of Metru Nui. These spheres caused the Matoran to go into suspended animation.1
Notes
The Matoran within slept an unnatural sleep, eyes dark, heartlight faintly pulsating. He was still alive but trapped in a slumber which may very well have been endless.2
Matoran spheres were made of protodermis, like everything else.3