We describe a new genus of monoraphid diatom based on Achnanthidium ovatum T.Watanabe et Tuji in Watanabe et al., a species described originally from Japan. We encountered this species from Yunnan Province in the southwestern part to eastern China, as well as in Luding, Sichuan Province and Xianju, Zhejiang Province, in pristine lotic environments. The species differs from the genus Achnanthidium by being asymmetrical to the transapical axis and has a pseudoseptum at the poles of the interior of the raphe valve which is fused with each helictoglossa. Moreover, a distinct group of condensed striae can be found at the narrower pole ('footpole') of the raphe valve. This appears to be the only known genus of freshwater monoraphid diatoms that is restricted to a single continent.

During a survey on freshwater epilithic diatoms from subtropical lotic environments belonging to the Cascavel River microbasin, Paraná State, Brazil, we observed populations of a new Nupela Vyverman et Compère species. Morphological and meristic analyses were performed using light and scanning electron microscopy, resulting in the description of Nupela semifasciata sp. nov. This species is characterized by elliptic-lanceolate valves containing subcapitate apices in larger individuals and broadly rostrate-rounded apices in smaller ones, while the length/width ratio gradually decreases as the individuals become smaller. The central area unilaterally reaches the margin and always interrupts the row of areolae on the valve mantle. The valve mantle is externally composed of a second row of areolae near the apices. We cross-checked information with similar Nupela taxa, highlighting the main features that separate them. Nupela semifasciata was found in streams with acidic-neutral pH, low conductivity and low to high nutrient concentrations.

We describe valve ultrastructure of two species of the freshwater diatom genus Gomphonema from a stream and Lugu Lake in Yunnan Province, China, and describe one of these two species as new to Science. Gomphonema emines Skuja was described over 80 years ago. This large, multistigmate species has uniseriate striae without occlusions, large pseudosepta and septa, and internal stigma openings that are round, positioned within ellipsoidal depressions on the extended central nodule. In these features it is distinguished from most of the 'typical' species of the genus. Gomphonema yunnaniana Y.Liu et Kociolek sp. nov. has biseriate striae without occlusions, a large, round external stigma opening and an internal stigma opening that is elevated and contained within a lip-like structure. In these features it is distinguished from the 'typical' species of the genus. We compare these two putatively endemic species from Yunnan with other species groups of the genus.

Examination of type material for Ulnaria splendens, Ulnaria aequalis and Ulnaria obtusa provides evidence to support each as a distinct and definable taxon. None can be considered more closely related to any other species in the genus Ulnaria and are therefore all recognised at the same rank, that of species. We briefly discuss five further taxa that involve the name Synedra splendens: Synedra splendens var. marina, Synedra splendens var. salina, Synedra splendens var. brevis, Synedra splendens var. subspathulata and Synedra (ulna var.) spathulifera.

The taxonomy of coccoid cyanobacteria has been largely revised in recent years. In this study, a novel coccoid cyanobacterial strain was isolated from a watercourse at the Poyang Lake Model Research Base, Jiangxi province, Eastern China. A polyphasic approach combining morphological and molecular testing was used to characterize this strain referred to as CHAB 4018. Regarding colonial form and cellular spatial arrangement, this strain was morphologically similar to strains of the genus Eucapsis. The maximum 16S rRNA gene sequence similarity of this strain to the currently described cyanobacteria genera was 93.40%, exceeding the cutoff for genus delimitation in bacteriology. Furthermore, a phylogenetic tree based on 16S rRNA gene sequences indicated that strain CHAB 4018 formed a unique clade in the family Chroococcaceae and was phylogenetically close to the recently established genus Cryptococcum but distant from the Chroococcus 'sensu stricto' clade and from Eucapsis. Thus, a novel coccoid cyanobacterial genus with a new species is here described as Neochroococcus gongqingensis. A large phylogenetic tree using more strains suggested phylogenetic intermixture of Chroococcus-like and Eucapsis-like cyanobacteria, suggesting the need for further studies on the phylogeny and taxonomy of coccoid cyanobacteria.

The diatom genus Tabellaria Ehrenberg is one of the most widely distributed genera in freshwaters, both in benthos and phytoplankton. It is rather frequent in unpolluted, circumneutral to slightly acidic and poorly mineralized lakes, streams and peat bogs. Despite being studied intensively in the last decades, the taxonomy of this genus is still unsatisfactory as some authors recently proposed to consider most species as synonyms of Tabellaria flocculosa (Roth) Kützing. Several dozen of Tabellaria rich samples from Europe were investigated and six were selected to illustrate typical populations. Five new species are described based on detailed LM and SEM observations: Tabellaria acidodelicata sp. nov., Tabellaria hercynica sp. nov., Tabellaria koppeniana sp. nov., Tabellaria procera sp. nov. and Tabellaria valdeventricosa sp. nov. Additionally, the type materials of T. fenestrata, T. flocculosa and T. ventricosa have been investigated and illustrated together with a discussion on Tabellaria andina stat. nov., at present exclusively found in South America.

Many diatom groups are known for widespread (pseudo)cryptic species diversity and Pinnularia gibba group is one of them. Recently, Kollár et al. (2019) delimited species within the group by means of a polyphasic approach, providing an evidence for the existence of fifteen species. In order to further guide the systematic revision of the group, the present study focuses on the evolution and morphology of the P. gibba group. Using representatives of the fifteen species we used fossils to constrain and calibrate a multi-gene species-level phylogeny. Although many species are morphologically highly similar, significant differences in cell size were detected in different sections of the tree, suggestive of ongoing morphological differentiation. We further used the phylogenetic analysis to assess marker resolution for DNA barcoding, showing that the proposed diatom barcode markers rbcL and V4 SSU rDNA can distinguish closely related (pseudo)cryptic species of the group.

The identity and nomenclatural history of several small-celled naviculoid taxa are revisited. The species discussed here are important from the ecological point of view since they are often dominant in benthic freshwater communities. The original concepts of several species that have suffered major taxonomic drift due to their entangled nomenclatural history are discussed, and forgotten epithets are resurrected. We examined the original material of Navicula aggerica E. Reichardt, Navicula atomoides Grunow, N. crassulexigua E. Reichardt, N. minima Grunow, N. minima var. typica R. Ross, N. minutissima (Kütz.) Grunow, N. saugerresii Desm., N. seminulum Grunow, N. seminulum var. intermedia Hust., N. seminulum var. radiosa Hust., N. stroemii Hust., N. subbacillum Hust., N. subseminulum Hust., N. tantula Hust., N. vasta Hust., N. ventraloides Hust., Stauroneis fonticola Hust., and Synedra minutissima Kütz. Several of these names were regarded as synonyms in many floristic works and, as such, remained forgotten or ignored. Analyses using light and scanning electron microscopy indicate conspecificity of Navicula minima (= Sellaphora seminulum sensu auct. nonnull.) with Sellaphora saugerresii (Desm.) C.E. Wetzel et D.G. Mann comb. nov., which has priority against N. minima. Synedra minutissima is lectotypified and transferred to Halamphora minutissima (Kütz.) C.E. Wetzel et Compère comb. nov. Navicula minutissima (Kütz.) Grunow 1860, nom. illeg. and Navicula minima Grunow pro parte, typo excl. designate one and the same species (valid and legitimate), currently known as Sellaphora aggerica (E. Reichardt) Falasco et Ector. We consider Sellaphora atomoides (Grunow) C.E. Wetzel et Van de Vijver comb. nov. (= Eolimna tantula sensu auct. nonnull.) and Sellaphora nigri (De Not.) C.E. Wetzel et Ector comb. nov. (= Eolimna minima sensu auct. nonnull.) to be separate species, although morphologically very similar. Sellaphora crassulexigua (E. Reichardt) C.E. Wetzel et Ector comb. nov. and Sellaphora subseminulum (Hust.) C.E. Wetzel comb. nov. are rarely encountered, but usually found in calcareous springs and aerial habitats, respectively. All species are transferred to the genus Sellaphora on the basis of their valve morphology, pending molecular studies confirming the monophyly of the group once living material of each can be located and brought into clonal culture. Additionally, 64 established taxa from Navicula s.l., Eolimna or Naviculadicta are formally transferred to Sellaphora. Navicula subminuscula Manguin is formally transferred to the genus Craticula Grunow.

