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Diatoms function as major primary producers, accumulating large amounts of biomass in most aquatic environments. Given their rapid responses to changes in environmental conditions, diatoms are used for the biological monitoring of water quality and for performing ecotoxicological tests in aquatic ecosystems. However, the molecular basis for their toxicity to chemical compounds remains largely unknown. Here, we sequenced the genome of a freshwater diatom, Mayamaea pseudoterrestris NIES-4280, which has been proposed as an alternative strain of Navicula pelliculosa UTEX 664 for performing the Organisation for Economic Co-operation and Development ecotoxicological test. This study shows that M. pseudoterrestris has a small genome and carries the lowest number of genes among freshwater diatoms. The gene content of M. pseudoterrestris is similar to that of the model marine diatom, Phaeodactylum tricornutum. Genes related to cell motility, polysaccharide metabolism, oxidative stress alleviation, intracellular calcium signalling, and reactive compound detoxification showed rapid changes in their expression patterns in response to copper exposure. Active gliding motility was observed in response to copper addition, and copper exposure decreased intracellular calcium concentration. These findings enhance our understanding of the environmental adaptation of diatoms, and elucidate the molecular basis of toxicity of chemical compounds in algae.

Our environmental DNA analysis identified Annamia-like operational taxonomic units (OTUs) from Lake Kasumigaura, Japan every summer season during the period from June 2012-May 2015. A strain from Lake Kasumigaura that agreed with an Annamia-like OTU (NIES-4383) was established with a cell-sorting machine. Based on the differences in morphology and 16S rRNA sequences, a new taxon is described: Annamia dubia Tuji, Yamaguchi et Niiyama sp. nov. A. dubia produces a microcystins that is also produced by A. toxica. Our 16S rRNA phylogenetical analysis reveals that the genus Annamia makes a monophyletic clade with the genera Geminocystis, Geminobacterium, and 'Cyanobacterium.' Although this clade agrees with Cyanobacteriaceae Komarek et al. (2014), this family is invalid based on the invalid genus Cyanobacterium and the type species Cyanobacterium stanieri. We propose the alternative name Geminocystaceae Tuji, Yamaguchi et Niiyama fam. nov. based on the genus Geminocystis.

Nitzschia taikiensis sp. nov. is a brackish diatom species found in the Toberi River marsh, eastern Hokkaido, Japan. This species has characteristics similar to Nitzschia subamphioxoides Hustedt, which was originally described by Hustedt in 1959. In the present study, we conducted a comparative morphological analysis of N. taikiensis and N. subamphioxoides. The obtained results showed that they are different species. Sampling sites of N. taikiensis were located in salt marsh environments with very low salinity (1-5‰), acidic pH (5.2-5.9) and high mud content (95.0-97.5%). Identification of this species was relatively easy based on LM and SEM image analysis of its frustule features, such as the external form and stria density. This species has not been previously reported in Japan, which could be attributed to the reduction or loss of Japanese freshwater and salt marsh environments in the coastal areas, resulting from urban and industrial development.

The phylogenetic affiliation of Oroscenidae, a family of Radiolaria possessing large siliceous skeletons, was thoroughly revised in this study. Plankton sampling was conducted over seven years in seven sea areas of the Northern Hemisphere. Molecular analyses on the obtained specimens revealed that living oroscenids are phylogenetically different from hitherto-known radiolarian orders. The detailed examinations by Microfocus X-ray Computed Tomography and Scanning Electron Microscopy clarified that oroscenids and the related family (Thalassothamnidae) have unique skeletal characteristics different from other radiolarian orders. Judging from their phylogenetic distinctiveness and the difference in the morphology and ecology, Oroscenidae and Thalassothamnidae should be classified in a single order distinct from other radiolarian orders, and consequently, a new order, Orodaria, is established.

