Researchers from the A.N. Severtsov Institute of Ecology and Evolution of the Russian Academy of Sciences (IEE RAS), together with colleagues from Kazan Federal University, the Ust-Lensky Nature Reserve, and the Limnological Institute of the Siberian Branch of the Russian Academy of Sciences, have described a new species of copepod crustaceans from the order Cyclopoida (Copepoda) – Eucyclops sibiricus Novikov, Sharafutdinova, Abramova, Mayor & Chertoprud, 2025. The species has a wide range in Central Siberia, including the Lena River Delta, the Putorana Plateau, the Anabar Plateau, and the Irkutsk Region. This is another find of a new species of freshwater Copepoda in the Arctic.
The genus Eucyclops is one of the most diverse in the order Cyclopoida and has more than 100 species. Morphologically, the species of the genus are often very similar to each other. In this regard, when describing Eucyclops species, an integrative approach is relevant, combining the analysis of morphological aspects, the structure of DNA sequences and ecological features.
The new species E. sibiricus is very similar in body and limb structure to its relative E. speratus (Lilljeborg, 1901). Initially, all finds of this species from Siberia were identified as E. speratus. However, a detailed analysis of mitochondrial and nuclear gene sequences was subsequently performed for E. sibiricus, which clearly confirmed its uniqueness as a new species. Attempts were then made to find differences between the two species. A wide range of methods was used to search for morphological differences. However, qualitative and quantitative macrocharacteristics, morphometry, and the pattern of pores on body segments did not make it possible to distinguish between the species. It turned out that accurate identification can only be made using microcharacteristics that had not previously been used to separate Cyclopoida species. Thus, differences were observed in the arrangement and number of hairs and spines on the limbs and caudal branches. These features are so subtle that without performing a molecular genetic analysis it was not obvious what the researchers were looking at: a new taxon for science or a form of a previously described species?
The use of a variety of approaches to studying morphology did not provide any universal solution for dividing the Eucyclops species complexes. In this case, while the widely used methods were unsuccessful, a long search and counting of small elements made it possible to find differences between the species.
Thus, E. sibiricus and E. speratus should be considered pseudocryptic - having only slight differences in visual characteristics, but clearly distinguishable in their DNA sequences. According to previously published drawings of crustaceans, it is E. sibiricus that is found in Japan and Korea. Probably, the distribution of E. speratus covers the European part, and E. sibiricus - the Asian part of the Palearctic, while in the territory of the East European Plain the ranges of the species overlap.
The research was supported by the grant of the Russian Science Foundation No. 23-24-00054.
The work was published in the journal: Novikov A., Sharafutdinova D., Abramova E., Mayor T., Chertoprud E. 2025. An integrative approach to the delimitation of pseudocryptic species in the Eucyclops speratus complex (Copepoda, Cyclopoida) with a description of a new species expand // ZooKeys. V. 1226. P. 217-260.