Acanthotrema armata n. sp. (Trematoda: Heterophyidae) is described from the gut of Larus audouinii Payraudeau (Aves: Laridae) caught on the Chafarinas Islands in the southwestern Mediterranean (Spain). This trematode differs from other species of Acanthotrema Travassos, 1928 in having two spined, sclerotised pieces in the ventrogenital sac and in the position of the genital pore. Parastictodora Martin, 1950 is considered a synonym of Acanthotrema. As the diagnosis of the genus Acanthotrema was based only on its type-species, it is amended to include the characteristics of the new species and those attributed to Parastictodora.