Turcinoemacheilus kosswigi (Bănărescu and Nalbant, 1964) was recorded for the first time in Iran from the River Karoun drainage, which belongs to the Euphrates-Tigris drainage. Formerly believed to be an endemic species in the basin of River Tigris, it is now recorded in the upper River Euphrates basin. This extension of its recorded range makes it likely that it has been overlooked in other parts of the Euphrates-Tigris system. The species is distinguished from all other loaches by the pelvic-fin origin in front of the dorsal-fin origin and having the anus closer to the pelvic-fin base than to the anal fin origin.