A revision of Amorphomyces was carried out based on an examination of the author's and type material. Detailed study of the development of the female thallus of Amorphomyces italicus revealed a small, lobate, free, external primary appendage. A free appendage appeared to be lacking in all other known species of the genus. The generic circumscription of Amorphomyces is therefore emended. The new species A. hernandoi, parasitizing the marine aleocharid Diglotta mersa, is described from Portugal. Amorphomyces stipitatus and A. trogophloei are synonymized with A. italicus. With additions and changes, Amorphomyces currently includes ten species. All taxa are illustrated with photographs and line drawings, and a key for their determination is provided.