During recent investigations on the diatom and algal flora from the Aras Dam, northwestern Iran, an interesting epilithic diatom species belonging to the genus Nitzschia was collected and exa­mined using both light and scanning electron microscopy. This diatom species shares morphological and taxonomic features with Nitzschia clausii, N. kurzeana, N. filiformis, N. obtusa, N. lowei, and N. potapovae; however, the taxon possesses narrow, elongate frustules that are weakly sigmoid in both valve and girdle views. The sigmoid character shows itself mostly at the apex of the valve and sometimes results in a rhomboid-like appearance; it is less clear in valve view and becomes weaker in the largest frustules, which are nearly symmetrical along the apical, transapical, and pervalvar axes. Valve ends are acutely rounded and blunt, but in shorter and more sigmoid valves, they become pointed to nearly triangular. Morphology and comparison with related taxa suggests the Aras Dam species is new and here described as Nitzschia arasensis Atazadeh, Ghavam et Edlund sp. nov. Water chemistry in the Aras Dam suggests that N. arasensis inhabits fresh to slightly brackish water.

Aulacoseira Thwaites is one of the oldest known diatom genera to inhabit freshwater ecosystems, having been recorded from multiple localities from the late Cretaceous. The genus continued to evolve throughout the Cenozoic and today continues to thrive in aquatic environments globally, often forming an important contributor to phytoplankton communities. Morphological characters that define Aulacoseira had largely evolved by the Eocene, and many additional species have been uncovered since that time, especially in the Miocene. The Virgin Valley Formation, located in the northwestern portion of Nevada, USA, represents an extensive deposit that dates to middle Miocene (~14.4 Ma) and spans a period of time that covers the end of the Middle Miocene Climatic Optimum (MMCO) and onset of the Middle Miocene Climatic Transition (MMCT). The formation contains strata consisting of organic lignite, mudstones and diatomite, ranging in thickness from a few cm to tens of meters. During an investigation of the biological remains, Aulacoseira was found to dominate many of the strata, indicating the importance of this diatom in these ancient aquatic ecosystems. The objective of this communication is to provide a detailed accounting of the most common Aulacoseira species found at the Virgin Valley locality, including the descriptions of six new species. Collectively, the new taxa represent a wide range of morphological characters, and their remains are used to infer aspects of the paleoecology of the ancient habitats.

A revision of the genus Stauroforma is proposed based on the analysis of several historic slides prepared by Grunow to describe Fragilaria virescens var. exigua. The original materials are analysed using both light and scanning electron microscopy together with a critical examination of the original drawings and notes Grunow made on his new taxa. Based on this, the genus description of Stauroforma is emended and the morphological descriptions of S. exiguiformis and S. inermis are updated. Grunow's variety subsalina is raised to species level as Stauroforma subsalina. A new species, Stauroforma subcassubica is described splitting it from S. cassubica, the latter having larger valves. The results of this revision will enable a more exact identification of the different Stauroforma species observed in freshwater and brackish water bodies in Europe.

Karst rivers in Croatia are common phenomena and known biodiversity hotspots for many different groups of organisms. Due their importance from a natural, cultural and socio-economic point of view, most of them are protected as National Parks. Diatoms in these habitats are not well known, and recently detailed study has been started. During observations of samples from Lake Visovac on Krka River, one Aneumastus species with specific morphological features, has been recorded. The species is characterized by linear valves with almost parallel margins in the mid-valve, rostrate apices and striae that are partly biseriate, coarsely punctate and distantly spaced. In this study, it is described as a new species Aneumastus visovacensis sp. nov. Its morphology is documented with light and scanning electron microscopy, described in detail, and compared with the most similar species from A. tusculus species complex.

