ARKHANGELSK, December 25. /TASS/. Experts of the Laverov Federal Center for Integrated Arctic Research (the Russian Academy of Sciences' Urals Branch) discovered four new species of freshwater mollusks of the Sphaeriidae subfamily in Russia, Kyrgyzstan and Africa, the project's leader, director of the Center's Institute of Biogeography and Genetic Resources, Yulia Bespalaya, told TASS. In long-term studies the scientists systemized those mollusks and clarified their evolution.

"While studying this subfamily, we have described four new species. We have evaluated the morphology, anatomy, and molecular genetic data. We have used collected typical representatives, and for some species that were once described, we have organized expeditions to typical localities: the Indigirka, the Kolyma, the Yenisei (Rivers)," she said. "One species comes from the Kolyma basin, the second species that we've described comes from Morocco, but it also lives in European countries, like in Macedonia or in Turkey. The third species was in Kyrgyzstan, and the fourth - in the Caucasus."

Sphaeriidae mollusks are small bivalve mollusks widespread in freshwater reservoirs. 25 species are known in Russia. This is one of the few groups of mollusks that have mastered reservoirs in the Arctic, and they are the only representatives of the family living in the Novaya Zemlya archipelago. Their populations are viable, even despite the fact that for winter they literally freeze into the ice. Sphaeriidae are active bio filters, and they are a food source for various birds and fish, including those of economic importance. Quite often these mollusks dominate ecosystems. Their presence and conditions are important in assessing the biodiversity of a reservoir, and this assessment requires a proper taxonomy.

Samples from Caucasus, Siberia, Arctic

Until now, the group's taxonomy has been controversial, and different groups of zoologists were distinguishing different numbers of genera, focusing either on morphological data or on molecular ones. In the new study, the scientists used data from genetic banks and collections of research institutions from various countries and conducted a number of expeditions to the Arctic, Siberia, the Far East and the Caucasus.

"In our study, we have collected the biggest number of presently available DNA sequences, more than 1,000," the scientist said. "Of course, our collections prevailed and earlier studies based on a limited number of sequences, the Siberian one fell out completely, there were no Caucasian species, no Arctic whatsoever, and they could not generalize the material or make a correct taxonomy, because they lacked those samples."

The biologists have studied both mitochondrial DNA and nuclear DNA. According to Alexander Kondakov, a leading researcher at the Center's Laboratory of Molecular Ecology and Biogeography, this way the experts could see a more complete genetic picture. Thus, they have identified seven genera of Sphaeriidae mollusks. The Conventus genus, described by Soviet scientists in 1974, has regained its status. The new Hindupisidium genus was extracted and described for the first time.

From elementary to complex in 125 million years

During the study, the scientists made the subfamily's phylogenetic tree, that is they determined the mollusks' evolutionary relationships between different species and genera. They found that Sphaeriidae are a much older group than it was believed earlier. It developed about 125 million years ago in the territory of modern China and then successfully settled on almost all continents. The researchers found that over time, the mollusks' organisms were getting more complicated - prior to this project, experts did not have a consensus on this issue.

The project featured also scientists from the St. Petersburg and the Surgut State Universities, from the Severtsov Institute of Ecology and Evolution, from the Russian Academy of Sciences' Zoological Institute, from the Sidi Mohamed bin Abdellah University and the Mohammed I University (Morocco). The study's results are published in the Zoological Journal of the Linnean Society.

Zoologists point to necessary further studies of this group of mollusks in Africa, South America and Australia, where they have not been studied enough.