The importance of natural history museums is often underappreciated, but they provide society with a number of services. Among these, they are a fundamental tool for assessing extinction rates and range contractions, or the only way to access species extinct in historical times. In this perspective, we describe here the collection of Unionida of the Museo di Zoologia dell’Università di Bologna, containing one extinct (Epioblasma haysiana) and nine threatened species, plus another 47 species. The collection was built in the mid-19th century and potentially provides baseline information for specialists. In the fragmented natural history museum system of Italy, this might be just the tip of the iceberg of a significant and important amount of material collected in the 19th and early-20th century.