Insights into the origin of metazoan multicellularity from predatory unicellular relatives of animals.

BACKGROUND: The origin of animals from their unicellular ancestor was one of the most important events in evolutionary history, but the nature and the order of events leading up to the emergence of multicellular animals are still highly uncertain. The diversity and biology of unicellular relatives of animals have strongly informed our understanding of the transition from single-celled organisms to the multicellular Metazoa. Here, we analyze the cellular structures and complex life cycles of the novel unicellular holozoans Pigoraptor and Syssomonas (Opisthokonta), and their implications for the origin of animals. RESULTS: Syssomonas and Pigoraptor are characterized by complex life cycles with a variety of cell types including flagellates, amoeboflagellates, amoeboid non-flagellar cells, and spherical cysts. The life cycles also include the formation of multicellular aggregations and syncytium-like structures, and an unusual diet for single-celled opisthokonts (partial cell fusion and joint sucking of a large eukaryotic prey), all of which provide new insights into the origin of multicellularity in Metazoa. Several existing models explaining the origin of multicellular animals have been put forward, but these data are interestingly consistent with one, the "synzoospore hypothesis." CONCLUSIONS: The feeding modes of the ancestral metazoan may have been more complex than previously thought, including not only bacterial prey, but also larger eukaryotic cells and organic structures. The ability to feed on large eukaryotic prey could have been a powerful trigger in the formation and development of both aggregative (e.g., joint feeding, which also implies signaling) and clonal (e.g., hypertrophic growth followed by palintomy) multicellular stages that played important roles in the emergence of multicellular animals.

Contrasted Micro-Eukaryotic Diversity Associated with Sphagnum Mosses in Tropical, Subtropical and Temperate Climatic Zones.

Sphagnum-dominated ecosystem plays major roles as carbon sinks at the global level. Associated microbial communities, in particular, eukaryotes, play significant roles in nutrient fixation and turnover. In order to understand better the ecological processes driven by these organisms, the first step is to characterise these associated organisms. We characterised the taxonomic diversity, and from this, inferred the functional diversity of microeukaryotes in Sphagnum mosses in tropical, subtropical and temperate climatic zones through an environmental DNA diversity metabarcoding survey of the V9 region of the gene coding for the RNA of the small subunit of the ribosomes (SSU rRNA). As microbial processes are strongly driven by temperatures, we hypothesised that saprotrophy would be highest in warm regions, whereas mixotrophy, an optimal strategy in oligotrophic environments, would peak under colder climates. Phylotype richness was higher in tropical and subtropical climatic zones than in the temperate region, mostly due to a higher diversity of animal parasites (i.e. Apicomplexa). Decomposers, and especially opportunistic yeasts and moulds, were more abundant under warmer climates, while mixotrophic organisms were more abundant under temperate climates. The dominance of decomposers, suggesting a higher heterotrophic activity under warmer climates, is coherent with the generally observed faster nutrient cycling at lower latitudes; this phenomenon is likely enhanced by higher inputs of nutrients most probably brought in the system by Metazoa, such as arthropods.

Micro-decomposer communities and decomposition processes in tropical lowlands as affected by land use and litter type.

We investigated how the land-use change from rainforest into jungle rubber, intensive rubber and oil palm plantations affects decomposers and litter decomposition in Sumatra, Indonesia. Litterbags containing three litter types were placed into four land-use systems and harvested after 6 and 12 months. Litter mass loss and litter element concentrations were measured, and different microbial groups including bacteria, fungi and testate amoebae were studied. After 12 months 81, 65, 63 and 53% of litter exposed in rainforest, jungle rubber in oil palm and rubber plantations was decomposed. In addition to land use, litter decomposition varied strongly with litter type and short-term effects differed markedly from long-term effects. After 6 months, oil palm and rubber litter decomposed faster than rainforest litter, but after 12 months, decomposition of rainforest litter exceeded that of oil palm and rubber litter, reflecting adaptation of bacteria and fungi to decompose structural compounds in rainforest litter but not (or less) in rubber and oil palm litter. Bacterial and fungal community composition and testate amoeba species number and density varied strongly with litter type, but little with land use. However, community composition of testate amoebae was mainly affected by land use. Generally, changes in bacteria, fungi and testate amoebae were linked to changes in litter element concentrations, suggesting that element ratios of litter material as basal resource for the decomposer food web shape the structure of decomposer communities and decomposition processes via bottom-up forces. Overall, changing rainforest to monoculture plantations shifts the decomposer community structure and negatively affects litter decomposition.