The progress of the taxonomy of cyanobacteria should be realized from the synthesis of all data, obtained by any method or procedure. Such synthesis must be as complete as possible. Phylogenetic reconstructions exhibit often conflicts with morphological characters. Taxa above the genus level are often polyphyletic, which introduces confusion into the cyanobacterial taxonomic classification. This article attempts to synthesize results from available literature and to propose a novel view of the taxonomy of cyanobacteria on the level of families and orders.

Jaromír Lukavský was born on 22 September 1943 in Neumětely. In the 1960s, he studied in Prague at the Department of Botany, Faculty of Science, Charles University under the guidance of the legend of world algology, professor Bohuslav Fott. Thanks to this, he gained a very solid background in the determination of algae, and this is also probably where his lifelong interest in floristic work stems from. Although the current advancements of molecular methods offer possibilities that were difficult to imagine previously, we increasingly find that a well-founded view on a sample under the light microscope is indispensable. Jaromír belongs to a small group of people who can provide it.

A filamentous, heterocytous cyanobacterial strain FACHB-3638 was isolated from Yongzhuang Reservoir, a tropical drinking water reservoir on Hainan Island, southern China. This cyanobacterium formed macroscopic, felt-like mats on submerged concrete substrates, covering extensive areas of the shallow riverbed. The filaments were isopolar, cylindrical, and nearly straight or flexuous, exhibiting infrequent scytonematoid false-branching and producing firm, often layered and colored sheaths. Morphologically, the strain resembles members of the Scytonemataceae family, particularly Brasilonema, but phenotypically differed from other scytonematoid genera in thallus form, branching pattern, trichome structure, heterocyte positioning, and habitat preference. Phylogenetic analyses based on 16S rRNA gene sequences placed this strain in a clade distinct from closely related genera within the family Scytonemataceae. The 16S rRNA sequence of this strain shared less than 95% genetic identity with currently described Scytonemataceae genera. Based on a polyphasic approach including data on morphology, ultrastructure, ecology, 16S rRNA phylogeny and secondary structure, we propose Parabrasilonema hainanensis gen. et sp. nov. as a new cyanobacterial taxon. Additionally, phylogenetic analyses showed that strain FACHB-3638, along with uncultured cyanobacteria clone Z32 from wall biomats in a deep sinkhole in northeastern Mexico, forms a well-supported monophyletic clade, exhibiting 97.51-99.28% nucleotide similarity. These findings suggest that these uncultured cyanobacteria likely belong to the genus Parabrasilonema, broadening our understanding of its diversity across distinct habitats.

The genus Staurosira comprises a limited number of small-celled araphid diatom species that are often quite common in waterbodies worldwide. Despite a global occurrence, their taxonomic identity is poor­ly known, due to the lack of good knowledge of their type materi­al. In the present contribution, the taxonomic history and morphology of four often-cited Staurosira taxa are unravelled based on light and scanning electron microscopy analysis of the original samples collec­ted by Christian G. Ehrenberg. Staurosira construens and S. pinnata, both described from New Haven (Connecticut, USA), showed suffi­cient differences to be kept as separate species. Staurosira binodis, first observed in a fossil diatomite sample from Santafiora (Italy), shows some morphological variability in its central constriction. Finally, Staurosira venter is typified using a fossil diatomite sample from Berlin (Germany), settling a decade-long uncertainty about its exact morphology. In addition to these four Ehrenberg taxa, two unknown Staurosira taxa, also present in the original material, are described as new: Staurosira venteriformis sp. nov. and S. venterilonga sp. nov.

Disconnected pools are temporary habitats of great ecological importance that can maintain high aquatic biodiversity. However, little is known about the composition and distribution of algal communities in the Mediterranean basin. During a diatom flora study conducted on the Iberian Peninsula, several populations of unknown taxa were found. Detailed observations with optical and scanning electron microscopes allowed for the description of three new taxa to science: Sellaphora temporalis sp. nov., Sellaphora catalonica sp. nov., and Nitzschia curvirecta sp. nov. Differential diagnostic criteria with respect to similar taxa are briefly described, and ecological information is provided. All of this highlights the importance of disconnected Mediterranean pools, often overlooked in terms of conservation.

