Acanthocyclops sensitivus is a widely distributed European groundwater dwelling cyclopoid. In this study, specimens collected in Austria from the environs of Vienna and the Provinces of Lower Austria and Salzburg are described in detail. A. sensitivus is clearly discernible from other Acanthocyclops species, such as A. venustus, A. gmeineri, A. vernalis and A. robustus, by the morphology of the antennule, ornamentation of the antennal basipodite, the setation of the maxilliped and the seminal receptacle. These differences suggest an only distant relationship between A. sensitivus and the other representatives of this genus (excluding A. parasensitivus).