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We provide an update to our knowledge of the centric diatoms in the Tonle Sap Lake (Cambodia) by providing a new and highly detailed iconography of all observed taxa based on light and scanning electron microscopy. We highlight a distinctive flora, including a new genus Praecyclostephanos gen. nov. and five taxa new to science: Aulacoseira micropunctata sp. nov., A. spiralorimoportula sp. nov., Praecyclostephanos boengchhmariensis sp. nov., Stephanodiscus tonlesapensis sp. nov. and Urosolenia anlongreangensis sp. nov. The flora is mainly dominated by several species of the genus Aulacoseira. Within the Aulacoseira populations forming the background of the diatom community, taxa that reveal the change in environmental conditions appear sporadically, often as blooms. The wide range of life-forms related to their ability to float is another remarkable aspect of the centric diatom flora. This variability appears at several taxonomic scales. At the genus level, colonial and solitary life-forms are very well represented in their diversity. At the sub-genus level, mainly among the Aulacoseira species, communities present a wide range of buoyancy metrics. Accordingly, in addition to the taxonomic review, we provide additional information related to their potential as bioindicators to monitor the hydrodynamic aspects of the lake in both space and time.

The genus Semiorbis was erected by R.M.Patrick in 1966 as monotypic based on the relatively rare taxon Semiorbis hemicyclus. Defining characters for Semiorbis include strongly arcuate valves, short eunotioid raphe branches, well-developed external costae with spine-like projections on the virgae, lack of rimoportulae, and a broader dorsal mantle. New populations of Semiorbis were found in the central USA (Wisconsin) on Outer Island, Apostle Islands National Lakeshore, along southeast Lake Superior, from a lake in New Jersey (USA), and from a small arctic lake in Nunavut, Canada. The population in Outer Lagoon, a shallow embayment cut off from Lake Superior by a long-shore bar, provided documentation of living cells and colonies of Semiorbis. We examined the morphology, ecology, and taxonomy of these new populations using light and scanning electron microscopy, traditional morphometrics, and sliding landmarks shape analysis. We compared these populations to European populations of Semiorbis hemicyclus and North American populations of Semiorbis rotundus and Semiorbis catillifera. We determined that the population found in Wisconsin represents a new species herein described as Semiorbis eliasiae Edlund, D.R.L.Burge, N.A.Andresen & VanderMeulen sp. nov., the New Jersey (USA) population is Semiorbis rotundus, and the Nunavut (Canada) population represents a North American population of the generitype Semiorbis hemicyclus.

During a survey of the sub-Antarctic diatom flora, several populations previously identified as Fragilaria alpestris were reanalysed and compared with type material of the latter species. The morphological ultrastructure of the type of F. alpestris, the sub-Antarctic populations and an additional population of F. cf. alpestris from Spitsbergen has been analysed using light and scanning electron microscopy observations. The analysis revealed that Fragilaria alpestris clearly belongs to the genus Fragilaria whereas the sub-Antarctic populations show all morphological features of the genus Staurosira. Comparison with similar taxa worldwide showed that these populations belonged to an unknown taxon that could not be identified using the currently available literature. A new species, Staurosira vandenbusscheana Van de Vijver sp. nov. is therefore described. The F. cf. alpestris population from Spitsbergen forms long, ribbon-like colonies, unlike the type of F. alpestris that never produces band-like colonies. Following the observation of additional morphological differences such as the presence of two rimoportulae and the shape of the linking spines, the Spitsbergen taxon is described as a new species: Fragilaria confusa sp. nov. The three taxa described herein share a number of morphological features. Their specific features are detailed below along with notes on their ecology. A literature survey and an analysis of the records for F. alpestris are given.

During a revision of the genus Fragilaria in Europe, two unknown Fragilaria taxa were observed in Erken Lake, Sweden, that showed some resemblance to Fragilaria perminuta, a species described in the nineteenth century from the Great Lakes in the United States. The type material of Synedra perminuta from Lake Erie, U.S.A. (Grunow sample 2592) was analysed. Detailed morphological analysis, using both light and scanning electron microscope observations and comparison with the type material, showed that both taxa from Sweden should be described as new species: Fragilaria goeyersiana sp. nov. and F. vandevondeliana sp. nov. The separation of the two taxa is based on valve outline, shape of the apices and stria density. Comparisons are made with similar taxa and brief notes on their ecology are added.

