Genital morphology differentiates three subspecies of the terrestrial slug Arion ater (Linnæus, 1758) s. l. and reveals a continuum of intermediates with the invasive A. vulgaris Moquin-Tandon, 1855 Author Reise, Heike Author Schwarzer, Anne-Katrin Author Hutchinson, John M. C. Author Schlitt, Bettina text Folia Malacologica 2020 2020-03-13 28 1 1 34 http://dx.doi.org/10.12657/folmal.028.001 journal article 10.12657/folmal.028.001 545b2a3f-10d0-4c1d-8136-301d98a3d1d2 4615365 LINNAEUS (1758: 652) described both A. ater and A. rufus . If we consider these taxa as conspecific, which name has priority depends on the first reviser. Already MÜLLER (1774: 2) treated ater as having priority, but he did not mention the name rufus (he used the earlier name subrufus for what LINNAEUS (1758) called rufus ), so cannot count as a reviser. At latest, FLEMING (1822: 572) explicitly treated A. rufus as a variety of A. ater , and this is the priority consistently followed by others who consider the taxa conspecific. The nominotypical A. ater ater ( Linnaeus, 1758 ) is our AR morphotype,