Some of the best scientific discoveries are not made in the field or the lab, but in the dusty corners of a museum. Bernhard L. Bock, a curator at the Institute for Zoology and Evolutionary Research & Phyletisches Museum at Friedrich Schiller University Jena, has done just that. His study, published open access in Natural History Collections and Museomics (NHCM), describes the rediscovery of a type specimen of the polyclad flatworm Plehnia arctica, presumed lost for more than a century.
A jar nobody was looking for
The specimen was collected in July 1889 during Wilhelm Kükenthal and Alfred Walter’s Arctic expedition to Spitsbergen. The trip nearly ended in disaster when their ship was crushed by pack ice in June, but the crew was rescued four days later and carried on. The flatworms were handed to the zoologist Arnold Lang, who passed them to his talented student, Marianne Plehn. She described the species in 1896 as Acelis arctica, and the genus was later renamed Plehnia in her honour.
As was common in the nineteenth century, no one recorded where the type specimens were kept afterwards, and they simply vanished from the record. The Jena specimen resurfaced when previously forgotten collection material was reorganised, and Bock found a small ground-stopper jar holding an almost dried-out polyclad, with just a little liquid keeping it from drying out completely. Its original label, handwritten by Ernst Haeckel, was still attached. An entry in Haeckel’s own ledger from 1896 confirmed the link to Plehn’s work.
Detective work
Of the three specimens Plehn originally examined, only this one is known to survive. Bock wrote to institutions across Germany, Sweden, Denmark, Poland, Switzerland and Norway in search of the others, without luck. He then carefully rehoused the specimen in 70% ethanol, conserved its fragile label and photographed it in high resolution for the first time. The worm is around 55 mm long and 36 mm wide, and, just as Plehn reported, it has no eyes.
Who was Marianne Plehn?
Bock is keen that the story does not stop at the specimen. Plehn, he explains, is best known for co-founding fish pathology alongside Bruno Hofer:
“She helped lay the foundational framework for fish pathology and treatment. She described and classified various freshwater fish diseases.”
Her research covered parasitic and environmental diseases, including liver and metabolic disorders in salmonids and bacterial infections in commercial fisheries. In 1924 she published the Praktikum der Fischkrankheiten, which “became a standard diagnostic and teaching handbook for zoologists, veterinarians or fisheries managers across Europe for a long time”.
Her path was far from easy. Women in Germany were excluded from higher education until the early 1900s, and were permitted only as “guest listeners” who could not earn degrees. Plehn had to leave the country to study in Zurich, where she became the first woman to receive a doctorate from ETH Zurich. In 1913 she was named Königlicher Professor, the first woman in Bavaria to receive the title.
As Bock notes:
“This represents a historic milestone for women in higher education and natural sciences in Germany – despite no linked teaching certificate to the appointment. Her extensive field research and diagnostic expertise earned her widespread recognition as one of Europe’s top authorities in aquatic biology.”
Why it matters for future research
For Bock, the find carries several hopes. The first is a change in attitude towards neglected collections:
“I made the experience first-hand that the decision of getting rid of something is made quite fast, without having a closer look or starting to sleuth the provenance of certain objects, as this is a very time-consuming and often dead-end job, but sometimes there are astonishing reveals!”
The second is about storytelling. “I want to tell stories, to scholars, students and visitors,” he says. Knowing who collected a specimen, and how, makes an object attractive in a way that a label never could, because “there is more to tell than just a greyish marine flatworm”.
The third is scientific. The relationships of the family Plehniidae within the polyclads remain unclear, and no earlier phylogenetic study has included P. arctica. Bock hopes the specimen might one day yield DNA sequences, making it useful for phylogenetic and systematic research.
A call for more curators
Finally, Bock sees his article as a plea for investment in people as well as in specimens: small museums, he argues, need more curator positions, not only for vertebrates but for other groups too.
“There is so much to discover that is already there, but we lack manpower.”
Asked what he finds most interesting about the work, Bock says it is the discovery itself and its provenance, “as this enriches our collection”. Others, he suggests, may be drawn to the news that a type specimen is available again, or to Plehn’s career path. Whichever it is, a grey flatworm in a small jar has proved to be a window onto a pioneering scientist and a reminder of how much may still be waiting on the shelves.
Original source:
Bock BL (2026) Rediscovery of a type specimen of Plehnia arctica (Plehn, 1896) (Polycladida, Plehniidae) described by Marianne Plehn, a pioneering woman in German zoology. Natural History Collections and Museomics 3: e200580. https://doi.org/10.3897/nhcm.3.200580
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