Testing the Effect of Refrigerated Storage on Testate Amoeba Samples.

Samples for analysis of testate amoebae and other protists frequently need to be stored for many months before microscopy. This storage commonly involves refrigeration, but we know that testate amoebae can live and reproduce in these conditions. This raises the question: do communities change during storage and how might this effect the data produced? We analysed Sphagnum samples over a 16-week period to address this question. Our results show no evidence for detectable change. This is a reassuring result supporting much current practice although we suggest that frozen storage or the addition of a fixative may be worthwhile precautions where feasible.

Ecological and evolutionary processes involved in shaping microbial habitat generalists and specialists in urban park ecosystems.

Microbiomes are integral to ecological health and human well-being; however, their ecological and evolutionary drivers have not been systematically investigated, especially in urban park ecosystems. As microbes have different levels of tolerance to environmental changes and habitat preferences, they can be categorized into habitat generalists and specialists. Here, we explored the ecological and evolutionary characteristics of both prokaryotic and microeukaryotic habitat generalists and specialists from six urban parks across five habitat types, including moss, soil, tree hole, water, and sediment. Our results revealed that different ecological and evolutionary processes maintained and regulated microbial diversity in urban park ecosystems. Under ecological perspective, community assembly of microbial communities was mainly driven by stochastic processes; however, deterministic processes were higher for habitat specialists than generalists. Microbial interactions were highly dynamic among habitats, and habitat specialists played key roles as module hubs in intradomain networks. In aquatic interdomain networks, microeukaryotic habitat specialists and prokaryotic habitat specialists played crucial roles as module hubs and connectors, respectively. Furthermore, analyzing evolutionary characteristics, our results revealed that habitat specialists had a much higher diversification potential than generalists, while generalists showed shorter phylogenetic branch lengths as well as larger genomes than specialists. This study broadens our understanding of the ecological and evolutionary features of microbial habitat generalists and specialists in urban park ecosystems across multi-habitat. IMPORTANCE: Urban parks, as an important urban greenspace, play essential roles in ecosystem services and are important hotspots for microbes. Microbial diversity is driven by different ecological and evolutionary processes, while little is currently known about the distinct roles of ecological and evolutionary features in shaping microbial diversity in urban park ecosystems. We explored the ecological and evolutionary characteristics of prokaryotic and microeukaryotic habitat generalists and specialists in urban park ecosystems based on a representative set of different habitats. We found that different ecological and evolutionary drivers jointly maintained and regulated microbial diversity in urban park microbiomes through analyzing the community assembly process, ecological roles in hierarchical interaction, and species diversification potential. These findings significantly advance our understanding regarding the mechanisms governing microbial diversity in urban park ecosystems.

Biodiversity of testate amoebae in Sphagnum bogs: the dataset from forest-steppe ecotone (Middle Volga Territory, Russia).

Background: Testate amoebae are a polyphyletic group of unicellular eukaryotic organisms that are characterised by a rigid shell and inhabit mostly freshwater and terrestrial ecosystems. They are particularly abundant in peatlands, especially in Sphagnum-dominated biotopes. Peatland hydrology is the most important influence on testate amoebae communities. The good preservation of the shells in peat deposits and their response to hydrological regime changes are the principles for palaeohydrological reconstructions. Any changes in the water balance of mires should be expected to have far-reaching effects on biogeochemical cycles, productivity, carbon dioxide and methane exchange. New information: This paper presents a dataset (Darwin Core Archive - DwC-A) on the distribution of Sphagnum-dwelling testate amoebae in nine mires located in the forest-steppe subzone of the East European Plane. The dataset includes information about 86 taxa belonging to 29 genera and contains 3,123 occurrences of 49,874 individuals. The following environmental variables are provided: microtopography, oxidising and reducing potential, total mineralisation, substrate temperature, acidity, substrate wetness and water table depth. These data might be used for biogeographical and palaeoecological studies, including quantitative reconstructions.

Evolution of seed characters and of dispersal modes in Aizoaceae.