During a survey of the terrestrial diatom flora of the Maritime Antarctic Region, an unknown Luticola taxon that could not be identified using the currently available literature was observed on two islands of the South Shetland Archipelago. After a detailed morphological analysis and comparison, the unknown taxon is described as Luticola puchalskiana sp. nov. The new species can be separated from other Luticola species based on its valve dimensions, stria density and the shape of both central and terminal raphe endings. Two populations of the new taxon were observed in samples collected from terrestrial habitats. The morphology of Luticola puchalskiana is elaborately described and illustrated using both light and scanning electron microscopy observations. A comparison is made with a large number of other morphologically similar Luticola species from the entire (sub)Antarctic Region.

Hyalosira gene sequences are divided into two clades within different families. We examined authentic material of Hyalosira (isotype material of H. obtusangula, synonymous with H. delicatula) and voucher specimens of published sequences, and pooled our observations of Hyalosira-like taxa from benthic and epizoic habitats in several parts of the globe. The two molecular clades corresponded to two morphological groups, with Hyalosira obtusangula associated with Grammatophoraceae. We emend the description and provide lectotypification for Hyalosira and propose Placosira to encompass the taxa in the other clade, associated with Rhabdonemataceae. We propose that Hyalosira has uniseriate to triseriate striae, sometimes different on valve face and mantle. Copulae in most species had shallow septa, though in one they were moderately deep. All species had girdle bands bearing two rows of areolae separated by a midrib. We name five new species of Hyalosira. Morphologies of taxa in the Placosira clade were superficially similar to Hyalosira but differed in having areolae with ricae, a single row of areolae on the girdle bands, and tubular rimoportulae on the valve-face-mantle junction. Hyalosira hustedtiana Patrick should revert to its original position in Striatella until the appropriate genus can be determined. We emend Rhabdonematales to encompass Rhabdonemataceae, Grammatophoraceae and Tabellariaceae. (C) 2021 Elsevier GmbH. All rights reserved.

During a survey of the diatom flora of the Adegoy River (Krasnodar Territory, Russia), an unknown Fragilaria species (Bacillariophyta) was found that could not be identified using the currently available literature and here we describe it as a new species. The morphology of Fragilaria irregularis sp. nov. was studied using light and scanning electron microscopy and compared to similar species including Fragilaria deformis, F. rinoi, F. septentrionalis and Fragilariforma bicapitata. It differed from these taxa in several characters. Most observed valves showed an irregular striation pattern, a feature not observed in other species. Other important differences include valve outline (linear with parallel margins) and stria density (7–14 in 10 µm, lower compared to all other species). The new taxon has a linear valve outline with parallel to weakly convex margins, subcapitate apices and a very irregular, coarse striation pattern.

Like aquatic diatoms, terrestrial diatoms are sensitive to multiple environmental factors such as pH, anthropic disturbances, soil moisture and nitrogen. While most aquatic diatom species have well-known autecological values for several important variables, qualifying them as biological indicators, this potential has not yet been untapped for terrestrial diatoms. Here, we aim to establish autecological values for pH and soil moisture content using weighted averaging for common, widespread terrestrial diatoms and compare them with previous calculated indicator values and tolerance ranges. In order to provide robust autecological values, we combined the data of ecological studies carried out across a range of climate conditions. We found that our validation metrics improved considerably after removing samples collected in anthropic disturbed habitats, suggesting that anthropic disturbance is the principal factor defining taxon occurrences. Besides our results showing similarities with previous studies, they also showed a significant improvement on the existing indicator values. Moreover, we expanded the list of terrestrial diatoms to 249 taxa that may serve as environmental markers in different research fields.

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 genus Opephora currently contains 37 species and 27 infraspecific taxa. However, the existing literature reveals a wide morphological diversity and the need to establish defining characters to circumscribe the genus as a cohesive and, perhaps, monophyletic group. The type material of Opephora pacifica, the generitype, is analysed. We emend the description of both the species and the genus, the latter also based on published light and scanning electron microscopy observations of closely related species. After review of the available literature, we determined that currently only two species can be ascribed with certainty to the genus Opephora: O. pacifica and O. marina. Based on available literature, it is highly likely that O. fragilarioides also belongs to this genus. We present a table with all known species and infraspecific taxa and make comments regarding their recent transfer to other genera, their current accepted nomenclature, and the genus to which they should probably be ascribed pending the collection of further information.

