Type specimens are the permanent reference materials that zoological taxonomy depends upon, serving as the foundation for identifying and classifying species. Their preservation, documentation, and accessibility are essential for maintaining taxonomic stability and enabling future systematic research. Yet museum collections often contain materials that remain overlooked, misplaced, or insufficiently curated for decades, sometimes because of financial limitations but also because of a lack of specialist taxonomic knowledge, an unknown repository, or the absence of type designations. In the nineteenth century, designating types was not even a standard practice, as the first authoritative zoological code was not published until 1905. The rediscovery of such material provides important opportunities to reassess historical descriptions using modern methods and to clarify unresolved taxonomic questions.

The story begins in 1889, when Wilhelm Georg Kükenthal, newly appointed Ritter Professor für Phylogenie at the University of Jena, and Alfred Walter embarked on an Arctic expedition to East Spitzbergen. Financially supported by the Geographical Society in Bremen, the expedition departed from Tromsö on 7 May, guided by the famous walrus hunter and captain Nils Johnsen. The journey suffered an unintended interruption when the ship ran aground and was crushed by pack ice on 11 June near the Kong Ludvigøyane. Fortunately, the small crew was picked up four days later by the Cecilie Malene from Tromsö, whose captain allowed them to continue their expedition under the same conditions as originally agreed.

The specimens brought back to Jena contained a variety of groups, including annelids, birds, mammals, anthozoans, echinoderms, mollusks, nemerteans, poriferans, bryozoans, tunicates, and some flatworms. The material included numerous specimens new to science. The polyclads, free-living marine flatworms, were given to Arnold Lang, a former student of Ernst Haeckel and a specialist on polyclads who had published a systematically significant monograph on the polyclads of the Gulf of Naples in 1884. Lang, in an unusually progressive manner for the period, passed the polyclads to his talented student Marianne Plehn, who published her examinations in her 1896 dissertation, describing several new species. As was commonly practiced in the nineteenth century, the exact details of where the specimens were stored after examination were omitted, and the locations of such type specimens were often lost.

Marianne Plehn was born on 30 October 1863 in Lubochen, then part of West Prussia. At the age of 27, following the death of her parents, she moved to Zurich to study zoology, botany, and geology. With financial support from her uncle, she finished her studies and passed the exam as a special instructor in natural sciences in 1893. From 1894 to 1896, she worked at the Zoological Institute and the Comparative Anatomical Institute of both the University of Zurich and ETH Zurich, which was highly unusual for a woman at this time, and she was the first to achieve this. She received her doctorate in zoology in 1896 after submitting her dissertation Neue Polycladen in 1895, becoming the first woman to be awarded a doctorate by ETH Zurich.

In 1898, Plehn became an assistant at the Bavarian Biological Experimental Station at the School for Veterinary Medicine in Munich. Together with Bruno Hofer, she is considered one of the founders of fish pathology. She dedicated her life to research and left public appearances to her director, even turning down a position in Vienna. As the first woman in Bavaria, she was awarded the title of royal professor by decree of King Ludwig III on 30 December 1913 for her extraordinary contribution to fish pathology. One year before her retirement, she was promoted to chief curator at the Starnberg research station in 1927, and two years later she received an honorary doctorate from Ludwig Maximilian University Munich, becoming the first woman in Germany to receive the Doctor medicinae honoris causa in veterinary medicine. She died on 18 January 1946 in Grafrath, close to Munich, at the age of 82.

The rediscovery itself came about through the systematic overhaul of previously overlooked collection material at the Phyletisches Museum Jena. During the COVID-19 pandemic, when the museum was closed between 2020 and 2021, the reorganization of some collection material led to the rediscovery of specimens that had been forgotten for decades. Among these, a jar was found containing an almost dried polyclad from Kükenthal’s collection that had been examined and described by Plehn. The small ground-stopper jar still had its historical label attached, stating Turbellarien Acelis arctica Plehn nov. gen; nov. spec. nördl. Eismeer. K. u. W., with a blue 1 written and marked by Haeckel on its right corner. Further proof that the specimen is from the type series examined by Plehn is a note by Haeckel in the catalog of the Zoological Institute, where he added an entry to the zoological collection in 1896 and made a remark confirming the specimen came from Kükenthal’s polyclad collection, examined by Marianne Plehn.

The rediscovered specimen was reexamined and compared with Plehn’s original description. High-resolution photographs of the type specimen were taken for the first time, using a Canon EOS 6D mounted on a macro rail with a Canon MP-E 65 mm macro objective, with single focused images stacked using Zerene Stacker. The remaining fluid in the jar was measured with a manual alcohol meter, and the specimen was carefully transferred into a 70 percent ethanol solution to meet best-practice standards for fluid preservation, starting with 90 percent ethanol and decreasing in 5 percent steps. The historical label was carefully detached from the jar using medical-grade cotton wool soaked in warm water, dried between glass plates, and reinforced on Japanese paper. The preserved specimen measures approximately 55 mm in length and reaches a maximum width of 36 mm, with a thickness of approximately 3 mm in the center. The body is elongated, grayish with white patterns, and largely opaque even when strongly illuminated. The mouth opening is situated centrally on the ventral side, the male and female gonopores are separate, and the female gonopore is surrounded by small concentric shallow furrows. No eyes were visible, consistent with Plehn’s original description.

Three specimens were originally available to Plehn, of which only the specimen from the collection of the Phyletisches Museum Jena is known to remain today. Swedish zoologist Karl Alfred Sixten Bock listed seven locations in his 1913 monograph where P. arctica has been found, who collected it, and where the specimens are stored. Only for the specimens collected by Kükenthal and Walter was no location of storage given. To locate possible further syntypes, inquiries were sent to different institutions where Plehn had worked or that were suspected of possibly having stored a specimen through connections to Haeckel or Lang, including institutions in Germany, Sweden, Denmark, Poland, Switzerland, and Norway. Responses confirmed that no additional type specimens could be located, clarifying the whereabouts of the syntypes and establishing the Jena specimen as the only known remaining syntype.

The rediscovery of this original syntype restores important reference material for polyclad taxonomy and once again underscores the scientific importance of preserving and revisiting historical museum collections. Polyclad systematics started with one of the first phylogenetic hypotheses suggested by Lang in 1884, and since then the classification has undergone various changes, but the phylogeny remains unresolved despite recent molecular approaches. None of the recent phylogenetic studies included a specimen of P. arctica, and the now available type material provides the opportunity to further resolve the phylogenetic relationships of polyclads. Beyond its taxonomic value, the specimen also serves as a tribute to the legacy of Marianne Plehn, an extraordinary woman who was a successful pioneer in an academic world dominated by men, where women were largely excluded from scientific careers. Today, a street in Munich bears her name, a PhD support program commemorates her, and four genera and one family in Polycladida, as well as one genus of Diplostomida, celebrate her contributions to science.

Subject of Research: Rediscovery and reexamination of the type specimen of the polyclad flatworm Plehnia arctica described by Marianne Plehn in 1896.

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

Article References: Bock, B. L. (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, Article e200580. https://doi.org/10.3897/nhcm.3.200580

Image Credits: AI Generated

DOI: 10.3897/nhcm.3.200580

Keywords: Plehnia arctica, Marianne Plehn, polyclad flatworms, type specimens, Phyletisches Museum Jena, natural history collections, Spitzbergen expedition, Ernst Haeckel, taxonomy, women in zoology, Rediscovery, type