Career
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:
Bythiospeum pfeifferi (Clessin, 1890)
Bythiospeum tschapecki (Clessin, 1882).
