Macrostomum longituba (Platyhelminthes, Rhabditophora, Macrostomorpha), formerly known as a representative of the Mediterranean brackish-water complex, is recorded for the first time in the Russian freshwater fauna. A single specimen of this species was discovered in 2016 in the Kama widening of the Kuibyshev Reservoir (Kama River) in the epibioses of a sunken boat. The report contains information on the morphology and habitat conditions of this species.