Stefan Clessin  Stefan Clessin (13 November 1833, Würzburg – 21 December 1911, Regensburg) was a German malacologist. 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". He conducted research of fossil mollusks as well as living species. Clessin named more than 90 species of non-marine gastropod mollusks, including: