Cannon

Cannons are small defense mechanisms seen in all appearances of Tourian, in Metroid, Metroid: Zero Mission and Super Metroid. They are seen on the walls and ceilings of Mother Brain's chambers and fire small bullets at Samus. Cannons seem to lack targeting systems, as they swivel and shoot in entirely random directions, regardless of who or what is nearby. However, this particular attack pattern makes them somewhat unpredictable and dangerous, especially when accompanied with the infinitely spawning Rinkas.

Samus can safely stand on top of the Cannons' glowing, circular bases unless they fire a shot directly upwards at her. Their bullets, although not terribly damaging, are a great nuisance, as a direct hit will often knock Samus into the lava below.

These mechanisms can be seen in the blueprints for the future Aurora Unit Complex featured in one of Corruption's preview trailers, and a very similar device known as the Ring Beam Unit is encountered in the Galactic Federation's Bioweapon Research Center in Metroid: Other M.

They are only named in the Metroid (1986 manga).

Trivia

 * In Super Metroid, if the Cannon's fire is shot with a Missile or Super Missile, both shots will extinguish each other.
 * Though never confirmed, it is likely these mechanisms were present within Sector Zero, a replicate of the Tourian base featured in Metroid: Other M.