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The Alpha Metroid is the third stage (fourth if counting the egg) of a typical Metroid's life cycle, appearing in three games, Metroid II: Return of Samus, Metroid Fusion and Metroid: Samus Returns.

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.

Samus Aran encountered fifteen Alpha Metroids during her mission to SR388.


The Alpha Metroid has very basic and straightforward movements, so it doesn't pose any large threat. Five Missiles on the tender underside will take this creature down. Its only means of attack is ramming, as it lacks the jaws of its predecessor, making it one of the weakest stages of a Metroid's natural life cycle.

In Samus Returns, the Alpha Metroid has new attacks. It will attempt to ram Samus, which she can parry with her Melee Counter, and it will drop electrical projectiles, which Samus can destroy for pickups.


"This the [sic] shape of a Metroid after its first molting."


  • Mochtroids, failed artificial replications of Metroids made by Space Pirates, also possess a single nucleus.
  • Metroid: Alpha Type is mentioned in Metroid Prime.
  • The transition from a mature Larval Metroid to an Alpha Metroid causes the disappearance of all but one nucleus in the latter's translucent membrane. Though never explained in the series, it can be assumed that the missing nuclei from the former were re-purposed to create the Alpha Metroid's exoskeleton, eyes, limbs and etc, which will in turn grow to become all the features displayed by the later stages.
    • The membranes of Alpha, Gamma, Zeta and Omega Metroids on SR388 are readily susceptible to concussive weaponry, contrary to the larva's invulnerability unless exposed to cold temperatures. This disparity in defensive strength may be determined by the number of nuclei present in their bodies: the Larval Metroid's membrane is sustained by several nuclei but all later stages in the life cycle carry only one nucleus within.


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