In Metroid Prime we had Baby Sheegoths, little monsters known for how disturbingly easy they are to kill, despite their aggressive appearance. In Metroid Prime 2: Echoes,

Geemers, often considered to be the lowest creatures to ever exist. So why was the this sad creature chosen for this issue’s “Monster of the Month” article, instead of the creature that gave the series it’s namesake? Because no other monster in the Metroid series has been as popular with the fans as the Geemer. [...]