Otomesostoma auditivum is a free-living, hermaphroditic flatworm in the order Proseriata, found in brackish and freshwater environments.

[2] It is a palearctic species living in shallow-water coastal habitats, and occurring in some freshwater lakes far from the sea.

This flatworm was first described in 1874 by the French zoologist Georges Du Plessis who gave it the name Mesostoma auditivum.

It is a holarctic species and has been recorded from the North Atlantic Ocean and the Baltic Sea, including United States, Greenland, Iceland, Finland, Sweden, Germany, Ireland, United Kingdom, Italy, Switzerland, the Ural Mountains and Lake Baikal.

[4] In Lake Baikal, it coexists with endemic related species of flatworm in the shallows, its first record in Asia and a rare example of the Palearctic and Baikalian faunas coming into contact with each other.