For decades, it has been unclear as to how the world's first cities, in southern Mesopotamia, not only arose in a fluvial environment but also how this environment changed. This paper seeks to understand the long-term fluvial history of the region around Uruk, a major early city, in relation to water-human interactions. This paper applies geomorphological, historical and archaeological approaches and reveals that the Uruk region in southern Mesopotamia had been under the influence of freshwater fluvial environment since the early Holocene. It further demonstrates how canals and long-term human activities since the mid Holocene have been superimposed on the natural river channel patterns. Fieldwork has been conducted to ground-truth features identified applying remote sensing techniques. Five sediment cores were analysed to elucidate palaeoenvironmental changes. Radiocarbon ages for organic samples suggest that the oldest sediment layers, at a depth of 12.5 m, are from the Early Holocene, while results from diatom analyses imply that the whole sediment column was deposited in a freshwater environment. Intensive networks of palaeochannels and archaeological sites within the study area have been reconstructed and these networks have been divided into four different time intervals based on changes in channel courses. The first is from the early 4th to the late 1st millennium BCE; the second is from the late 1st millennium BCE to the middle 2nd millennium CE; the third lasted from after the Islamic period until the 1980s; the fourth is from the 1980s until the present. Key results include evidence for freshwater environments and favourable settlement conditions had already formed by the 8th millennium BCE. The favourable settlement environment resulted in stable (long-lived) canals between the 4th millennium BCE and 1st millennium CE. A significant settlement and irrigation expansion occurred in the early 1st millennium CE. Major abandonment ensued in the late 1st millennium CE and lasted until the mid 2nd millennium CE.

To study the photosynthetic associations of modern radiolarians, we analyzed plankton samples from waters shallower than 200 m at 30 stations in the western North Pacific. A total of 328 taxa, including morphotypes, were identified from 2091 specimens. The fluorescence patterns under an epifluorescence microscope were mainly classified into five groups: 1) RD 2) R-G; 3) Y-B; 4) Periph-R; and 5) Pale-R. There were 37 species/morphotypes with the RD 2) facultative associations; and 3) non-associations. Many taxa belonging to Acanthodesmiidae and Lophospyris have a great number of symbiotic dinoflagellates outside the central capsule. However, the Acanthodesmiidae includes non-photosynthetic holobionts (Amphispyris and Ceratobotrys borealis), suggesting different environmental adaptability in some acanthodesmiid species. In contrast with the obligate symbiosis tendency in Acanthodesmiidae, the Lophophaenidae tends to have non-photosynthetic holobionts. In Spumellaria, one significant tendency was recognized in Tetrapyle and Phorticium as obligate dinoflagellate holobionts. Thus, Tetrapyle and Phorticium are useful for tracing oceanographic conditions in the euphotic zone. Dictyocoryne truncata and D. profunda are classified into the R-G pattern, whereas D. muelleri was grouped into the R&D pattern, indicating that the difference in the photosynthetic association may be closely related to the dwelling depth. The Q-mode cluster analysis showed that the 30 stations were classified into four clusters: A1, A2, B, and C. The geographical distributions of the four cluster groups are consistent with the climate zone and water masses, suggesting that the species composition of these shallow taxa is influenced by the distribution of water masses. In particular, the Kuroshio Current may play an important role in the migration of shallow living radiolarian species from the subtropical climatic zone to the subarctic climatic zone.