Three Tryblionella species found at the same locality in Lake Qinghai, the largest inland saline water lake of China, are studied by using light and scanning electron microscope. One species is proposed as new to science and named Tryblionella qinghainensis sp. nov. The other two species are identified as T. apiculata W. Gregory and T. levidensis W. Smith. Tryblionella qinghainensis sp. nov. is characterized by its linear-lanceolate valve outline, broad axial sternum, a stria density to fibula density ratio of ca. 1.9:1, alveolate striae, and a simple standing lamella-like marginal ridge unperforated. Several ultrastructural details for T. apiculata and T. levidensis are revealed for the first time, especially the ultrastructure of their marginal ridges. The structure and shape of the marginal ridge in these three Tryblionella species are different, and the ultrastructure at the junction between the marginal ridge and the distal mantle can also vary for each individual species. The ultrastructure of the marginal ridge and distal mantle may be used as important diagnostic characters for the species of the genus Tryblionella.

During a survey of the terrestrial moss diatom flora in Greenland, two unknown Humidophila species were observed that could not be identified using the currently available literature. Detailed morphological analysis using both light and scanning electron microscopy revealed sufficient morphological differentiation from known species to describe these as new species: H. helderiana sp. nov and H. mitosis sp. nov. Formal descriptions are presented, each illustrated by light and scanning electron micrographs, and the new species are compared with similar Humidophila taxa worldwide. Additionally, eight previously described species which were also observed are discussed, and Humidophila mochalovae comb. nov., formerly belonging to the genus Diadesmis, was transferred to Humidophila. Of these known species, six have not been previously reported from Greenland, expanding their known geographic distributions. Our findings bring the total number of Humidophila species globally to 87 and contribute to a better understanding of the terrestrial Arctic diatom flora.

During the exploration of cyanobacterial diversity of the semi-arid region of northwest India, a non-heterocytous cyanobacterium was isolated from an aquatic habitat and characterized using a polyphasic approach based on morphology, ecology and sequencing of the 16S rRNA gene. Two strains (AT2016/6; SN2021/02) were isolated and characterized by cells longer than wide, the presence of a thick sheath, and the formation of nodules. 16S rRNA gene sequences revealed that the strains formed a highly supported, distinct clade within the Nodosilineales, ranging from 89.52% to 92.76% similarity to other strains. Secondary structures (the D1-D1´, BoxB, and V3 helices) of the 16S-23 rRNA Internal Transcribed Spacer (ITS) regions of both novel strains exhibited unique sequential differences from phylogenetically related taxa. Based on the combination of morphological characters and well-supported phylogenetic data, we describe a new genus and species: Pushkarnema curajae gen. et sp. nov. in accordance with the International Code of Nomenclature for Algae, Fungi, and Plants (ICN).

The genera Lobocharacium Kugrens, Clay et Aguiar, Characiosiphon Iyengar, and Characiochloris Pascher form a distinct phylogenetic clade within the order Chlamydomonadales, here referred to as the Characiosiphonia clade. These taxa share a similar overall cell morphology, characterized by a narrowed apex and a basal attachment structure. However, these genera also exhibit different characters, and previous studies have not provided a comparative morphological analysis to distinguish among the three genera within this clade. In this study, we conducted detailed morphological and molecular investigations of four algal strains. Phylogenetic analyses based on 18S rDNA and rbcL sequences confirmed the position of the three genera within the Characiosiphonia clade. The molecular analyses indicate that the genus Characiochloris is not monophyletic. Based on its unique features and the irregular contractile vacuoles in cells, we describe the strain - FACHB-3671 as a new species and named it Characiochloris papillata sp. nov. Given the current limitations in the molecular data of Characiochloris Pascher (particularly the lack of its type species), further research is necessary to resolve its polyphyly and clarify the taxonomic boundaries of the Characiosiphonia clade.

