In 1844, the famous German biologist Fritz Müller published his dissertation about the leech fauna of lakes in Berlin. This study not only addressed the occurrence of leeches in the different lakes, but also contains the description of a new species - Glossiphonia verrrucata (Fr. Müller, 1844). Unfortunately, he never mentioned how many specimens he found and where he deposited the material of his dissertation research. Thus, it came as a surprise that the material appeared in the small leech collection of the Zoological Museum of the University of Greifswald. Here, we provide an overview of the material focusing especially on the four syntypes of G. verrucata. Since this is a rarely found species, we further explored historical material from the type locality, Lake Tegel, held in other museums. Our survey revealed that the material collected by Müller is the only one known to date from the species-rich Lake Tegel, which is inhabited by 14 species of freshwater leeches.

Hirudinida , Lake Tegel, freshwater leeches, ZIMG, Glossiphonia verrucata

The collection of leeches (Hirudinea) of the Zoological Institute and Museum of the University of Greifswald (ZIMG) is considerably small (only 66 specimens), but with 31 taxa the most diverse public collection of leeches in the state Mecklenburg-Vorpommern (Jueg 2015). Nearly all specimens were collected in the 19^th century and are in good conditions considering their age. This collection contains the oldest conserved leeches for the state (1834, coll. Creplin), including seven first records and some other non-palearctic species, which are rarely represented in German natural history collections.

As revealed by Jueg (2015), it also contains four specimens of Glossiphonia verrrucata collected in lake Tegel in Berlin. Unfortunately, the specimen label does not have a collecting date, but it is noted that these specimens were collected and determined by Johann Friedrich Theodor Müller (1822–1897) better known as Fritz Müller – the famous German naturalist who emigrated 1852 to Blumenau (Brazil). Müller is a well-known early advocate of Darwinism (e.g. Müller 1864) and extensively corresponded with Charles Darwin and also other influential biologists of the 19^th century (e.g. Ernst Haeckel). He published nearly 250 articles on life history, morphology, systematics and evolution of plants and animals. The Müllerian mimicry was named after him based on his ground-breaking contributions to the theory of insect mimicry. The life and scientific achievements of this remarkable biologist are summarized in Möller (1915–21) and West (2003, 2016).

Fritz Müller studied mathematics and natural sciences in Berlin finishing 1844 with a dissertation thesis on leeches in the area of Berlin including the redescription of Clepsine tessulata (synonym of Theromyzon tessulatum (O.F. Müller, 1774)) and Clepsine marginata (synonym of Hemiclepsis marginata (O.F. Müller, 1774)) as well as the description of the new species Clepsine verrucata (=Glossiphonia verrucata (Fr. Müller, 1844)). According to Jueg (2015), the Museum of Natural History in Berlin (MfN) does not possess any material from Müller´s work on leeches. Furthermore, Müller did not mention where his material was deposited (see Müller 1844) indicating that the material in the collection of the ZIMG could be indeed the type material of Fritz Müller (Jueg 2015). Here, we investigate this collection further by providing an overview of the collection Fr. Müller, revising the type material of Glossiphonia verrucata as well as presenting an overview of other historical records from Lake Tegel, which is the type locality of this rare species.

Figure 1.

A: The naturalist Fritz Müller in his typical appearance. B: Live specimen of Glossiphonia verrucata collected in the Krakower Lake (Germany) in 2017.

Figure 2.

The type specimens of Glossophonia verrucata in dorsal and ventral view.

The specimens are kept in 80% ethanol and were examined using a MBC-10 stereomicroscope. Images were taken with the BK PLUS Lab system (Dun Inc.) using a Canon 65 mm macro lens mounted on a Canon 5D Mark II camera. Image stacks were captured with Adobe Lightroom and processed using Zerene Stacker under PMax value. Obtained extended focus images were edited using Adobe Photoshop CS 6. All measurements are given in millimeters.

The original description of Glossiphonia verrucata can be found in the dissertation thesis „Hirudinibus circa Berolinum hucusque observatis” of Fritz Müller, but without any remark on the number of collected individuals and also on the fate of the material on which the description is based on (Müller 1844). Thus, it was rather surprising to find a considerable amount of his material in the collection of the ZIMG and that no material is present in the collection of the MfN (Hartwich 1986, Jueg 2015). The reason why the material of Müller is deposited in Greifswald is unclear, but he likely deposited all his dissertation material in the museum during his time in Greifswald where he studied medicine from 1845 to 1849. Moreover, Fritz Müller was already in contact with the founder and director of the Zoological Museum Greifswald, Christian Friedrich Hornschuch (1793-1850), during his dissertation work as he explicitly mentioned Hornschuch in the acknowledgements (Müller 1844).

The main distribution of Glossiphonia verrucata is restricted to the northern Palearctic (Jueg 2013). In Central Europe this species is extremely rare with the exception of the population reported from the river Danube where it was found from Bavaria to Hungary (Nesemann 1997, Nesemann and Neubert 1999). Since 1844, Lake Tegel is often cited as locality for this species (e.g. Johansson 1929, Autrum 1936, Herter 1968, Jueg 2013), but it was not found again since Müller´s study, which is also expressed clearly by Autrum (1936). Considering that G. verrucata is only rarely found (e.g. Jueg 2013), we safely assume that the material in the ZIMG is indeed the type material of this species. Thus, it is also negligible that the label of the type material was written later-on (likely with the entry in the catalogue in 1865). Regarding the occurrence of G. verrucata in Lake Tegel it is of interest, that Kalbe found one specimen in August 1961 around 25 km south of Lake Tegel in the “Jungfernsee” near Potsdam (Kalbe 1965). Both lakes are connected by the river Havel and Kalbe extensively worked in this area studying nearly 3.000 freshwater leeches. Thus, it can be concluded that G. verrucata is extremely rare in this area, but likely present in lakes connected by the Havel which should be addressed in future studies.

We are grateful to Henk Menkhorst (Krimpen aan den Ijssel, Rotterdam, Netherlands) for the translation of the dissertation of Fritz Müller. We further thank Birger Neuhaus (Museum für Naturkunde Berlin), Andreas Schmidt-Rhaesa and Helma Roggenbuck (both CeNak Hamburg, Germany) for provided access to the historical material of leeches in their collections. We thank Clemens Grosser and an anonymous reviewer for providing helpful comments on this manuscript.