Octopede

From Wikitroid, the Metroid wiki

Octopedes were small Luminoth-made security drones that patrolled the Sanctuary Fortress. However, they were corrupted by the Ing, causing them to turn against their own creators. Octopedes occupy circular shafts, and lock together to form a chain link. If one is destroyed, the chain would come loose, causing the remaining Octopede to roll around and explode. They resemble small metal balls with a single eye, and besides the small explosions they trigger within themselves, they are quite harmless. They appear only in Metroid Prime 2: Echoes