During a biomonitoring assignment in the Swiss canton Ticino, an unknown Fragilaria taxon was discovered that could not be identified using the currently available literature. The results of a morphological comparison with the type material of F. recapitellata, based on light and scanning electron microscopy, showed that the new Swiss taxon has sufficient differences to be separated as a new species: Fragilaria subrecapitellata sp. nov. The new species can be separated by its lanceolate to elliptic-lanceolate valve outline with convex valve margins, and its smaller valves compared to F. recapitellata. The distribution and iconography of F. recapitellata in literature data is analysed. As a result of this analysis, Fragilaria deformis is appointed as the correct name for the taxon generally known as F. candidagilae or F. capucina var. capitellata (Grunow) Lange-Bertalot in Krammer & Lange-Bertalot.

International audience; An unknown Pinnularia taxon was recorded during a survey of the limno-terrestrial diatom flora of some hot springs in the Val Travers area (Grande Terre, Iles Kerguelen, sub-Antarctic region). The morphology of the species was investigated using both light and scanning electron microscopy. Based on these results, the species could not be identified using the currently available literature and is therefore described as a new species Pinnularia schoelynckiana sp. nov. The new species is characterized by rhombic-lanceolate valves, radiate, geniculate striae changing into strongly convergent near the apices and an undulating, lateral raphe. A detailed morphological comparison is made with similar Pinnularia species, described from the Antarctic Region and worldwide. Brief notes on the associated diatom flora and its ecology are added.

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. scalarifonn 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 mu m) and more slender (1.0-1.5 mu m) 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 phytogeny, Anaulus vallus Nikolaev, previously included within the genus Denticila, is transferred to the genus Nagumoea. This brings the current number of the genus members to five. Ecological preferences of Nagumoea are briefly discussed.

Psammothidium manguinii is a common constituent of the limnoterrestrial diatom flora of the Antarctic Region. The species shows a broad variability in several morphological and morphometrical features such as valve outline, valve width, striation pattern and length/width ratio. Analysis of the type material of Achnanthes manguinii, described by HUSTEDT in 1952, and A. manguinii var. elliptica, described by Manguin two years later, together with an analysis of a large number of P. manguinii populations from the sub-Antarctic Region (with samples from all major islands in the southern Atlantic, Indian and Pacific Ocean), resulted in a clear morphological revision of the species. Four new species are described, P. acutomanguinii sp. nov., P. antarcticum sp. nov., P. mannensianum sp. nov. and P. hodgsonii Van de Vijver et Verleyen sp. nov., whereas the former variety elliptica is brought to species level: P. ellipticomanguinii nom. et stat. nov. The morphology, ecology and distribution of all species are discussed and a morphological comparison is made.

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 (Ostrup) Lange-Bertalot and Planothidium frequentissimum (Lange-Bertalot) Lange-Bertalot. Eight species from freshwater enviromnents 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.

During a survey of the epizoic diatom flora on carapaces of loggerhead sea turtles (Caretta caretta) from the Adriatic Sea, a relatively small population of an unknown amphoroid species was observed, presenting some morphological similarities with the genera Lunella and Catenula. Due to the small size and the lack of distinct structures visible in LM, the observations of its ultrastructure under very high magnification in the scanning electron microscopy (SEM) proved to be critical in taxon delineation and indicated that it should be separated as a new Catenula species. The new species is characterized by very small, dorsiventral valves, striae composed of 1–3 small, marginally placed areolae, a very simple raphe structure lacking terminal raphe fissures, straight simple central raphe endings, the absence of helictoglossa and a distinct central nodule, the latter often discernible in LM. Typical ghost striae, reported to be one of the main morphological features of the genus Catenula, are very faintly present and only visible in the valve interior. The new species is illustrated using both LM and SEM observations and compared with all other known Catenula and Lunella species.

