The Alpha Metroid is the third stage (fourth if counting the egg) of a typical Metroid's life cycle, appearing in two games, Metroid II: Return of Samus and Metroid Fusion. When a Larval Metroid reaches the Alpha stage, the transparent upper membrane becomes the underbelly (where it remains for the rest of its life cycle), while a plated exoskeleton grows along the dorsal region. This exoskeleton has two compound eyes, a central horn, two small tusks, and four budding limbs where the mandibles once were. Instead of the three nuclei that earlier Metroid stages possess, the Alpha and its following molts up to the Omega Metroid stage bear only a single nucleus; it is unknown what becomes of the other two.