Fragilaria vaucheriae is one of the most common Fragilaria species in Europe, typically reported from impacted, eutrophic water bodies. Despite its ubiquity, the species presents a broad morphological variability, urging a complete taxonomic revision based on the analysis of the morphology of a substantial number of historic and recent populations. In the present study, type material of Exilaria vaucheriae, Fragilaria rinoi, and Echinella fasciculata β [var.] truncata was investigated using LM and SEM observations, together with more than 10 historic and recent populations. The results based on these comparisons show that Fragilaria vaucheriae is most likely a rather rare Fragilaria species in Europe and that most populations should be identified as Fragilaria truncata, a new combination made here based on Echinella fasciculata β truncata. The observations made in this study also resulted in the description of several new species, often with distinct ecologies and distributions: Fragilaria catenarinoi Van de Vijver et D.M.Williams sp. nov., F. kellyana Van de Vijver, D.M.Williams et Ector sp. nov., F. landnama Van de Vijver et Iris Hansen sp. nov., F. thingvellirensis Van de Vijver et G.S.Jónsson sp. nov., F. vandekerckhoveana Van de Vijver sp. nov., F. vaucheriaefalsa Van de Vijver et D.M.Williams sp. nov. and F. vaucheriaerobusta Van de Vijver, C.E.Wetzel et Ector sp. nov. Important features to discriminate the different species include valve outline (linear versus lanceolate), the presence of 'shoulders' beyond the apices, the presence of striae (and the formation of colonies), the stria density and the shape and structure of the central area. Using an analysis of the associated diatom flora, the ecological preferences of each taxon are briefly discussed.

Numerous organisms play a host role for a variety of marine and freshwater diatoms and many have yet to be studied in detail. In particular, along the Argentine coast, there have been very few studies on epizoic diatoms. Through the analysis of ascidians, decapods, echinoderms and gastropods sampled from Atlantic Patagonian waters (San Jorge Gulf), this is the first study in the region on epizoic diatoms found on benthic macroinvertebrates. Thirty-one potential host samples, including 14 macroinvertebrates taxa, were examined from different stations. The epizoic diatom taxa found at the highest relative abundance, namely Cocconeis patagonica sp. nov., Pseudogomphonema kamtschaticum and Tabularia investiens, were analyzed using light and electron microscopy, and hence they are described in detail and compared with other species. Cocconeis patagonica sp. nov. belongs to the C. scutellum complex, but its particular raphe-valve (RV) valvocopula ultrastructure and striation defines it as new. Diagnostic characters are discussed for T. investiens. Pseudogomphonema kamtschaticum is reported for the first time in the Atlantic Patagonian waters.

Coelastrella Chodat is a green alga frequently found in subaerial habitats that is typically characterized by ribbed cell walls. During our research on the soil algal community of sodic-saline slicks in Warren Prairie Natural Area, Arkansas, USA, we found several al­gal strains with the features of Coelastrella. We also expanded our study to include soil samples from sites in the barrens grassland soil around the sodic-saline slicks, which also yielded Coelastrella strains. There were also other strains that lacked ribbed cell walls but could be placed in the genus Coelastrella using nuclear ribosomal 18S and ITS1-5.8S-ITS2 DNA sequences. Analysis of ribosomal ITS se­quences, plastid tufA sequences, and morphology revealed four distinct taxa among these strains, including two new species, C. salsodica and C. subsphaerica, and two new va­rie­ties of C. yingshanensis, C. yingshanensis var. apiculata and C. yingshanensis var. ovata. C. salsodica, C. subsphaerica, and C. yingshanensis var. apiculata were only found in the sodic-saline slicks, whereas C. yingshanensis var. ovata was only found in the barrens grassland soil. To date, no other Coelastrella species have been found in these sites.

