The most latent cladoceran in the Holarctic revealed—sinking Unapertura Sarmaja-Korjonen, Hakojärvi & Korhola, 2000 into the genus Rhynchotalona Norman, 1903 (Branchiopoda: Cladocera: Chydoridae)
The morphology of one of the smallest chydorid cladocerans in the world, Unapertura latens Sarmaja-Korjonen, Hakojärvi & Korhola, 2000 (Branchiopoda: Cladocera: Anomopoda) is studied herein. External features and postabdomen of the adult parthenogenetic female are discussed in detail for the first time, based on an intact specimen from northern Finland. Originally described on Quaternary fossil remains, we investigate the validity of the monotypic genus Unapertura and its position within the Aloninae subfamily, in particular in relation to Rhynchotalona Norman, 1903. As a result, we rename the taxon as Rhynchotalona latens comb. nov., based on morphology. The species, a glacial relict, seems one of the rarest cladocerans in contemporary waters in Finland, yet intact specimens are clearly overlooked and recent remains in surface sediments suggest an Arctic-Alpine distribution in oligotrophic habitats in the Holarctic.
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... This was possible because of the preserved remains of the chitinous exoskeleton of Cladocera [3,4]. However, this species has recently attracted particular interest among taxonomists and paleoecologists [1,5,6]. The species was thought to be a glacial relict associated with modern analogues in periglacial aquatic environments. ...
... Previously, chitinous remains of the species were found only in lakes in Finland, and the species was considered absent in modern zooplankton. However, recent studies have shown that the species is not endemic to Finland and is not extinct at all [5,6]. Both chitinized remains in lake surface sediments as well as actual specimens in Finland and Russia have proven that the species is present in modern cladoceran communities [5][6][7]. ...
... However, recent studies have shown that the species is not endemic to Finland and is not extinct at all [5,6]. Both chitinized remains in lake surface sediments as well as actual specimens in Finland and Russia have proven that the species is present in modern cladoceran communities [5][6][7]. This is confirmed by the recording of this species in the surface sediments in the Pechora River delta (N 68 • 21 ′ 454 ′′ E 053 • 24 ′ 759 ′′ ) [8]. ...
Remains of Rhynchotalona latens (Sarmaja-Korjonen, Hakojärvi et Korhola 2000) were found in the bottom sediments of several glaciogenic lakes in northwestern Russia. Subfossil remains of the species were noted both in the bottom sediments of the Late Pleistocene and Mid-Holocene. We discovered a rare species, R. latens, in the bottom sediments of Lake Medvedevskoye (Karelian Isthmus). This species prefers shallow oligo-mesotrophic lakes with organic sediments and has attracted the interest of scientists around the world as it is considered a glacial relict and has recently been found in surface sediments and as a living population in Finland and Russia.
... 47). The morphology of studied parthenogenetic females was similar to the type specimens from Karelia (Sinev and Dadykin 2022;Van Damme and Nevalainen 2019), including a single oval major head pore (Fig. 5c); lateral pores situated far from midline (Fig. 5c); rounded posterior margin of the headshield . 5c); rounded antero-ventral corner of valve (Fig. 5a) (Sinev and Dadykin 2022). ...
... microcephala Sars, 1890 which mostly occurs in the West Palearctic (Garibian et al. 2020;Taylor et al. 2020). The record of Rhynchotalona latens is the most surprising, as living populations of this species were previously found only in Finland and North European Russia (Ibragimova et al. 2024;Sinev and Dadykin 2022;Van Damme and Nevalainen 2019). However, the specific lifestyle of this species associated with Sphagnum, as well as records of its subfossil remains in several regions of Europe, Canadian Alaska and probably in Central China (Ibragimova et al. 2024;Kattel et al. 2015;Sweetman and Sarmaja-Korjonen 2017), confirm that R. latens has a broad circumpolar distribution, as was proposed before (Ibragimova et al. 2024;Nevalainen et al. 2019). ...
Freshwater microcrustaceans in the southern part of the Kamchatka Peninsula are relatively well-known, however, little research has focused on the northern part of the peninsula. Moreover, relatively few data are available on small water bodies, since most of the studies focused on large lakes and estuarine waters. Here, we present the first data on the microcrustaceans of Karaginsky Island (Kamchatka, Russia) and the adjacent mainland. A total of 100 species, including Branchiopoda, Copepoda, Ostracoda and Amphipoda, were observed in the studied area, which significantly expands our knowledge about the local fauna. Thirty-five species were newly recorded for the Kamchatka Peninsula, and three taxa were new for the whole territory of Russia. At least four taxa showed striking deviations from the typical morphology. The general faunistic composition of Karaginsky Island appears to be typical of Northeast Asia, with a prevalence of Palearctic and cosmopolitan taxa and a smaller proportion of East Asian and Beringian endemics. The faunistic diversity of Karaginsky Island is still not completely revealed, and more surveys are needed to have accurate estimations of biodiversity there.
... Another species of the same genus in Scandinavia, Rhynchotalona latens [162], was thought to be extinct. Recent intensive surveys in Finnish lakes made it clear that the extant populations had just been overlooked [163,164]. Similar observations can be made for so-called appearances [84,124] of Phreatalona protzi; this is a genus with a very specific, mainly hyporheic ecology that was only recently revised [165]. A so-called new record of "Alona" rustica (according to [166] this belongs to Flavalona) [90,167] in Italy is also a clear case of improved sampling efforts rather than former absence in Italy, as this is a very specific sphagnophilic species (i.e., found mainly in littoral Sphagnum moss) of dystrophic waters that can be easily missed. ...
