Stefan Clessin (13 November 1833, in Würzburg – 21 December 1911, in Regensburg) was a German malacologist.
[1] He served as a military officer, and from 1862 worked for the Bavarian railways.
He was an editor of the Malakozoologische Blätter and made major contributions to Martini and Chemitz' Systematisches Conchylien-Cabinet.
[2][3] He conducted research of fossil mollusks as well as living species.
[4] Clessin named more than 90 species of non-marine gastropod mollusks, including:[7]