Elizaveta D. Varakina

Cladocera are an important component of freshwater zooplankton and serve as proxies in paleoecological reconstructions. However, the similarity of environmental signals reflected in the dominant species structure of contemporary (CC) and subfossil (SC) cladoceran communities remains an open question. The objective of this study is to assess how changes in the dominant species structure of SC correlate with those in CC and with corresponding environmental conditions in artificial ponds. The research was conducted in seven artificial urban ponds in Moscow experiencing various degrees of anthropogenic pressure. Samples of both CC and SC were collected simultaneously from the same locations along a depth gradient: from the littoral zone, through intermediate depths, to the deepest part of each pond. During sampling, the following parameters were measured: depth (DEPTH), temperature, dissolved oxygen concentration, pH, conductivity (COND), oxidation‐reduction potential, blue‐green algae phycoerythrin, blue‐green algae phycocyanin, and chlorophyll a. In total, 22 CC and 26 SC samples were collected; 23 species were identified in the CC samples and 38 species were identified in the SC samples. Although the SC samples contained a greater number of species, several significant taxa from the CC samples were either rarely detected or completely absent from the SC samples. Redundancy analysis (RDA) and k‐means clustering revealed five clusters for CC and four for SC, which were distributed along gradients of Depth and COND. Further analysis revealed synchronous changes in species structure in both CC and SC communities along the COND and DEPTH, which aligns with the established ecological preferences of the taxa. That suggest the structure of CC and SC communities in artificial water bodies—even of small size—mirrors specific patterns, resulting the formation of distinct species assemblages. Shifts in dominant species structure within CC and SC may be useful for reconstructing DEPTH, while COND can only be roughly estimated based on the presence of certain subdominant species. The study also discusses the implications of cladoceran species preservation for reconstructing environmental variables.

Water fleas of the family Moinidae Goulden, 1968 (Crustacea: Cladocera) inhabit ephemeral and permanent water bodies. Like other cladocerans, dormant stages of moinids, namely ephippia (modified molt exuvia) containing resting eggs, play a crucial role for their survival and dispersal. However, in contrast to Daphniidae, moinid ephippia are poorly investigated. In this study based on original and previously published data, we summarize information on the ephippia of the genus Moina Baird, 1850 and discuss their value as a source of information for paleoecological reconstructions. In toto, we analyzed more than 140 ephippia and gamogenetic females of recent and fossil populations from different zoogeographical zones and provide descriptions and illustrations for all revealed types of ephippia, as well as brief comments on taxonomy, ecology and distribution of species and species groups to which they were belonged. Our data on the morphological diversity of moinid ephippia cover only a part of the taxa currently described. However, our brief study revealed a remarkably high diversity of ephippial ornamentation patterns relative to other families of Cladocera. Some patterns of ephippial ornamentation are widely distributed and could be found in different zoogeographical zones. Other types seem to have more local distribution. Based on our observations, the structure of ephippia may be valuable for a preliminary brief identification of species groups, especially small-sized micrura-like taxa. Species with peculiar ephippia also were found, but after closer examination, they may represent groups of sibling species. Unexpected records of M. cf. macrocopa made in the Late Pleistocene of North Yakutia demonstrate that this group previously had a broader distribution range in North-Eastern Eurasia, but it subsequently suffered a mass extinction in that area. From the other side, the Old World lineage of M. macrocopa demonstrates expansion of its distribution in the New World. As an important component of freshwater biota of tropical and subtropical regions as well as regions with arid hot climate, moinids may harbor biogeographical vestiges.We hope that our data will serve as a basis for the special search and identification of their remains, as well as for their incorporation into paleoreconstructions for the tracking of different environmental changes.

Representatives of the genus Ceriodaphnia Dana, 1853 (Cladocera: Daphniidae) are widely distributed worldwide, they are very common in the plankton of many freshwater bodies of different types in temperate and tropical latitudes. However, their taxonomy remains intricate, especially as compared to the genus Daphnia O.F. Müller, 1785. The aim of this study is to redescribe the morphology of Eurasian taxa having a specific (high and triangular) postabdomen, namely C. rotunda (Straus, 1820) and C. laticaudata P.E. Müller, 1867 and list the differences between these two taxa. A population from Republic of Sakha (Yakutia, Asian Russia) is identified as C. cf. laticaudata, and its exact taxonomic status could not be resolved to date due to a limited material and absence of gamogenetic specimens in our collection. Also, we analyse the morphological characters used for identification of common Eurasian taxa with special attention to limb II. All Ceriodaphnia species could be subdivided into four groups according to the size of anterior setae on the inner-distal portion of limb II: the pulchella-group with a single rudimentary seta on endite 4 and no seta on endite 3, the quadrangula group with short setae on endites 3 and 4, the dubia-turkestanica-reticulata-nikolaii group with a single very large seta on endite 4 and a shorter seta on endite 3, and the rotunda-laticaudata group with large setae on endites 4 and 3. Four aforementioned groups could be formed according to ecological preferences rather than their phylogenetic position. A further step-by-step revision of Ceriodaphnia is needed based on morphological and full-genome data for adequate understanding of the genus diversity.

Despite the important advances made in the taxonomy of water fleas (Crustacea: Cladocera), many taxa have not yet been revised. The genus Simocephalus Schoedler, 1858 (Anomopoda: Daphniidae) belongs to understudied groups. During the last forty years, several attempts have been made to use genetic approaches to estimate species diversity within Simocephalus. At the same time, investigations on morphology almost stopped after the last revision of Orlova-Bienkowskaja (2001). The lack of morphological data, even on the most widespread taxa, makes it difficult to apply the remains of this group to paleoecological reconstructions, although Simocephalus ephippia are common in subfossil sediments and fossils of different geological ages. We investigated more than 80 ephippia of recent representatives of the genus from Eurasia and North America, and 45 ephippia from Pleistocene sites of different ages on these two continents. For the first time, we have distinguished three main morphotypes based on the sculpture of the ephippia among the recent representatives. Ephippia of the vetulus-type are covered by polygonal hillocks of moderate height and with prominent processes. This morphotype is the most common in Eurasia, but it could be found on other continents, considering the distribution patterns of the S. vetulus species complex. Ephippia of the vetuloides-mixtus-type are covered by hillocks with processes strongly protruding above the ephippium surface. This morphotype is found only in the Asian part of Russia; it has more localized distribution than the vetulus-type. Ephippia of the serrulatus-type are covered by almost flat hillocks, or with hillocks of moderate height. This morphotype is found in both Eurasia and North America, which may confirm previous genetic data on a close relationship between serrulatus populations from the Eastern Palearctic and North America. Ephippia of the vetulus- and serrulatus-types are found in several Pleistocene localities. Due to lack of information about ornamentation patterns of Simocephalus ephippia of pre-Cenozoic age, we could not estimate the precise time of the morphotype separation. However we may conclude that in the Late Pleistocene the vetulus- and serrulatus-types were broadly distributed in Northern Eurasia and North America. Simocephalus ephippia demonstrate a morphological stasis at least since the Late Pleistocene, or even during longer time. In Maly Chukochiy Cape deposits (Republic Yakutia) we found a sole ephippium presumably belonging to an extinct taxon of Simocephalus. Eastern parts of Northern Eurasia had diverse communities of Simocephalus at the Pleistocene-Holocene boundary, and these then changed analogously to the transformation of Daphnia communities. In the course of our work, we obtained a large set of illustrations of Simocephalus ephippium morphology in different populations. We hope that our study will attract more attention to the taxonomy of modern Simocephalus and its Pleistocene-earlier Holocene subfossil ephippia.