Experimental culture studies of living radiolarians experience many difficulties because radiolarians are too sensitive to be maintained alive in artificial conditions. We here developed an improved experimental protocol in order to detect newly-formed parts of the polycystine radiolarian skeletons after they were labeled with fluorescent markers. Living samples were collected from surface seawater of the Kuroshio Current offshore from Kashiwajima Island, Kochi Prefecture on the island of Shikoku, Japan. The taxonomic composition of the Kashiwajima radiolarian samples varied markedly across the seasons and sampling sites. Spumellaria were usually abundant in samples collected near Kashiwajima, and had high diversity in shell morphology. Here, we performed experimental studies on living spumellarian radiolarians to clarify their siliceous skeletogenesis. Our culture-based research on spumellarians provided the following results. (A) The pattern of silica deposition on the skeleton of Spongaster tetras tetras varies depending on the growth stage. Three ontogenetic stages were identified: (1) young, (2) progressively-growing and (3) fully-grown. Furthermore, novel varied types of skeletal growth modes were determined as follows: (i) rapid growth on the outermost shell with enlargement of shell size and (ii) internal deposition on skeletal components without change in shell size. From measurements of the growth rate of cultured radiolarians, it is assumed that S. tetras tetras cell has at least a month-long life cycle. (B) Spherical spumellarians have their own shell-forming strategy that permits additional silicogenesis while maintaining the taxonomically-specific shape of their shell; the meshwork of their shell surface consists of polygonal-shaped pore-frames formed by heterogeneous patterns of added silica. Our direct observation with fluorescence markers detected a skeletogenesis process of Haliommilla capillacea possessing a fragile spherical shell. We thus confirm the bridge-growth hypothesis for morphogenesis of the polygonal frame as proposed in previous studies. Spongosphaera streptacantha, having extremely long spines, exhibited a special growth pattern of spine elongation in a centrifugal direction, without a change in width. This was achieved by a particular temporal pattern of silicification characterized by an alternating pattern of patchy addition of new silica on the entire part of each blade from the base to the tip. Moreover, a thin layer of new silica was added by a flowing deposition along the edge of the spine. Based on these culture-based studies using living radiolarians, we conclude that Spumellaria control and maintain a particular shell shape by regulating where silicification takes place on the skeleton, particularly depending on the growth stage.

Nasty smell of tap water supplied from Lake Biwa caused a great trouble. Then many researches have been conducted from the point of view of water supply management or water quality in Japan. The matter of this bad smell was identified as 2-methylisoborneol (2-MIB) and the source organism of this bad odor was then reported as Phormidium tenue and later two different cultured strains were established. One of these strains shows green color, produce 2-MIB, and is marked PTG. The other shows brown color, does not produce 2-MIB and is marked PTB. However their nomenclatural description has not been done yet and, in fact, they have morphological characters of genus Pseudanabaena rather than Phormidium. Pseudanabaena species are also observed in Lake Kasumigaura. PS1306 produces 2-MIB and other strain PS1303 has no smell. This study focuses on morphological and genetical (16S rRNA) comparison of strains from both lakes. In addition, the ultrastructure of cells of PTB and PTG are demonstrated. On the basis of this comparison we propose description of two new planktic species producing 2-MIB: Pseudanabaena foetida Niiyama, Tuji et Ichise sp. nov. and P. subfoetida Niiyama et Tuji sp. nov.

Cross-sections were prepared by ultramicrotome (UM) and focused ion beam (FIB) system in order to examine the skeletal structure of ecologically and geologically important shell-bearing protists: phaeodarians and radiolarians. The elemental composition of the skeleton was clarified by the energy dispersive X-ray spectroscopy, suggesting that the skeletons of both groups are mainly made of amorphous silica (SiO2·nH2O) with other minor elements (Na, Mg, Al, Cl, K, Ca and Fe) and that these two groups have similar elemental composition, compared with other siliceous organisms (diatoms and sponges). However, the structural difference among the two groups was confirmed: phaeodarian skeletons are porous, unlike radiolarians with solid skeletons. It was also revealed that the phaeodarian skeleton contains concentric layered structure with spaces, presumably related to the ontogenetic skeleton formation. The distinction in the skeletal ultrafine structure (porous/solid and non-dense/dense) would reflect the ecological difference among the two groups and could be an effective criterion to determine whether microfossils belong to Radiolaria or Phaeodaria. The UM and FIB combined method presented in this study could be a useful approach to examine the chemical and structural characteristics of unculturable and/or rare microorganisms.

In a previous publication, we provided details on the typification of Fragilaria subconstricta Ostrup and Fragilaria tenuistriata Ostrup (Tuji & Williams 2008). We inadvertently switched our reprod...

A phaeodarian morphotype, characterized by the feet surrounded with forked pedal spines with anchor-like structures, was collected in the subtropical North Pacific. Considering the morphological and phylogenetic uniqueness, this morphotype is described as Gazelletta kashiwaensis sp. nov. The distribution of this new species is possibly affected by the Kuroshio Current. The feeding behavior of living phaeodarians was first filmed: the present new species floated in the water column stretching "protoplasmic webs" and collected diatoms by repeating the expansion and retraction of "pseudopodium-like tentacles".