The Prasiola-like Prasiolaceae includes some 35 species of monostromatic green algae found in a wide range of habitats, including marine, freshwater, and terrestrial environments, across polar, cold, temperate, and subtropical regions. They exhibit considerable phenotypic plasticity, complicating identification based on morphology alone. Here, we used a approach based on full-length 18S rDNA amplicon sequencing to identify Prasiola-like specimens from China. Amplicon sequence variants (ASV) belonging to Prasiolaceae were detected in material collected at W'umonshan, Yunnan Province, China, and living specimens were subsequently collected from the corresponding sampling locations. We here designate a sequenced specimen as epitype as the holotype of Prasiola yunnanica C.-C. Jao is a formaldehyde-fixed specimen that cannot be sequenced. By combining molecular phylogenetics and morphological observations, we provide a comprehensive assessment of three Prasiola-like collections, identified through integrative taxonomy, as Eaprasiola yunnanica (C.-C.-Jao) comb. nov., a species distinct from Eaprasiola japonica (Yatabe) Heesch, Guiry et Rindi from Japan. This finding highlights the effectiveness of the reverse taxonomy approach in detecting rare algae, and emphasizes the importance of integrative methods for achieving a thorough and accurate assessment of algal taxonomy and diversity.

In the framework of a study of the genus Luticola Mann we collected and processed samples from different ecoregions of Argentina, analyzed them with light microscopy (LM) and scanning electron microscopy (SEM). In aerophilous samples collected in Misiones Province, Argentina, we found colonial specimens. The aim of this work is to elucidate the identity of the colonial forms found in aerophilous samples in NE Argentina. In the present study, we describe the genus Neoluticola Simonato, Sala et Kociolek and four species: Neoluticola spinosa Simonato, Sala et Kociolek sp. nov., Neoluticola arrechensis Simonato, Sala et Kociolek sp. nov., Neoluticola alegrensis Simonato, Sala et Kociolek sp. nov., and Neoluticola salvadoriana Simonato, Sala et Kociolek. Neoluticola comprises a group of aerophilous colonial species that share with Luticola a conspicuous isolated pore in the central area, distinctly punctate striae, and marginal channels. The new genus differs from Luticola in the location of the isolated pore on the valve face/mantle junction, colonial life habit, special structures (spines or silica projections) that join cells together, very thin slit-like areolae on the valve mantle, an elevated fascia expanded side to side, internal proximal raphe ends strongly curved, and fimbriate girdle bands. We compare the species of the new genus with morphologically similar ones from Luticola and discuss the geographic distribution of Neoluticola gen. nov.

During the investigation of freshwater biodiversity of Xizang Autonomous Region, diatom samples were collected from several habitats and two new species were discovered and are formally described herein, namely, Gomphosinica stoermeri Liu, Kociolek et Li sp. nov., and Gomphosinica qii Liu, Kociolek et Li sp. nov. Both of these new species have biseriate striae, straight raphe ends, pseudosepta at both ends and a hooded stigma covering in the central area. Gomphosinica stoermeri can be separated from other similar species by its clavate outline, bluntly rounded headpole, rounded footpole, small and rounded central area formed by 2-4 short striae. Gomphosinica qii is relatively small, has small and more elliptical valves, small bluntly headpole and narrow footpole, round to rhombic central area formed by 2-6 short striae. Specimens which appear very similar to Gomphosinica hedinii were observed, but the outline and shape of central area do not match the original of Gomphosinica hedinii; herein we document these specimens and designate them as "Gomphosinica cf. hedinii". Gomphosinica linearis was also observed, and we provide a more detailed description of it based on LM and SEM. Differences between the two newly described species and other known species of the genus are also discussed.