A new monoraphid diatom genus, Platebaikalia gen. nov., was described based on a detailed morphological investigation using light and scanning electron microscopy. Previously Platessa elegans Kulikovskiy et Lange-Bertalot was described from ancient Lake Baikal, and this species serves as the generitype for the newly-described genus. Platebaikalia elegans is a rare taxon found in the deeper parts of Lake Baikal. Platebaikalia elegans is characterized by having multiseriate striae on the raphe valves with biseriate striae on the rapheless valves, though in some specimens a short third row of areolae may be present in some striae. Morphology of striae is helpful to distinguish the genus Platebaikalia from Platessa and other monoraphid genera. Other morphological features that differentiate our new genus from other monoraphid taxa are discussed. We review the morphological data on Platessa species, and based on these data can recognize eight groups of taxa in the genus. Our analysis shows that Platessa as currently circumscribed may contain groups of species that are quite different from one another morphologically, and possibly includes taxa that could be recognized as different at the genus level. A few new combinations are suggested when taxa from the genus Platessa transferred to genera Psammothidium and Planothidium. Some problems of taxonomy of monoraphid taxa are discussed and we believe that taxonomy of this group of diatoms is in need of special attention in future.

A new freshwater diatom species, Gomphonema adhikarii sp. nov., is described from a small road-side pool from the alpine region of Arunachal Pradesh, Eastern Himalayas, India. Detailed valve morphological features, based on both light and scanning electron microscopy, is presented and this taxon is compared with similar species. Gomphonema adhikarii has a distinct asymmetry about the apical axis and slightly bent foot pole area. The outline of the valve is slightly undulate, the valve centre is swollen and both apices are broadly rounded. This new species described from the Eastern Himalayas supports the idea of the area being rich in biodiversity, even with respect to the freshwater diatom flora.

Background and Aims: "Order please!" was a recently published, very nice and apt title for a persistent problem in green algae phylogenetics. The green algal class Chlorophyceae comprises two clades (SV and OCC) made up of five orders (Sphaeropleales, Volvocales, Oedogoniales, Chaetopeltidales and Chaetophorales). A variety of data and methods have shown that one further group (Golenkinia+Jenufa) cannot be unambiguously placed among the five orders. In addition, concerning Sphaeropleaceae and/or Treubarinia the monophyly of Sphaeropleales and Volvocales remain unresolved. Methods: IUPAC (International Union of Pure and Applied Chemistry) encoded consensus sequences for different 18S rDNA data sets as well as corresponding 18S rDNA consensus structures were assembled for Sphaeropleales, Volvocales (with or without Treubarinia) and a Golenkinia+Jenufa assemblage to independently infer phylogenetic relationships in a three-taxon analysis. Using a known template structure, individual 18S rDNA secondary structures were predicted by homology modelling. Sequences and their individual secondary structures, automatically encoded by a 12-letter alphabet (each nucleotide with its three structural states, paired left, paired right, or unpaired), were simultaneously aligned; consensus structures and IUPAC encoded consensus sequences were read out from the different sequence-structure alignments. Key Results: In contrast to previous studies using 18S rDNA data, results of this study corroborate chloroplast data and strongly support a sister group relationship between Golenkinia+Jenufa and the Sphaeropleales. The Golenkinia+Jenufa assemblage shows 330 matches to the Sphaeropleales (sequence-structure consensus) but only 214 matches to the Volvocales (sequence-structure consensus). Phylogenetically informative nucleotides are highlighted and visualized in their structural context taking into account structural domains (I-IV) and hypervariable regions (V2-V9). Rooting the three-taxon scenario remains difficult because the extremely long branches of Golenkinia and Jenufa are attracted to a chosen outgroup, reducing bootstrap support in any conceivable four-taxon tree obtained by parsimony or profile-neighbor-joining analysis. Conclusions: This algal case study of 18S rDNA consensus data (IUPAC encoded sequences and consensus structures) coupled with profile distances between groups of sequences, demonstrated that a phylogenetic problem can be reduced to a three-taxon analysis.