The secretion process of the siliceous skeleton in polycystine radiolarians has drawn a great deal of interest during the last century; however, little is known about the actual physiological process of silica deposition. Recently, the PDMPO (2-(4-pyridyl)-5-[(4-(2-dimethylaminoethylaminocarbamoyl) methoxy)-phenyl] oxazole) method for staining silica deposition sites in polycystines was developed. In the present study we examined over 30 polycystine cells with PDMPO and found that both the skeletons and pseudopodia of three species (Lithelius sp., Rhizosphaera trigonacantha and Arachnosphaera hexasphaera) were stained and emitted green fluorescent light. Staining of the skeleton was probably the result of skeletal thickening growth, whereas staining of the pseudopodia may indicate that siliceous matter is assimilated within pseudopodia. We refer to this hypothesis as the ‘pseudopodial silica absorption hypothesis’ (PSA hypothesis). If this hypothesis is correct, PSA is an intermittent process, and the absorbed silica within pseudopodia is quickly transferred to the cytokalymma where it is deposited on the skeleton. To date, the PSA process has been observed in only the three species cited above; therefore we are unable to evaluate whether the PSA process is unique to these species or a common process that occurs in all polycystines; further investigation is necessary.

Seagrasses are known to have allelopathic activity to reduce growth of phytoplankton. We found growth-inhibiting bacteria (strains E8 and E9) from Zostera marina possessing strong activity against the toxic dinoflagellate Alexandrium tamarense. Strain E9 markedly inhibited growth of A. tamarense even with initial inoculum size as small as 2.9 cells ml(-1). This bacterium also had growth-inhibiting effects on the red-tide raphidophytes Chattonella antiqua and Heterosigma akashiwo, the dinoflagellate Heterocapsa circularisquama, and the diatom Chaetoceros mitra. Small subunit (SSU) ribosomal DNA (rDNA) sequencing analysis demonstrated that the most probable affiliation of these strains was Flavobacteriaceae, and proved that another inhibitory bacterial strain (E8) was the same species as strain E9. Two other bacterial strains (E4-2 and E10), showing different colony color and isolated from the same seagrass sample, revealed no growth-inhibiting activity. Interestingly, strain E4-2 showed the same sequences as E8 and E9 (100 %), and strain E10 matched E8 and E9 with 99.80 % similarity. Growth-inhibiting bacteria against the toxic dinoflagellate Alexandrium tamarense associated with seagrass, such as Flavobacterium spp. E8 and E9, are able to repress shellfish poisoning besides the allelopathic activity of seagrass itself.

In order to observe the silicification process of polycystine radiolarians, we tried to culture Streblacantha cf. circumtexta with the addition of dissolved silica (final concentration 10 μM) and f/2 culture medium from 25th, Nov. to 27th, Nov., 2009. During our session of observation, one cell of S. cf. circumtexta (Pylonioidea, Spumellaria) formed siliceous fragments in the extracapsulum part of the protoplasm, which were subsequently ejected. A total of 94 siliceous fragments were thus expelled from the cell by using the low-contrast thin (LCT) pseudopodia. Similar siliceous fragments were often found in the extracapsulum of many pylonioid spumellarians, suggesting they did also secret isolated siliceous fragments. Pylonioids may silicify continuously, and the normal growth rate of the siliceous skeleton is maintained by the disposal activity of excess silification.

Zooplankton samples from the deep water of the Sea of Japan often contain yellowish semitransparent spheres (1.0–1.5 mm in diameter). We recognized these spheres as a single phaeodarian species (Cercozoa, Rhizaria) and described them as Aulographis japonica sp. nov. (family Aulacanthidae) in this paper. This species has a high abundance in the Japan Sea Proper Water (JSPW) and occasionally higher biomass than that of copepods. Molecular analysis based on 18S SSU rDNA revealed that Aulacantha scolymantha, which belongs to the same family as A. japonica, is closer to Aulosphaera trigonopa and Protocystis spp., which belong to different orders, than to the present species. The distribution of A. japonica is apparently restricted to low temperature water. Its biomass was the highest in the uppermost layer of JSPW, and this phaeodarian species was the second most important zooplankton below 250 m depth in terms of biomass among the total zooplankton groups. This is probably due to its generalist type of feeding. Considering its large biomass, A. japonica possibly plays an important role in matter cycles within the Sea of Japan.

