One of the preferred freshwater crayfish species in astaciculture is the large parastacid Cherax quadricarinatus, a native to Australia. This crayfish yields good production in warm water, and, therefore, it has been translocated from Australia to other countries. One such country is Uruguay, where the initial attempt in astaciculture is being conducted. In a Uruguayan crayfish farm, a large number of Diceratocephala boschmai (Platyhelminthes, Temnocephalida) were found on the body surface and branchial chamber of C. quadricarinatus. This is the first report of an introduced temnocephalidan in the New World, and of D. boschmai in a locality outside Australia/New Guinea. The original description of D. boschmai was based on a few characters that separated this species from the other Temnocephalida; therefore, a detailed description of the Uruguayan population of D. boschmai is also provided. The conditions in which D. boschmai is found in Uruguay are suitable for its development and reproduction. This raises concern about the effect that its release into the environment might have.