Rinka

Rinka are small red or green rings of energy that thrive in Tourian. They are endlessly regenerated as they try to prevent Samus from reaching Mother Brain, showing them as a security system for the creature. In Metroid: Zero Mission; if the Rinka are destroyed, they will provide Energy Capsules and Missiles. In Super Metroid they do not.

It is possible that the Rinka defense system made an appearance in Metroid Prime 3: Corruption, when Aurora Unit 313 had energy cannons which shot red spheres quite similiar to the Rinka.

Metroid Manual
"These fireball creatures suddenly appear in the last scene. Lots of them appear but they are not very strong."

Cameos

 * In a microgame called Metroid (microgame) found in WarioWare, Inc.: Mega Microgame$! and WarioWare, Inc.: Mega Party Game$!, has a microgame that re-enacts the fight between Samus and Mother Brain from Metroid. Rinkas are found on the second and third levels.