The field of microbiology was established in the 17th century upon the discovery of microorganisms by Antonie van Leeuwenhoek using a single-lens microscope. Now, the detailed ultrastructures of microorganisms can be elucidated in situ using three-dimensional electron microscopy. Since the availability of electron microscopy, the taxonomy of microscopic organisms has entered a new era. Here, we established a new taxonomic system of the primitive algal genus Glaucocystis (Glaucophyta) using a new-generation electron microscopic methodology: ultra-high-voltage electron microscopy (UHVEM) and field-emission scanning electron microscopy (FE-SEM). Various globally distributed Glaucocystis strains were delineated into six species, based on differences in in situ ultrastructural features of the protoplast periphery under UHVEM tomography and in the mother cell wall by FE-SEM, as well as differences in the light microscopic characteristics and molecular phylogenetic results. The present work on Glaucocystis provides a model case of new-generation taxonomy.

Umezakia natans M.Watan. was described by Dr. M. Watanabe in 1987 as a new species in the family of Stigonemataceae, following the rules of the Botanical Code. According to the original description, this planktonic filamentous species grows well in a growth media with pH being 7 to 9, and with a smaller proportion of sea water. Both heterocytes and akinetes were observed, as well as true branches developing perpendicular to the original trichomes in cultures older than one month. Watanabe concluded that Umezakia was a monotypic and only planktonic genus belonging to the family of Stigonemataceae. Unfortunately, the type culture has been lost. In 2008, we successfully isolated a new strain of Umezakia natans from a sample collected from Lake Suga. This lake is situated very close to the type locality, Lake Mikata in Fukui Prefecture, Japan. We examined the morphology of this U. natans strain, and conducted a DNA analysis using 16S rDNA regions. Morphological characters of the newly isolated strain were in a good agreement with the original description of U. natans. Furthermore, results of the DNA analysis showed that U. natans appeared in a cluster containing Aphanizomenon ovalisporum and Anabaena bergii. Therefore we conclude that Umezakia natans belongs to the family of Nostocaceae, not to Stigonemataceae.

To understand the characteristics of the ecosystem in Japanese lowland marsh, we investigated chlorophyll-a (Chl. a), photosynthesis and respiration of a phytoplankton community in a brownish-colored pond in Naka-ikemi marsh, Tsuruga, Fukui Prefecture. Chl. a concentrations and volumetric gross primary production rates ranged between 1.3–57.0 μg Chl. a l−1 and 148–1619 μg C l−1 day−1 during the study period. Higher values of Chl. a and primary production rates were clearly observed from June to September, when the dominant algae were the phytoflagellates, Peridinium (Dinophyceae) and Cryptomonas (Cryptophyceae), with swimming ability. The trophic status of the pond water of Naka-ikemi marsh was defined as being in eutrophic condition based on the biomass and productivity of phytoplankton. However, depths of Z 1% showing the productive layer in this study site were relatively narrower than those observed in the hyper-eutrophic Lake Suwa with frequent cyanobacterial water bloom. Factor-attenuating underwater light intensity in Naka-ikemi marsh was presumed to be colored dissolved organic matter. Thus, not only phytoplankton primary production, but also allochthonous organic matter supplied from the catchment area seems to be the dominant factor in the whole energy budget of the pond. In conclusion, we regarded the pond ecosystem in Naka-ikemi marsh to be in a eutrophic–dystrophic condition.

