When a head of a two-headed ammonite Mutant becomes detached by Kamen Rider Black, it ends up with a young boy and it becomes his new pet.
茂少年がひろった不思議な生物マルモ。それはアンモナイト怪人の体の一部だった。マルモを求め、茂を狙うアンモナイト怪人。