Fragilaria gracilis is one of the most reported Fragilaria species in Europe, observed in a broad range of water bodies, ranging from (ultra)oligotrophic rivers to even eutrophic lakes. A revision of this important taxon based on the analysis of the morphology of a large number of historic and recent populations was highly needed. In the present study, type material of Fragilaria gracilis and several related taxa such as Synedra radians, Fragilaria pseudolaevissima, S. utermoehlii, F. aquaplus, F. boreomongolica and F. tridentina together with more than 10 modern populations were investigated using LM and SEM observations. The results based on these comparisons show that Fragilaria (Synedra) radians is the name for the taxon formerly known as F. gracilis. Moreover, detailed analysis demonstrated that F. pseudolaevissima and Synedra utermoehlii are conspecific with F. radians and should be considered as heterotypic synonyms. The observations made in this study also resulted in the description of several new species, often with distinct ecologies and distribution areas: Fragilaria huerlimannii Van de Vijver sp. nov., F. acerosa Van de Vijver, C.E.Wetzel, Jarlman et Ector sp. nov., F. neglecta Van de Vijver, C.E.Wetzel, Jarlman et Ector sp. nov., F. heudreana Van de Vijver, C.E.Wetzel et Ector sp. nov., F. eutraphenta Van de Vijver, Kusber et D.M.Williams sp. nov., and F. mertensiana Van de Vijver, C.E.Wetzel et Ector sp. nov. Using an analysis of the associated diatom flora, the ecological preferences of each taxon are briefly discussed.

The taxonomic concept of Actinella guianensis Grunow is well-established in the literature. However, during the analysis of recent samples from two Amazon blackwater habitats, we found an uncommon and oddly shaped Actinella taxon, which corresponds to what is reported in Grunow's drawings in Van Heurck's Atlas as the type species of A. guianensis. To understand the identity of the uncommonly shaped Actinella, we revisited the type materials and the literature citing A. guianensis and compared them with the population found in samples recently collected. Two distinct morphologies were found in the original material. These morphologies differed mainly in the shape of the headpoles, with one being cordiform (heart-shaped) and the other bulbous. Furthermore, differences were observed in the shape of the footpoles, with one being characterized by enlarged and cuneated to protracted apices, while the other presents a spoon-like shape. Following the analysis of the original material, modern samples, and the literature, we propose Actinella cordiformis Coêlho, Silva-Lehmkuhl, Kociolek, Lehmkuhl et Ludwig sp. nov. for the species having a cordiform headpole.

A new genus and species of freshwater diatoms from the Guangxi Autonomous region of southern China were studied with light and scanning electron microscopy. The newly proposed genus has several features that assign it to the Naviculaceae, including symmetry about the apical, transapical and pervalvar axis, slit-like areolae that are occluded internally by fine hymenes, hook-like external distal raphe ends and the presence of an internal auxillary rib bordering the raphe sternum. These features also suggest a strong morphological similarity with the genus Navicula. The new genus and species, however, have several external flaps of silica on the valve face and apex that give the raphe a bifurcate appearance, a feature not found in any Navicula species and more reminiscent of the genus Neidium. Also present is a hooded structure on the auxillary rib that covers the central nodule and expanded central area on both sides of the raphe, on one side resembling a forked expanded fascia. These features of the exterior and interior of the valve are not seen in other Navicula species, or in other genera within the family. The proposed new genus and species, Trialacinia guangxiana joins other diatom genera and species being endemic from the Guangxi Autonomous region of China.

The naming of organisms long known as "blue-green algae" or "cyanophytes", and more recently as "cyanobacteria", is currently governed by both the rules of the International Code of Nomenclature for algae, fungi, and plants (ICN) and the International Code of Nomenclature of Prokaryotes (ICNP) and a reciprocal principle of code coordination has been agreed so that names validated in either code are treated as valid in the other code. Under the ICN, both descriptive and typified names above the level of family are permitted, and the principle of priority does not apply but there is a recommendation that priority be applied to typified names. The current names in use, along with the typified or descriptive phylum/division names, and class names applied to cyanophytes, are discussed, and recommendations for their use are provided. We recommend adoption of the typified phylum name Cyanobacteriophyta Oren, Mareš et Rippka, 2022 in papers employing the ICN and Chroococcophyceae Hollerbach, Kosinskaya et Poljansky, 1953 as a class name that includes all cyanobacteria as currently conceived but with the caveat that further class names may come into use in the future.