We describe a new species of diatom, Psammodictyon taihuensis sp. nov., collected from the Taihu Basin, Jiangsu Province, China. There are several features of this diatom that suggest it should be included in the genus Psammodictyon, notably the possession of panduriform valves characterized by a longitudinal fold near the apical axis, coarsely areolate striae, and a keeled raphe system present on the valve margin. This species is distinct from others in the genus by its small size, being only 16.5-25.0 μm long and 10.0-12.5 μm wide in the central region, and with the widest valve being 10.5-13.5 μm in width. There are 8-11 distinct fibulae per 10 μm and the striae are composed of 18-22 coarse areolae per 10 μm. This is the first report of a freshwater member of the genus Psammodictyon in China, which expands the known geographical and ecological distributions of the genus and enhances our understanding of freshwater diatom diversity in China.

We describe three new Achnanthidium species, A. lacustre sp. nov., A. sublanceolatum sp. nov., and A. taipingensis sp. nov., from Taiping Lake, Anhui Province (China) based on light and scanning electron microscopy. A. lacustre sp. nov. belongs to the "A. minutissimum complex" of the genus, based on it having straight external distal raphe fissures and round to elliptical areolae. Both A. sublanceolatum sp. nov., and A. taipingensis sp. nov. belong to the "A. pyrenaicum complex" of the genus, based on them having transpically-elongated areolae and deflected external distal raphe fissures. All three species are sufficiently different from other similar species based on valve outline, shape of the axial and center areas, and striae density. These three new species are all observed in benthic collections from Taiping Lake.

A new species from Vietnam, Cryptomonas vietnamica sp. nov., is described based on morphological and molecular data. Six strains from different habitats were analyzed. Cryptomonas vietnamica is characterized by large cells up to 54 µm long, 30 µm wide and 20 µm thick, flattened in dorso-ventral plane and often twisted. Phylogenetic relationships inferred from nuclear small and large subunit ribosomal DNA sequences show that the new species forms a clade with Cryptomonas lundii, a rare taxon, described from Europe. Cryptomonas lundii is reported for the first time from Russia and second time since its initial description.

During a survey of the diatom flora attached to carapaces of loggerhead sea turtles (Caretta caretta) from the Adriatic Sea, a large population of an unknown marine achnanthoid species was observed that could not be assigned to any of the currently described monoraphid diatom genera. Detailed morphological analysis based on scanning electron microscopy observations and comparison with a large number of monoraphid genera such as Madinithidium, Scalariella, Kolbesia and Karayevia, resulted in the description of the new benthic marine genus Majewskaea gen. nov. with the newly described Majewskaea istriaca sp. nov. as generitype. The new genus is characterized by a sternum valve showing a clear recurving ridge surrounding the entire valve margin, the presence of macroareolae closed internally by perforated hymenes, separated by a longitudinal hyaline area, a well-developed sternum and vestigial raphe slits. The raphe valve has a simple straight raphe with bent terminal fissures, a very fine striation pattern composed of macroareolae cut in two by a longitudinal hyaline zone, and a very shallow mantle. The new genus is illustrated using both LM and SEM observations and compared with other resembling marine and brackish Planothidium monoraphid species.

Thirteen Planothidium species are illustrated and discussed in a detailed morphological account based on light and scanning electron microscopy analysis of modern and historic materials related to the names Planothidium rostratum (Østrup) Lange-Bertalot and Planothidium frequentissimum (Lange-Bertalot) Lange-Bertalot. Eight species from freshwater environments in Europe, Asia and South America are proposed as new. All taxa here discussed and illustrated belong to the group of species characterized by the presence of a cavum in the rapheless valve. Additional information concerning their distribution and ecology is briefly commented based on a thorough literature revision.

