Rediscovery of a type specimen of Plehnia arctica (Plehn, 1896) (Polycladida, Plehniidae) described by Marianne Plehn, a pioneering woman in German zoology

The rediscovered type specimen of the polyclad flatworm Plehnia arctica (Plehn, 1896), collected during Kükenthal’s 1889 Spitzbergen expedition and presumed lost for more than a century, was rediscovered in the collection of the Phyletisches Museum Jena (PMJ). The specimen was reexamined and compared with Plehn’s original description. High-resolution images of the type specimen were taken for the first time, and a short historical overview of Marianne Plehn, the first female professor in Bavaria, as well as of the expedition of Kükenthal and Walter to Spitzbergen (Norway), is provided. The whereabouts of the syntypes are clarified, and the specimen is made accessible for further scientific research. More broadly, the study highlights the value of historical collections, even those that are unprocessed or insufficiently curated.