The family Aizoaceae includes ~1880 species and is one of the more diverse groups within Caryophyllales, particularly in arid areas in the western part of southern Africa. Most species are dwarf succulent-leaf shrubs. In response to the harsh climatic conditions prevalent where they occur, many representatives have evolved special reproductive adaptations. These include hygrochastic capsules (mostly found in Mesembryanthemoideae and Ruschioideae), burr-like indehiscent and one-seeded, winged diaspores, and fast germination of seeds after rain. We focused on anatomical features, evolutionary trends, and the ecological significance of various morpho-anatomical structures found in the seeds. The seeds of 132 species from 61 genera were studied, and 18 diagnostic characters were discovered. All studied characters were compared with those of other families from core Caryophyllales. The seed notch and embryo shape were added to the list of characteristics distinguishing major clades within the family. In addition, the presence of longitudinal ridges and a keel on the seed are additional characters of Aizooideae and combined Ruschioideae-Apatesieae, respectively. Puzzle-like borders of testa cells are a common trait in Ruschioideae and Mesembryanthemoideae. Most taxa in Aizoaceae have a thin seed coat, which is the ancestral state within the family. This may facilitate fast germination. We observed several shifts to a medium-thick or thick seed coat in members of Ruschioideae and Acrosanthoideae. These inhabit fire-prone environments (in vegetation types known as fynbos and renosterveld), where the thickened seed coat may protect against damage by fire. Multi-seeded fruits are the ancestral state within Aizoaceae, with several shifts to one-(two-)seeded xerochastic fruits. The latter are dispersed via autochory, zoochory, or anemochory. This trait has evolved mainly in less succulent subfamilies Acrosanthoideae, Aizooideae, and Sesuvioideae. In highly succulent subfamilies Ruschioideae and Mesembryanthemoideae, fruits are almost exclusively multi-seeded and hygrochastic with ombrohydrochoric dispersal. A reduction in the number of seeds within a dispersal unit is rare. Within Apatesieae and Ruschieae, there are also a few unusual genera whose fruits fall apart into one- to two-seeded mericarps (that are mainly dispersed by wind).

Community assembly and co-occurrence network complexity of interstitial microbial communities in the Arctic (investigation of ciliates in the White Sea intertidal zone).

Arctic coastal ecosystems play a major role in global environmental system and have been altered significantly by climate changes. To better understanding the response of marine coastal ecosystems towards rapid Arctic climate changes, we examined the variation in diversity and community structure and provided insights into the co-occurrence network and community assembly of interstitial ciliates in the Kandalaksha Gulf of the White Sea from 2009 to 2019. Co-occurrence networks analysis indicated considerably high ration of positive correlations within a community that indicated low competition between interstitial ciliate species. Furthermore, we found that contribution of stochastic processes to the ciliate community assembly was insignificant. Compare with earlier data from the same ecosystem obtained in 1980s-1990s, the role of competitive factors is decreasing, and communities are becoming more spatially and temporally homogeneous. This community simplification is likely due to the response of the entire intertidal ecosystem to global climate change in Arctic.

Linking biodiversity and ecological function through extensive microeukaryotic movement across different habitats in six urban parks.

Highly diverse but divergent microeukaryotes dwell in all types of habitats in urban park ecosystems. Extensive microbial migration occurs between both terrestrial and aquatic habitats. Microbial movement is beneficial to the maintenance of biodiversity and the exchange of functional guilds.

Distribution of soil testate amoeba assemblages along an elevation gradient on Mount Fuji (Japan).

Elevation gradients have been useful to study distributional patterns of soil organisms since the time of Humboldt but only recently these patterns have been studied for soil microorganisms. Here we report the results on species diversity and composition of soil- and moss-dwelling testate amoeba assemblages along a 1400 m elevation gradient (904-2377 m a.s.l.) on Mount Fuji (Japan) from temperate forest to alpine vegetation. In total, 95 testate amoeba taxa belonging to 29 genera were identified. The core of testate amoeba assemblages was formed by ubiquitous species such as Trinema lineare, Euglypha laevis, Cryptodifflugia oviformis, and Trinema complanatum. However, several taxa with limited geographic distribution were also observed (e.g., Centropyxis latideflandriana, C. stenodeflandriana, Plagiopyxis cf. barrosi, Heleopera rectangularis, and Distomatopyxis couillardi). Species diversity indices (species richness and Shannon's index) were characterised by bell-shaped patterns peaking at âˆ¼ 1700 m in the subalpine mixed conifer-deciduous forest. The species composition of testate amoeba assemblages was best explained by the vegetation types which accounted for 12.3% of the total variation. Overall, these findings indicate that elevation effects on species composition of testate amoeba assemblages are strongly mediated by vegetation.