The genus Simonsenia is characterized by the raphe system that opens into a longitudinal channel over a marginal keel, and small circular areolae, occluded by hymens. So far, the occurrence of Simonsenia species in Brazil is known only by two records of S. delognei, documented in light microscopy. Here, are described three new species of Simonsenia, one from karst freshwater environments and two from an estuarine stream. Also, we report S. delicatula for the first time to Brazil, in a lotic freshwater body. The new species are distinguished from each other and from similar Simonsenia taxa mainly due to size, valve contour, apices shape, morphology of transapical ribs, and number of areolae rows of the striae. This study is an important contribution to the taxonomy, diversity and distribution of the genus, still underestimated, especially in estuaries and karst of tropical regions.

Loricate golden algae (Chrysophyceae) are photosynthetic microorganisms characterized by a lorica, a rigid or semi-rigid protective casing made of organic material, sometimes reinforced with silica or iron. The lorica's diverse shapes and intricate ornamentation serve as both adaptive strategies and taxonomic markers. Here, we identified, for the first time, the molecular phylogenetic position of a loricate genus Chrysococcus, based on genetic investigations of two freshwater populations in Poland. The genus was resolved to form a well-supported clade with Chrysosaccus within the order Chrysosaccales. Accordingly, this order represents one of the morphologically most diverse lineages of Chrysophyceae, including naked flagellates, coccoid organisms, amoebae and flagellates dwelling in loricae, and mucilage-secreting cells. The phylogenetic resolution of Chrysococcus provides key evidence for understanding the evolutionary transitions within Chrysophyceae, highlighting the complex relationships between loricate and non-loricate taxa.

Ectorea stella Marquardt et C.E.Wetzel, gen. et sp. nov., a cruciform 'araphid' diatom is proposed from Quaternary deposits of the Colônia basin, Southeast Brazil, based on light and scanning electron microscopy observations. Type material of the morphologically most similar species Fragilaria inflatissima Hustedt was also examined and a new combination for the taxon is proposed as well. The new genus diagnostic features include valves strongly inflated transapically, presence of a wide hyaline sternum bordered by spines, inconspicuous striae composed of rounded areolae without volae or rotae and restricted to mantle or to the marginal valve face area, girdle composed of at least one open, narrow, non-perforated band, and the non-fimbriated valvocopula. We further call attention to the lack of structures that are usually observed in araphid diatom representatives, such as the apical pore fields, rimoportula, and mantle silica plaques along the valve mantle edge. Differentiation between species includes valve dimensions and morphology. Furthermore, Ectorea stella sp. nov. has valve face composed of a flat sternum with short marginal striae, opposite to the rough non striated sternum of Ectorea inflatissima, comb. nov. Regarding ecology, the new genus occurs in acidic oligotrophic environments. While E. inflatissima occurred in large oligotrophic rivers from the Amazon basin, the new species E. stella occurrence suggests a peat bog formation round the lake, and may indicate an increased lake productivity, probably in response to the peatland development in the catchment area.

During studies on the diversity of Frustulia in the state of Paraná, Brazil, two different morphological populations did not correspond exactly to any known described species. This paper describes these species as Frustulia lineata sp. nov. and Frustulia magnifica sp. nov. The samples were collected in lotic environments inserted in the south Brazil Atlantic Forest region. Frustulia lineata sp. nov. is mainly characterized by linear-lanceolate valves with small dimensions, sharing morphological similarities with Frustulia marginata Amossé and Frustulia saxonica f. indica Sarode et Kamat. Frustulia magnifica sp. nov. is significantly larger than other species of the genus, having morphological similarities with Frustulia aotearoa Lange-Bertalot et Beier, Frustulia bahlsii Edlund et Brant, Frustulia rhomboides f. occidentalis Sovereign, and Frustulia sanctarosae Lange-Bertalot et Sterrenburg. Studies using light and scanning electron microscopes have revealed that the morphology and dimensions of the central nodule and the porte-crayon were primary distinguishing features that substantiate the proposal of the new species.