A novel diatom species belonging to the genus Nagumoea is described based on detailed light and scanning electron microscopy observations. The new taxon was found abundantly in several samples collected from seagrass on the southernmost coasts of Mozambique, Southern Africa. While the new species shows characters (e.g. scalariform valvocopula, fibulae of complex shape and structure) consistent with the genus description, it differs distinctly from currently known members of Nagumoea. Differences include generally larger (7-29 µm) and more slender (1.0-1.5 µm) valves with acutely rounded apices and 4-5 areolae per stria, a doubly-perforated valvocopula, and the last-formed copula with a highly regular serrated margin. Based on the current knowledge and understanding of the diatom morphology and phylogeny, Anaulus vallus Nikolaev, previously included within the genus Denticula, is transferred to the genus Nagumoea. This brings the current number of the genus members to five. Ecological preferences of Nagumoea are briefly discussed.

An interesting population of ulvacean green algae was collected from a limno-rheocrenic, thermal, mineral (chloride, sodium, sulphate) spring known as "Ain Abu Sherouf" in the Siwa Oasis, the Western Desert of Egypt. A detailed combined investigation on its morphotaxonomy, autecology, and a multilocus sequence data set including the chloroplast-encoded rbcL gene and the nuclear-encoded nrDNA SSU and ITS allowed us to identify this population as Ulva flexuosa subsp. paradoxa (syn. Ulva paradoxa, Ulvales, Chlorophyta), although the algal thalli were in average narrower than usual in this taxon. Analysis of the molecular rbcL-ITS sequencing data demonstrated a close phylogenetic relationship of the studied population to two Ulva isolates from Japan and China and their taxonomic status was further discussed. The pigment profiling confirmed chlorophylls and carotenoids typical of the Ulvaceae (lutein, α/β-carotenes, violaxanthin, and neoxanthin). Lipidomic analysis revealed the presence of the monogalactosyl diacylglycerols (MGDG), digalactosyl diacylglycerols (DGDG), sulfoquinovosyl diacylglycerols (SQDG), and diacylglyceryl N,N,N-trimethylhomoserine (DGTS) lipid classes. Presence of the plasma membrane DGTS lipids in remarkable proportion might be an adaptation to this nutrient-poor mineral spring habitat, with relatively low phosphorus values. The lower unsaturation index (UI) values of the plastidial DGDG and SQDG lipids are likely to reflect the need to maintain adequate membrane fluidity in this thermal mineral spring system. This polyphasic study not only extended our little knowledge on the distribution, autecology, and adaptive mechanisms of U. flexuosa subsp. paradoxa in the Saharan habitats of Africa, but also re-assessed and refined the taxonomic and phylogenetic affiliation of previously sampled close relatives from East Asia.

Three new freshwater diatoms are described from China's Yunnan Plateau region in sediments from Lake Fuxian. Navicula australasiatica nov. sp., Navicula perangustissima nov. spec., and Navicula turriformis nov. spec. were identified from light and scanning electron micrographs. All new species are sufficiently different from other similar species based on valve outline, shape of the axial and center areas, and stria density. These three new species are all observed in surficial sediment from Lake Fuxian and compared to morphologically similar species from the genus Navicula.

Motto: "I consider the human endeavour to discover new processes and regularities in nature, completed by requirement and satisfaction in logical arrangement of discovered facts into the objective and regular order, as a main stimulus of the noble evolution of the human society." - Albert Einstein. The problem of identification and evaluation of new described cyanobacterial taxa, particularly of the genera established after molecular sequencing, is discussed. Numerous new taxonomic units were defined according to molecular analyses in the last 20 years, but their later identification by biological community (particularly by ecologists) is often hardly possible. The molecular sequencing and evaluation must be surely a basis of the modern and future taxonomic classification, but the application of polyphasic approach to the definition of single taxa and enabling the orientation and later recognition of all described taxonomic units is quite necessary and inevitable.