2-(4-pyridyl)-5-[(4-(2-dimethylaminoethylaminocarbamoyl)methoxy)-phenyl] oxazole (PDMPO) is a fluorescent compound that accumulates in acidic cell compartments. PDMPO is accumulated with silica under acidic conditions, and the newly developed silica skeletons show green fluorescent light. This study is the first to use PDMPO in polycystine radiolarians, which are unicellular planktonic protists. We tested Acanthodesmia sp., Rhizosphaera trigonacantha, and Spirocyrtis scalaris for emission of green fluorescence. Entire skeletons of Acanthodesmia sp. and Sr. scalaris emitted green fluorescent light, whereas only the outermost shell and radial spines of Rz. trigonacantha showed fluorescence. Two additional species, Spongaster tetras tetras and Rhopalastrum elegans did not show fluorescence. Green fluorescence of the entire skeleton is more like the “skeletal thickening growth” defined by silica deposition throughout the surface of the existing skeleton. The brightness of the fluorescence varied with each cell. This difference in fluorescence may reflect the rate of growth in these cells. Green fluorescence in PDMPO-treated polycystines suggests the presence of similar metabolic systems with controlled pH. The results of this study shed light not only on the feasibility of using PDMPO in diatoms and siliceous sponges, but also in polycystines. Further application of PDMPO could refine polycystine skeletogenic hypotheses and offer new insight on the physiological functions of silica assimilation.

Fragilaria mesolepta Rabenh. was first described by Ludwig Gottlob Rabenhorst on the label to no. 1041 of his exsiccata, Die Algen Europas. The label provides collection information in addition to a description of the species and is accompanied by a small sheet with two figures. Among the various sets of the exsiccata that were distributed, the specimens in packets labeled 1041 were found to include diatoms with three different morphologies. Only specimens of one of these morphologies conform to the illustration and description given by Rabenhorst. We designate as lectotype of F. mesolepta an individual on slide 3616 in the Farlow Herbarium. We also examined the type material of Fragilaria subconstricta Ostrup and Fragilaria tenuistriata Ostrup, which were considered synonyms of F. mesolepta by Lange-Bertalot in Krammer & Lange-Bertalot (1991). Both taxa are not synonyms of F. mesolepta, but different species and can be identified using shape and position of a rimoportula.

SUMMARY Fragilaria rumpens (Kutz.) G. W. F. Carlson is assumed to be a cosmopolitan species, and is often reported from ponds and lakes. Nevertheless, this species is similar to both Fragilaria capucina Desm. and Fragilaria vaucheriae (Kutz.) J. B. Petersen and, as a consequence, the taxonomy of all three species has been confusing. In an attempt to solve the taxonomic problems within this group, we have examined the type material of Synedra rumpens and discuss the differences between it and some of those species said to be similar.

The application of the generic name Fragilaria has remained uncertain because the identity of the lectotype, Conferva pectinalis O. F. Mull., is unknown. Traditionally Fragilaria capucina Desm. has been considered a synonym of F. pectinalis, although this synonymy has not been confirmed. Application of the generic name Fragilaria can best be fixed by designating an epitype for C. pectinalis that fits the current circumscription of the genus (sensu Williams & Round). As epitype for C. pectinalis, we designate a specimen that Dillwyn thought to be representative of that species. We also examined the type material of F. capucina. Specimens from this material have a rimoportula at each pole and open girdle bands. Although the first character was not part of the revised definition proposed by Williams & Round, F. capucina can be placed in Fragilaria on account of the structure of its striae and the general appearance of the basal siliceous layer. Fragilaria capucina is, however, clearly not a synonym of F. pectinalis.

The horizontal distribution of dissolved oxygen (DO) concentrations on the lake bottom was investigated on September 2-5, 2002. At 36 out of the 84 sites, DO concentrations were at less than 50% of saturation. The biomass of macrophytes was investigated on September 6- 11 at 44 sites, and ignition loss of sediments was investigated at 41 sites on September 17-18. The results of multiple regression analysis suggested that DO concentrations could be estimated using the biomass of Egeria densa, Myriophyllum spicatum, and Potamogeton maackianus, and the water depth as explanatory variables (R = 0.65, R' = O.61, n = 44, P 0.01). Both the partial correlation coefficient and partial regression coefficient indicated that biomass of Egeria densa was the most influential environmental factor on the fluctuation of DO concentrations on the bottom water.