Recent climate change has driven divergent hydrological shifts in high-latitude peatlands.

High-latitude peatlands are changing rapidly in response to climate change, including permafrost thaw. Here, we reconstruct hydrological conditions since the seventeenth century using testate amoeba data from 103 high-latitude peat archives. We show that 54% of the peatlands have been drying and 32% have been wetting over this period, illustrating the complex ecohydrological dynamics of high latitude peatlands and their highly uncertain responses to a warming climate.

Meisterfeldia bitsevi-new testate amoeba of the family Cryptodifflugiidae Jung, 1942 (Amoebozoa: Arcellinida) from the tree hollow in the urban park (Moscow, Russia) with a key to species of the genus Meisterfeldia.

The new testate amoeba species Meisterfeldia bitsevi is described from the linden-tree trunk hollow in the urban park in Moscow (Russia). New species is characterized by elongated ovoid bilaterally symmetrical shell, which is laterally not compressed. The shell is composed of proteinaceous material without mineral particles. Almost circular subterminal aperture is placed on ventral side. The key to the species of the genus Meisterfeldia is developed.

Temporal variability of Pu signatures in a 210Pb-dated Sphagnum peat profile from the Northern Ural, Russian Federation.

The peat archives are one of the stratigraphic records revealing clearly physical, chemical and biological signals of human influence on the Earth System since the 1950s, at least. The presented study was aimed mainly to identify the level and origin of anthropogenic radionuclides such as 238, 239, 240Pu in a 210Pb-dated peat profile derived from the Northern Ural, Russian Federation. As stated, the vertical variability of 240Pu/239Pu isotopic compositions reflects the nuclear weapons testing history with the maximum in the 1960s and small regional impact most likely of high-yielded tests in the 1950s as well as Chinese detonations in the 1970s. Peat accumulations rates were similar to those obtained in adjacent areas, whereas 210Pb flux slightly exceeded the reference level established for adequate latitude belt.

Decade-scale change in testate amoebae community primarily driven by anthropogenic disturbance than natural change in a large subtropical reservoir.

Understanding the extent of human activities leading to an influx of chemical pollutants that cause substantial environmental transformations is the focus of much ongoing research. In this study, we present a multi-proxy record based on a sediment core from a large subtropical reservoir (Xinfengjiang Reservoir) in south China with an emphasis on the changes in testate amoebae community, in combination with sedimentological (radioactivity, physicochemistry, nutrient and organochlorine pesticides) and climatological (air temperature and precipitation) data over the last three decades. Twenty-seven testate amoebae species belonging to seven genera (Arcella, Centropyxis, Cyclopyxis, Difflugia, Netzelia, Euglypha and Pseudodifflugia) were observed. Species richness, abundance and biomass of testate amoebae were in ranges of 18-26 species, 616-825 ind. ml-1 and 9.0-19.4 µg C ml-1, respectively. Two development stages of the reservoir, dated to 1978-1993 (stage 1) and 1993-2006 (stage 2), were distinguished based on testate amoebae communities. Stage 1 was characterized by elevated dry bulk density, carbon-to­nitrogen ratio and p,p'-DDE in the sediment core and an impact of nitrogen and sulfur deficiency on testate amoebae. Stage 2 was marked by a decrease of dry bulk density, elevated concentrations of aluminum, iron and carbon, low carbon-to­nitrogen ratio and organochlorine pesticides, fluctuations in rainfall on shorter and yearly timescales, and a stronger influence of the organochlorine pesticides on testate amoebae. Testate amoebae community change and the identified two-stage development were consistent with atmospheric deposition of organochlorine pesticides from anthropogenic sources inside and outside the reservoir watershed, nutrient influx and sediment physicochemistry. The testate amoebae community dynamics and a strong community-environment relationship in stage 2 were linked with non-random patterns in the biotic neighborhoods of species (deterministic processes). The results suggest a stronger impact of anthropogenic disturbance than natural environmental change on testate amoebae community variation of Xinfengjiang Reservoir over time.

Key periods of peatland development and environmental changes in the middle taiga zone of Western Siberia during the Holocene.