In a comparative study on epiphytic diatoms in the Rivers Euphrates and Tigris (Iraq), one of the major drainage basins in the Middle East, we report a new species, Prestauroneis furatensis sp. nov., It was present in low abundances (up to 5%) solely in the summer samples of the River Euphrates on the macrophytes Ceratophyllum demersum, Typha domingensis, Potamogeton perfoliatus, and Najas minor. Light and scanning electron microscopic observations revealed distinct morphological traits that differentiated P. furatensis from other species, leading to its identification as a new species. Detailed physical-chemical parameters were taken and showed its occurrence - among others - under elevated conductivity conditions. The dominant diatoms co-occurring with this new species included Nitzschia gracilis and Mastogloia smithii on C. demersum, Gomphonema hebridense on T. domingensis, Nitzschia palea and Cocconeis placentula on P. perfoliatus. Nitzschia gracilis and Nitzschia palea on N. minor. In addition, Prestauroneis cruciculoides comb. nov. is validated.

The former Synedra rumpens complex has long puzzled diatom taxonomists. In the nineteenth century, many infraspecific taxa were described as varieties or forms of S. rumpens. In the present study, type material of Synedra rumpens and several infraspecific taxa such as S. rumpens var. fragilarioides and S. familiaris f. parva and f. major was investigated using LM and SEM observations. For comparison, the original material of several other relevant diatom taxa (such as Fragilaria perdelicatissima, F. spinaspeciosa, Synedra campyla, S. vaucheriae var. distans) was also analysed. The results based on these comparisons show that all infraspecific taxa should be split from Fragilaria rumpens. Fragilaria campyla is a new combination within the genus Fragilaria with F. parva and S. (rumpens var.?) familiaris f. major as synonyms. Fragilaria scotica is likewise a new combination in Fragilaria. Fragilaria metcalfeana is proposed as new name for Synedra familiaris var. neogena. The analysis of F. distans and F. fragilarioides confirmed their conspecificity, with F. fragilarioides having priority as name. Finally, two new species, F. pseudofamiliaris Van de Vijver, T.M.Schuster, Kusber et D.M.Williams sp. nov. and F. bahlsiana Van de Vijver, C.E.Wetzel et Ector sp. nov. are described. Using an analysis of the associated diatom flora, the ecological preferences of each taxon are briefly discussed.

Delicatophycus costei (Lange-Bertalot et Moser) Wynne, Cymbella bourrellyi Maillard, Cymbella latarea Maillard and Cymbella pernodensis Maillard are endemic to New Caledonia and show uncommon morphological features compared to the "sensu stricto" definition of their respective genus. Delicatophycus costei was described based on light microscopy and scanning electron microscopy (SEM) observations, confirming the generic LM diagnosis. However, the external view in SEM is atypical as both valve face and mantle are covered by longitudinal ribs, overlaying part of the zig-zag striae, generally accepted as the determinant generic feature. The three species of Cymbella have both apical pore fields and "stigmata". However, they show some specific morphological features compared to the more classically shaped Cymbella species. Cymbella bourrellyi has a narrow hyaline area on the valve face and the areolae are bordered internally by small outgrowths. Cymbella pernodensis is distinguished by internal biseriate striae. The internal morphology of Cymbella latarea is characteristic in having typical biseriate striae and bisected apical pore fields. In these three species, internally, the stigmata are continuous with the striae and appear as simple and only weakly separated structures at the end of the striae. The three species are also characterized by differences in the number of areola rows per stria externally and internally.