Background and aims – During the past two decades, the subantarctic diatom flora has been the subject of several detailed taxonomic revisions, resulting in the description of a large number of new species. During a survey of the freshwater diatom flora of Macquarie Island (southern Pacific Ocean), an unknown Navicula species was observed showing resemblance to Navicula gottlandica. Populations of similar diatoms (previously reported as N. gottlandica) from Tasmania were also investigated. We here present a detailed morphological analysis of these diatoms, and compare it with the type material of N. gottlandica. Methods –Materials were analysed using Light and Scanning Electron Microscopy. Key results –The southern hemisphere populations represent two hitherto unknown taxa here described as Navicula bergstromiana and N. eileencoxiana. Important morphological differences include valve shape, stria density, shape of the central area, ultrastructure of the external central raphe endings, presence of a distinct internal accessory rib, and the relative width of the external longitudinal silica strips covering the valve face with respect to the longitudinal fissures separating these strips. While the new taxa show some affinity with the genus Haslea, the internal apical structure of the raphe, the external structure of the terminal raphe fissures and the central raphe endings (often with tooth-like protrusions, creating the impression of a satellite pore), and the apparent lack of the typical sandwich-type Haslea valve ultrastructure support the position of N. gottlandica and both new taxa within the genus Navicula. Conclusions – The description of two additional species with close similarities to N. gottlandica (i.e. possessing the typical longitudinal striae/silica strips and tooth-like protrusions in hooked central raphe endings) suggests that the N. gottlandica species group is more diverse than previously thought. The existence of closely similar Navicula species recently described from rivers in tropical South America but also from marine littoral samples in South and North America and China, raises intriguing questions about their phylogenetic relationships, ecology and biogeography.

The diatom genus Proschkinia is a common element of biofilms covering diverse substrata in saline inland or shallow coastal environments. It can be distinguished from other naviculoid taxa by its lanceolate valves with a fistula located within the central area and numerous open girdle bands with a U-shaped cross-section and a single row of perforations on the internal side of the fold. Despite this distinct morphology, frustules of Proschkinia are typically weakly silicified and often overlooked when cleaned diatom material is analysed. The current paper describes six new species of Proschkinia: P. browderiana sp. nov., P. lacrimula sp. nov., P. maluszekiana sp. nov., P. sulcata sp. nov., P. torquata sp. nov. and P. vergostriata sp. nov., found in numerous samples of marine organisms, such as sea turtles (including sea turtle museum specimens), sea turtle-associated barnacles and seagrass from across the three oceans. Some of the newly described taxa were found on multiple individuals belonging to different sea turtle species, whereas others were in samples collected from different continents. Molecular phylogenetic analysis indicated that examined Proschkinia strains formed a monophyletic clade, sister to Fistulifera.

The present investigation is based on detailed taxonomical analyses combining light microscopy (LM), scanning electron microscopy (SEM) and critical reviews of publications and type material. This method revealed a higher number of diatom taxa than that reported for the Altiplano, reports that are based on LM and SEM, but force-fitting the taxa into their European relatives. It also became evident that some taxa often reported from the Altiplano do not occur or are less common in this region and that misidentifications are the consequence not only of force-fitting, but also of misinterpretation of the original protologues and illustrations (taxonomic concept drift). These findings have important repercussions on past palaeoecological assessments for the Altiplano, which have been based on ecological information for taxa developing in ecosystems of highly contrasting conditions. Here we present the case of three araphid diatoms, which were reported as known taxa from Europe and elsewhere, but in fact correspond to taxa described as new for the Altiplano or unpublished taxa. It is recommended that: (1) a flora for this region is developed utilizing sound microscopical data and reviewing pertinent type material, (2) key common taxa used for past palaeoecological studies in the Altiplano are reviewed using a taxonomically thorough and critical method, and (3) future palaeoecological studies for the Andes are supported by prior detailed taxonomical analysis.

Rhoicosphenia is a relatively small genus with about 30 species and 30 infraspecific varieties. Over the past decade there has been a renewed interest in describing previously undocumented diversity in Europe, Asia and North America, from fossil and extant material, and from marine and freshwater environments. Of the ca. 60 Rhoicosphenia taxa, one species, R. lesothensis, has already been transferred out of the genus. During a literature review of the genus, a passage by Hustedt suggesting the need to transfer another species, R. vanheurckii, out of the genus was examined. Our morphological investigations result in the transfer of R. vanheurckii to the genus Planothidium. Although this diatom does not bear the cavum or sinus typical of most Planothidium species, it fits with the other characters of the genus and will retain the specific epithet, as P. vanheurckii (Grunow) E.W. Thomas, Van de Vijver & Kociolek comb. nov.

