Unchained Summoner Class Feature.
Created Eidolon, used Extra Evolution feat from Summoner at 1st level.
Created Eidolon, selecting Agathion, then Quadraped. Then attempted to select Claws (Legs) evolution, no luck. Told me it I was not qualified.
Claws are a 1-point evolution that can be placed on any set of limbs, either legs or arms. Agathion can be chosen as a quadraped, which gives the Eidolon two sets of limbs, arms and legs. Not sure why I cannot then place claws on already existing limbs, as intended by the rules.