The response of peatlands to climate change can be highly variable. Through understanding past changes we can better predict the response of peatlands to future climate change. We use a multi-proxy approach to reconstruct the surface wetness and carbon accumulation of the Mukhrino mire (Western Siberia), describing the development of the mire since peat formation in the early Holocene, around 9360 cal. year BP. The mire started as a rich fen which initiated after paludification of a spruce forest (probably in response to a wetter climate), while the Mukhrino mire progressed to ombrotrophic bog conditions (8760 cal. year BP). This transition coincided with the intensive development of mires in Western Siberia and was associated with active carbon accumulation (31 g m-2 year-1). The ecosystem underwent a change to a tree-covered state around 5860 cal. year BP, likely in response to warming and possible droughts and this accompanied low carbon accumulation (12 g m2 year-1). If the future climate will be warmer and wetter, then regional mires are likely to remain a carbon sink, alternatively, a reversion to the wooded state with reduced carbon sink strength is possible.

Evolutionary relationships, biogeography and morphological characters of Glinus (Molluginaceae), with special emphasis on the genus composition in Sub-Saharan Africa.

Glinus is a small genus of Molluginaceae with 8-10 species mostly distributed in the tropics of the World. Its composition and evolutionary relationships were poorly studied. A new molecular phylogeny constructed here using nuclear (ITS) and chloroplast (rbcL, trnK-matK) markers confirmed the monophyly of the genus. Based on ITS analysis, the following well-supported lineages are present within Glinus: the G. bainesii lineage is recovered as sister to the remainder of the genus followed by G. oppositifolius. Three other clades are: G. hirtus with G. orygioides; G. radiatus and G. lotoides; the latter is represented by a sample from North America, and G. zambesiacus as sister to G. setiflorus + G. lotoides + G. dictamnoides. On the plastid gene tree, G. bainesii + G. oppositifolius form a sister clade to all other Glinus species. The next clade is formed by G. hirtus and G. orygioides followed by G. radiatus plus an American sample of G. lotoides. The next branch comprises G. setiflorus as sister to G. zambesiacus + G. lotoides + G. dictamnoides. Glinus seems to have originated from Africa around the Late Eocene or Early Miocene, with further radiations to Australia and the Americas during the Late Miocene or Late Pliocene. Compared with the previous limited character set used for the diagnostics, we have found ten new morphological and carpological traits distinguishing Glinus members. In both trees based on nuclear and plastid datasets, the major phylogenetic clades cannot be characterized by the peculiar morphological characters. Many shared character states leading to their contrasting pattern in the multivariate analysis model are interpreted as a high homoplasy in the phylogenetically distant species. We paid special attention to the composition of the genus in Sub-Saharan Africa, a region with the greatest species diversity. Our results provide new insight into the taxonomy of Glinus in this region. Glinus lotoides var. virens accepted in many previous works is a synonym of G. dictamnoides that is closely related to G. lotoides based on molecular analysis and morphological characters. The status of the American populations of G. lotoides needs further investigation due to different characters of the specimens from the Old and the New World. Many specimens previously identified as G. lotoides var. virens and as the intermediates G. lotoides × G. oppositifolius belong to G. zambesiacus sp. nov. and G. hirtus comb. nov. (≡ Mollugo hirta); the latter species is resurrected from synonymy after 200 years of unacceptance. In some African treatments, G. hirtus was known under the invalidly published name G. dahomensis. Glinus zambesiacus is distributed in the southern and eastern parts of tropical Africa, and G. hirtus previously assumed to be endemic to West Africa is indeed a species with a wide distribution across the tropical part of the continent. Glinus microphyllus previously accepted as endemic to West Tropical Africa together with other new synonyms (G. oppositifolius var. lanatus, G. herniarioides, Wycliffea rotundifolia) is considered here as G. oppositifolius var. keenaniicomb. nov. (≡ Mollugo hirta var. keenanii), a variety found across the entire distribution of G. oppositifolius (Australia, Asia, and Africa). The presence of the American G. radiatus in Africa is not confirmed, and all records of this species belong to G. hirtus. The lectotypes of some names (G. dictamnoides, G. herniarioides, Mollugo hirta, M. setiflora, Pharnaceum pentagynum, Wycliffea) as well as a neotype of G. trianthemoides are designated. A new key to the identification of all Glinus species in Sub-Saharan Africa is provided. A checklist is given of all accepted species in this region (G. bainesii, G. hirtus, G. lotoides, G. oppositifolius s.l., G. setiflorus, and G. zambesiacus) with their nomenclature, morphological description and geographical distribution.

