Scientists at St Petersburg University and the Laverov Centre discover five new species and one genus of leeches in the Arctic

Freshwater leeches, particularly those inhabiting the Arctic waters, are still a little-studied group of animals. In addition, outwardly similar types of leeches often differ greatly in anatomical structure. That makes the process of identifying new species more difficult.

The findings of a joint multi-year study are published in the top-rated Scientific Reports journal.

To study a specimen, biologists place it in absolute alcohol and pour it into a paraffin block. Then, using a specialised device called a microtome, they make very thin longitudinal sections. The number of pieces sometimes exceeds 50 for one specimen. Then, the sections are processed with special dyes making different tissues of the body acquire different colours. That makes the interspecific anatomical differences more obvious.

For molecular genetic analyses confirming interspecific differences, deciphering of the nucleotide sequences of the genes encoding the first subunit of the cytochrome c oxidase (COI) enzyme and the small subunit of ribosomal RNA (18S-rRNA) was used.

The collection of specimens, their processing and analysis of genetic data took about 10 years. The project was supported by the Ministry of Science and Higher Education of the Russian Federation and the Russian Science Foundation.

An analysis of the collected material has shown that the fauna of the Arctic zone of Eurasia includes 14 species of flat leeches (family Glossiphoniidae) belonging to five genera. At the same time, five species and one genus found by the biologists were not previously known to science. In addition, the research team identified the northernmost point of the flat leeches’ range. It is the Taimyr Peninsula.

According to the scientists, the polar hyperboreomyzon (Hyperboreomyzon polaris) is their most interesting discovery. It is a new relict genus and species of leeches, which is endemic to Arctic. It was described as a result of analysing the collections from Kolguev Island and the Putorana Plateau. This is a dark brown pimpled leech, . It is rather large, up to two centimetres in length. Usually, each body segment of flat leeches is divided into three rings. In this species, each of the rings is divided into two more segments.

We could not attribute it to any of the known genera either in terms of morphology or genetics. This is a relic leech, very ancient and rare.

Ivan Bolotov, Director of the Laverov Centre, Corresponding Member of the Russian Academy of Sciences, a co-author of the research

’Surprisingly, this leech has not been discovered by any of the previous scientists. The probable reason is that this species lives only in the most remote and hard-to-reach areas. Yet the hyperboreomyzon is unlikely to be an exclusively Arctic species. We assume that this leech can also be found somewhere in the highlands of Asia, for example, in the Sayan or Altai Mountains,’ said Ivan Bolotov, Director of the Laverov Centre, Corresponding Member of the Russian Academy of Sciences, and a co-author of the research.

According to Ivan Bolotov, this leech is still a mystery. Its lifestyle and nutrition are unknown to scientists. It seems to have lived on the Putorana Plateau for quite a long time. To Kolguev Island, it could come along with migratory birds. Yet these are only preliminary hypotheses that are to be verified.

Scientists at St Petersburg University and the Laverov Centre conducted research in the following areas: Kola Peninsula; Malozemelskaya Tundra; Kanin Peninsula; Kolguev Island; Bolshezemelskaya Tundra; Polar Urals; Yamal Peninsula; Taymyr Peninsula; Putorana Plateau; Kolyma Upland; and Chukotka Peninsula. The work also included information about the fauna of leeches in Arctic Scandinavia, Iceland, and Greenland.

As Professor Maxim Vinarski, Head of the Laboratory of Macro-Ecology and Biogeography of Invertebrates at St Petersburg University, highlights, the discovered leeches are characterised by a significantly darkened colour.

’This is a manifestation of the so-called high-latitude melanism. It is characterised by a darker colour due to the accumulation of pigment, which is typical for Arctic terrestrial organisms. The darker the colour, the more sunlight is absorbed. Arctic waters are shallow, so ultraviolet is able to penetrate to the bottom there. However, it may also be a concealing (cryptic) colouration. The darker you are, the easier for you it is to hide from enemies in dark water or on the dark bottom,’ Maxim Vinarski explained.