International audience; Phaeodarians are a group of widely distributed marine cercozoans. These plankton organisms can exhibit a large biomass in the environment and are supposed to play an important role in marine ecosystems and in material cycles in the ocean. Accurate knowledge of phaeodarian classification is thus necessary to better understand marine biology, however, phylogenetic information on Phaeodaria is limited. The present study analyzed 18S rDNA sequences encompassing all existing phaeodarian orders, to clarify their phylogenetic relationships and improve their taxonomic classification. The monophyly of Phaeodaria was confirmed and strongly supported by phylogenetic analysis with a larger data set than in previous studies. The phaeodarian clade contained 11 subclades which generally did not correspond to the families and orders of the current classification system. Two families (Challengeriidae and Aulosphaeridae) and two orders (Phaeogromida and Phaeocalpida) are possibly polyphyletic or paraphyletic, and consequently the classification needs to be revised at both the family and order levels by integrative taxonomy approaches. Two morphological criteria, 1) the scleracoma type and 2) its surface structure, could be useful markers at the family level. (C) 2015 Elsevier GmbH. All rights reserved.

International audience; Symbiotic interactions between pelagic hosts and microalgae have received little attention, although they are widespread in the photic layer of the world ocean, where they play a fundamental role in the ecology of the planktonic ecosystem. Polycystine radiolarians (including the orders Spumellaria, Collodaria and Nassellaria) are planktonic heterotrophic protists that are widely distributed and often abundant in the ocean. Many polycystines host symbiotic microalgae within their cytoplasm, mostly thought to be the dinoflagellate Scrippsiella nutricula, a species originally described by Karl Brandt in the late nineteenth century as Zooxanthella nutricula. The free-living stage of this dinoflagellate has never been characterized in terms of morphology and thecal plate tabulation. We examined morphological characters and sequenced conservative ribosomal markers of clonal cultures of the free-living stage of symbiotic dinoflagellates isolated from radiolarian hosts from the three polycystine orders. In addition, we sequenced symbiont genes directly from several polycystine-symbiont holobiont specimens from different oceanic regions. Thecal plate arrangement of the free-living stage does not match that of Scrippsiella or related genera, and LSU and SSU rDNA-based molecular phylogenies place these symbionts in a distinct clade within the Peridiniales. Both phylogenetic analyses and the comparison of morphological features of culture strains with those reported for other closely related species support the erection of a new genus that we name Brandtodinium gen. nov. and the recombination of S. nutricula as B. nutricula comb. nov.

1995年8月に琵琶湖北湖の沿岸帯において,糸状緑Spirogyra sp.が優占する付着藻群落内の溶存酸素濃度の日変化を調べた。Spirogyra群落内は18:00から20:00にかけて濃度が5mg l-1から2.3mg l-1に半減した。その状態は翌日4:00まで続き,Spirogyra群落内では夜間に溶存酸素濃度が明確に減少する傾向が観察された。糸状緑藻群落内の溶存酸素濃度の低下は,他の生物に対して,生息環境の悪化を引き起こしている可能性が考えられた。

Juttner I., Krammer K., Van de Vijver B., Tuji A., Simkhada B., Gurung S., Sharma S., Sharma C. and Cox E.J. 2010. Oricymba (Cymbellales, Bacillariophyceae), a new cymbelloid genus and three new species from the Nepalese Himalaya. Phycologia 49: 407–423. DOI: 10.2216/09-77.1 A new genus Oricymba is described with its type species based on Cymbella japonica Reichelt. In addition, three new species are described from the Nepalese Himalaya: O. subaequalis, O. latirotundata and O. subovalis. The new genus has slightly dorsiventral or almost symmetrical valves with polar raphe endings deflected to the dorsal side. It can be distinguished from other cymbelloid genera by two morphological characters. There is a ridge along the valve face: mantle junction, and areolae are slit-like and partially occluded by dentate projections. To date Oricymba has been found only in often nutrient-poor, freshwater habitats of the Indian subcontinent, Southeast Asia, Korea and Japan.

The growth rates of 12 strains of attached freshwater diatoms were examined as a function of irradiance. The results were used to determine physiological parameters in the growth-irradiance relationships. Values of Gmax (maximum growth rate) and I k (irradiance at half of Gmax ) correlated with successional phase. The development of attached diatom communities appears to proceed from high irradiance species to low irradiance species that appear later in the successional sequence. Thus, efficiency of light use is linked to successional strategy, as has been documented for terrestrial plants.