Abstract
This paper describes a trematode isolated from the air sacs of a common blackbird (Turdus merula) by the authors in Qaemshahr city, Mazandaran province, north of Iran. The specimens were in the best form to make whole-mounts for species identification. The identified species was Morishitium vagum (Morishita 1924) Witenberg 1928, belonging to the family Cyclocoelidae Stossich 1902, according to morphologic and morphometric characters, as explained in references. This is the first report of a species belonging to the family Cyclocoelidae in Iran, and the first report of this type-species isolated from Turdus merula in the world.