Size compartmentalization of energy channeling in terrestrial belowground food webs.

Size-structured food webs form integrated trophic systems where energy is channeled from small to large consumers. Empirical evidence suggests that size structure prevails in aquatic ecosystems, whereas in terrestrial food webs trophic position is largely independent of body size. Compartmentalization of energy channeling according to size classes of consumers was suggested as a mechanism that underpins functioning and stability of terrestrial food webs including those belowground, but their structure has not been empirically assessed across the whole size spectrum. Here we used stable isotope analysis and metabolic regressions to describe size structure and energy use in eight belowground communities with consumers spanning 12 orders of magnitude in living body mass, from protists to earthworms. We showed a negative correlation between trophic position and body mass in invertebrate communities and a remarkable nonlinearity in community metabolism and trophic positions across all size classes. Specifically, we found that the correlation between body mass and trophic level is positive in the small-sized (protists, nematodes, arthropods below 1 µg in body mass), neutral in the medium-sized (arthropods of 1 µg to 1 mg), and negative in the large-sized consumers (large arthropods, earthworms), suggesting that these groups form compartments with different trophic organization. Based on this pattern, we propose a concept of belowground food webs being composed of (1) size-structured micro-food web driving fast energy channeling and nutrient release, for example in microbial loop; (2) arthropod macro-food web with no clear correlation between body size and trophic level, hosting soil arthropod diversity and subsidizing aboveground predators; and (3) "trophic whales," sequestering energy in their large bodies and restricting its propagation to higher trophic levels in belowground food webs. The three size compartments are based on a similar set of basal resources, but contribute to different ecosystem-level functions and respond differently to variations in climate, soil characteristics and land use. We suggest that the widely used vision of resource-based energy channeling in belowground food webs can be complemented with size-based energy channeling, where ecosystem multifunctionality, biodiversity, and stability are supported by a balance across individual size compartments.

Frenopyxis stierlitzi gen. nov., sp. nov.-new testate amoeba (Amoebozoa: Arcellinida) from the urban parks with notes on the systematics of the family Centropyxidae Jung, 1942.

New species, Frenopyxis stierlitzi, is described from tree hollows in the urban parks in Moscow (Russia) and Potsdam (Germany). The species belongs to the new genus of the family Centropyxidae and characterized by unique character, i.e. an internal thick organic lip surrounding an aperture and continuing in a bridle, which connects an aperture with the internal side of a shell wall and broaden in the place of connection of a bridle and a shell wall. The systematics of the family Centropyxidae is discussed and the importance of the structures, which divide inner shell volume into compartments, is underlined.

Erratum: Future Temperature Extremes Will Be More Harmful: A New Critical Factor for Improved Forecasts.

The authors would like to correct the names and surnames of both authors of their previous paper [1] as follows [...].

Morphology of testate amoeba Difflugia australis (Playfair, 1918) Gautier-Lièvre et Thomas, 1958 from a subtropical reservoir (southeast China).

Difflugia australis, first described by Playfair (1918), has a unique morphotype. However, in the absence of morphometric data, it has not yet been reliably classified within the largest testate amoeba genus Difflugia. In this study D. australis collected from a subtropical reservoir in southeast China was investigated by means of light and scanning electron microscopy. Basing on biometrical data, we provide an improved diagnosis of this little known species. Difflugia australis is different from other similar congeners (i.e., D. bacillariarum Perty, 1849 and D. elegans Penard, 1890) mainly by the combination of the following features: the shell is broadly ovate, with rounded dome and convex sides converging down to a very short distance from the aperture and diverging suddenly into a short rim (collar). It is usually more or less asymmetrical, with one side being more dilated than the other. The shell surface is slightly smooth, composed of flat siliceous plates of irregular shape and size, mixed with fine grains; microbial spores of comparable forms are spread on the shell surface; particles are often interspersed with a network of organic cement with unique mesh pattern; one (sometimes two) slanting spine-like posterior end of the shell is variable in form; collar is mainly formed by small plates of equal size. The dimensions of the shell are: total shell length 88-106 µm; shell width 53-88 µm; aperture diameter 19-28 µm; collar height 3-6 µm; spine length 3‒23 µm. The size frequency distributions of both total shell length and shell width indicate that it is a size-monomorphic species with low variability.