During a recent floristic-taxonomic study on the algal flora, including diatoms, from the estuary of the Damietta Branch of the Nile in Egypt, an interesting epilithic diatom species belonging to the genus Seminavis (Naviculaceae) was collected and investigated using both light and scanning electron microscopy. This new diatom species shares morphologically some taxonomic diagnostic features with other related taxa such as S. insignis, S. robusta, and S. ventricosa. However, it still differs by having ventral central striae that are shorter and more or less straight in the middle of the smaller frustules to be clearly radiate in the larger ones and then become geniculate and only radiate near the poles, the central raphe endings are externally more distantly spaced than in the similar species, the elongate central nodule is internally less prominent, and the areola density is much denser. Therefore, we here describe it as Seminavis aegyptiaca sp. nov. Hydrochemical analyses revealed that S. aegyptiaca commonly inhabits typical marine, with a weak tendency towards brackish water, habitats. It was found to be tolerant to meso-eutrophic, nutrient-enriched conditions, based on the data available on seasonal concentrations of N and P compounds. These findings not only contribute to the inventory of Egyptian diatoms, but also increase our understanding of the autecology and distribution of this relatively poorly-known diatom genus.

Abstract: Massive cyanobacterial blooms frequently occur in the Uruguay River, one of the largest rivers in South America. A heterocytous morphospecies of unique morphology has been repeatedly observed in the river since 2006 in rather high abundances. This morphospecies was preliminarily reported as Anabaena spiroides and Dolichospermum cf. pseudocompactum, but its morphology does not fully correspond with the description of these species, neither with definitions of any Dolichospermum species described so far. A clonal strain designated "strain7" was isolated in 2010 from the Lower Uruguay River and thoroughly characterised from morphological and phylogenetic points of view. An establishment of D. uruguayense spec. nov. was proposed.

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.

An unidentified diatom species belonging in the genus Nitzschia isolated from samples in the Omani coastal region of the Arabian Sea is the focus of the present study. This species has been successfully cultivated in the laboratory and DNA was harvested and sequenced. Light microscopy (LM) and scanning electron microscopy (SEM) examination of the strain revealed some distinct features, of which the ultrastructure of canal raphe and the absence of central nodule are the most remarkable ones. In terms of morphology, the strain being studied resembles taxa belonging in Nitzschia sect. Lanceolatae. However, our phylogenetic tree based on a three-gene dataset, comprising concatenated nuclear-encoded small-subunit ribosomal DNAs (SSU) and chloroplast encoded (rbcL and psbC) shows that our strain is sister to N. filiformis, which belongs in Nitzschia sect. Obtusae. This species that we have named Nitzschia omanensis, is thus far only known from the harsh coastal waters of Oman, which are characterized by very high daily temperatures and extremely low precipitation.

During a survey of the freshwater diatom flora on the sub-Antarctic islands of the southern Indian Ocean, two new Planothidium species were observed, showing some resemblance to Planothidium delicatulum. Therefore, the type material of Achnanthidium delicatulum Kützing was analysed, a common species in northern hemisphere waterbodies that was later transferred to the genus Planothidium. Additionally the material of Types du Synopsis des Diatomées de Belgique n° 234, designated in 1980 as neotype for Achnanthes delicatula was investigated. This analysis showed that the population in Types n° 234 is not conspecific with Achnanthidium delicatulum but in fact is a population of Planothidium galaicum. Both Planothidium species in the investigated Antarctic material are described as new to science: P. lilianeanum Van de Vijver sp. nov. and P. australodelicatulum Van de Vijver, C.E.Wetzel et Ector sp. nov. The new species can be differentiated based on differences in valve outline, presence of ridges and silica outgrowths on the rapheless valve, the structure of the raphe and the shape and size of the central area. Notes on the ecology and distribution of the new Antarctic species are added. Achnanthidium delicatulum is formally lectotypified.