Non-indigenous species may pose a threat to native ecosystems worldwide. In aquatic environments, invasives may have a negative impact on human food security and livelihoods. Several water fleas (Crustacea: Branchiopoda: Cladocera) are notorious invasive alien species influencing large freshwater lake systems and even inland seas. In the current review, we discuss the state of knowledge regarding non-indigenous species in the Cladocera and their invasiveness potential in different continents. We argue that the potential impacts and occurrence of cladoceran exotics may be higher than generally assumed. We critically review 79 cases from literature sources, involving 61 cladoceran taxa where records outside of their natural distribution ranges were previously interpreted as invasions. We assessed the probability of natural range expansions versus human-mediated introductions and we discuss several major corridors of invasion. We estimate human-mediated transportations for at least 43 taxa (out of 61; ca 70%), while other cases can be seen as natural expansions of their distribution ranges (not necessarily/not likely human-mediated) and/or taxonomical confusion. We confirm non-indigenous presence in recipient regions for at least 41 cladoceran taxa, of which several are true invasives (i.e., with negative impacts on native ecosystems). The majority are zooplankters with effects on pelagic freshwater ecosystems, yet we also report on introductions by littoral taxa. We argue that cryptic introductions of cladocerans are taking place on a global scale, yet they remain under the radar. We highlight several striking case studies, such as the Ponto–Caspian onychopods that have invaded the Baltic Sea and the Laurentian Great Lakes, and several clones of the anomopod genera Daphnia and Bosmina that have successfully colonised new environments, causing equilibria shifts in native aquatic worlds. At the same time, we dispel some myths about taxa that were misconstrued as invasive in certain localities. Based on our review, the first of its kind for freshwater zooplankton, future environmental monitoring tools including molecular techniques and detailed surveys with rigorous and critical taxonomical assessments may help to provide a clearer picture on the extent of invasiveness of cladocerans.
Very rare North European water flea Rhynchotalona latens (Sarmaja-Korjonen, Hakojärvi & Korhola, 2000) (Crustacea: Cladocera), found mostly as remains during subfossil studies, was found in North Karelia, Russia. The species inhabits waterlogged Sphagnum mosses at lake margins, but is not present in littoral zones of the lakes. Morphology of thoracic limbs of R. latens was studied for the first time; SEM studies of the species were conducted for the first time. Our data suggests that R. latens is a specialized interstitial moss-dwelling species, only accidentally found in open water, which explains its rarity in samples taken by standard sampling methods. Presence of R. latens subfossil remains in sediments specifically indicate presence of Sphagnum at the lake coast, typical for acid oligotrophic or dystrophiс lakes.
Independent Arctic records of temperature and precipitation from the same proxy archives are rare. Nevertheless, they are important for providing detailed information on long-term climate changes and temperature-precipitation relationships in the context of large-scale atmospheric dynamics. Here, we used chironomid and cladoceran fossil assemblages to reconstruct summer air-temperature and water-level changes, during the past 400 years, in a small lake located in Finnish Lapland. Temperatures remained persistently cold over the Little Ice Age (LIA), but increased in the 20 th century. After a cooler phase in the 1970s, the climate rapidly warmed to the record-high temperatures of the most recent decades. The lake-level reconstruction suggested persistently wet conditions for the LIA, followed by a dry period between ~1910 and 1970 CE, when the lake apparently became almost dry. Since the 1980s, the lake level has returned to a similar position as during the LIA. The temperature development was consistent with earlier records, but a significant local feature was found in the lake-level reconstruction-the LIA appears to have been continuously wet, without the generally depicted dry phase during the 18 th and 19 th centuries. Therefore, the results suggest local precipitation patterns and enforce the concept of spatially divergent LIA conditions.
A long hidden chydorid (Chydoridae, Cladocera) taxon, first found as fossil specimens and recently redefined as Rhynchotalona latens (Sarmaja-Korjonen et al., Hydrobiologia 436: 165–169, 2000) is investigated for its biogeography and ecology. Late Holocene sediment sequence from Lake Sylvilampi, NE Finnish Lapland, and R. latens spatial distribution in relation to limno-climatic attributes in Finland were examined. Principal component analyses of fossil cladoceran communities showed that R. latens is mostly affiliated with Alonella excisa–Alonopsis elongata–Alonella nana species pool. Generalized linear modeling of R. latens responses to limno-climatic variation indicated that it prefers acidic, mesotrophic, humic and shallow lakes with organic sediments in NE Lapland and has a north boreal-subarctic climatic affiliation. At the northern end of its geographical distribution (NE Lapland), it reproduces with abundant gamogenesis under environmental stress. The specialized taxon is a benthic detritivore and scraper and has a Holarctic northern–alpine distribution. It is a glacial relict associated with modern analogs of periglacial aquatic environments, and it occurs in semi-aquatic wetlands, lush lake littorals and clear and cold waters. Examination of chydorids as bioindicators, especially those with restricted niches, allow us to understand biodiversity responses of lake littorals under changing limno-climatic regimes.
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