Tropical regions are considered hotspots of biodiversity, and the genus Stigonema has been underexplored in all world, mainly due to the difficulties of culturing. In this study, we sequenced the 16S rRNA gene of a natural Stigonema population from the tropical Atlantic Rainforest (São Paulo, Brazil) and describe S. jureiensis sp. nov. based on phylogenetic and morphological data. For the molecular analysis, the genomic DNA was isolated from aliquots of the population, which were previously manually cleaned under a microscope, using a point-tapered Pasteur pipette to remove other organisms and debris. For morphological analysis, 30 individuals were analyzed and photographed using microscope. Both maximum likelihood and Bayesian phylogenies support S. jureiensis as a new species, and morphological analysis revealed the presence of a special type of mosaic ornate sheaths.

Dinoflagellate taxonomy has been undergoing a comprehensive review in recent decades. Knowledge on Brazilian dinoflagellate flora remains quite incomplete, particularly regarding the size of the country. This study is the first taxonomic survey of freshwater dinoflagellates in the State of Paraná, southern Brazil. Forty-one freshwater environments were sampled in Paraná and two others on the border between Paraná and Santa Catarina during 2010-2015, and 21 dinoflagellate taxa assigned to 13 genera were identified and described based on light (LM) and scanning electron (SEM) microscopy. A new combination is proposed: Parvodinium africanum var. javanicum comb. nov. Three taxa are new records for Brazilian freshwaters: Glenodiniopsis uliginosa, P. africanum var. javanicum and Tyrannodinium edax. Taxonomic and nomenclatural comments about the recorded species as well as their known distribution in Brazil are also given.

The marine diatom Olifantiella Riaux-Gobin et Compère predominantly occurs in tropical Indo-Pacific coral reef environments. The genus has about a dozen validly published taxa and is characterized by transapically elongate striae composed of a macroareola, broad perforated girdle, and tubular buciniportula process of trumpet-shape. The valve mantle of taxa related to the generitype, O. mascarenica, have a canal-shaped structure around the valve at the face / mantle junction, while those to O. gorandiana have a simple mantle or strongly narrow canal and complex buciniportula composed of hollow processes. The geographic distribution of Olifantiella is expanded in this study to include species observed in loggerhead sea turtles scrapes from the Aegean Turkish coast and samples from the Turkish Black Sea and Adriatic Sea coasts. Olifantiella has also been identified in Martinique Island, Caribbean Sea. A transfer of Navicula infirmitata is proposed due to the areola and buciniportula structure, as Olifantiella infirmitata. Further, an application of the Focused Ion Beam (FIB) to a sequential cutting of frustules allows resolution of Olifantiella mascarenica valve ultrastructure.

Three new subaerial species of Achnanthidium are examined and described from a karst landform of central-south China based on light and scanning electron microscopy observations, and are compared with similar taxa worldwide. A. mediolanceolatum sp. nov. is elliptical-lanceolate, not linear-lanceolate as is more typical in this genus, as well as having a bow-tie shaped central area on the raphe valve and a large lanceolate axial area on the rapheless valve, features which together make it easy to distinguish this species from others. A. parvulum sp. nov. and A. guizhouensis sp. nov. are linear-elliptical in shape, which is more common for Achnanthidium and they differ from other species mainly in size, raphe, density of striae and shape of the central area. We compared these three new species with morphologically-similar taxa, and present their ecological settings and distributions as well. The relationship between Achnanthidium and Psammothidium is discussed, and the data from these new species from Guizhou presented herein suggest the two genera are difficult to separate.

During a survey of the freshwater aquatic diatom flora of two peat bog areas in Tierra del Fuego, southern Argentina, six taxa belonging to the genus Frustulia that could not be identified were observed. Comparison with the type material of Frustulia (Navicula) crassinervia separated the Tierra del Fuego populations showing some resemblance as a new species: F. australocrassinervia sp. nov. The other five taxa are likewise described as new based on light and scanning electron microscopy observations and comparison with all known Frustulia species worldwide. Frustulia delicatula sp. nov., F. ellipticolanceolata sp. nov., F. fuegiana sp. nov., F. patagonica sp. nov. and F. yaganiana sp. nov. Comments are made on their taxonomic position and how they can be distinguished from other Frustulia species in this genus. Brief notes on the ecology and distribution of the seven taxa are added.