We analysed syntype material of Odontidium harrisonii W. Smith, Odontidium mutabile W. Smith, Odontidium tabellaria W. Smith, Odontidium tabellaria var. beta W. Smith, Odontidium parasiticum W. Smith, Odontidium parasiticum var. beta W. Smith and Fragilaria brevistriata Grunow in Van Heurck. A combination of light and scanning electron microscopy revealed that taxonomic drift led to currently misconstrued concepts of many of these taxa. Preservation of type materials allowed morphological study of each taxon in detail. The following new combinations, new names and new statuses are presented: Staurosirella harrisonii (W. Smith) E. Morales & C.E. Wetzel comb. nov., Staurosirella mutabilis (W. Smith) E. Morales & Van de Vijver comb. nov. and Pseudostaurosira smithii E. Morales & Ector nom. nov. stat. nov. Nomenclatural and ecological discussions, based on historical and current literature, are presented for each taxon. The study of type materials is a necessary task in order to improve current databases used for taxonomic and ecological purposes, and such a study should be an essential component of large-scale palaeo or neo-limnological research programs.

During a survey of the diatom flora of some caves on Ile de la Possession, the main island of the Crozet archipelago, a small, unusual naviculoid taxon was observed, initially identified as Fallacia lenzii. The new taxon is described as Fallacia emmae but it shows features of two related genera: Fallacia and Germainiella. Thorough morphological research revealed details that, on the one hand, contradicted its placement in Fallacia, such as the relatively low number of poroids on the conopeum, the absence of external canal apertures beside the raphe slit (Fallacia-feature), and striae that are composed of one slit-like areola (Germainiella-feature). The morphology and taxonomy of the new taxon are discussed and questions are raised about the validity of genera recently split off from the genus Navicula on the basis of one, or occasionally two, morphological features.

Five unknown taxa belonging to the newly established genus Humidophila were found during ongoing taxonomic revision of the freshwater and limno-terrestrial diatom flora of the Maritime Antarctic Region. These taxa were previously identified as Diadesmisarcuata, D.biscutella, D.comperei and D.ingeae, but detailed light and scanning electron microscopy observations allowed their clear separation from the already known taxa, and resulted in the description of five new species: Humidophilasceppacuerciae Kopalova sp.nov., H.australoshetlandica Kopalova, Zidarova & Van de Vijver sp.nov., H.keiliorum Kopalova sp.nov., H.deceptionensis Kopalova, Zidarova & Van de Vijver sp.nov. and H.vojtajarosikii Kopalova sp.nov. All five new taxa are compared with the morphologically most similar taxa, and their ecology and biogeography are discussed. Although the genus Humidophila is present worldwide, a large number of Humidophila taxa have a restricted distribution within the (sub-)Antarctic Region, showing a clear bioregionalism.

Several populations of a new Craspedostauros species were observed on museum specimens of juvenile green turtle and Kemp's ridleys collected from Long Island Beach, New York, USA. The new taxon, Craspedostauros alatus Majewska & Ashworth sp. nov., exhibits a distinctive set of morphological features typical of the genus, including cribrate areolae, a stauros narrower than the fascia, multiple doubly perforated girdle bands, and two fore and aft chloroplasts, but clearly differs from all known Craspedostauros species in possessing partially fused proximal helictoglossae forming an internal thickening with a shallow central cavity, distinctive external wing-like silica flaps near the apices, and a combination of valve dimensions and stria density not observed in other taxa. The same taxon was identified in the NCMA culture collection (strain CCMP120), isolated in 1967 from a sample collected from the equatorial upwelling zone in the Pacific Ocean. Nine samples from three sea turtle species were collected from the same location (Long Island Beach). Statistical analyses suggested that the epizoic diatom flora composition was not affected by the collection season but differed among sea turtle species. The most significant difference was observed between the samples with and without C. alatus. Samples with C. alatus were always dominated by Achnanthes elongata and Berkeleya cf. rutilans, while those lacking the new taxon were characterized by remarkably higher contributions of epizoic Poulinea species. This observation suggests that the microhabitat provided by each sea turtle differs among specimens, which may be related to the different stages of biofilm development on the host sea turtle. Additionally, the value of zoological museum collections for epizoic diatom surveys is briefly discussed.

Nagumoea livingstonensis sp. nov., a new diatom species is described from a coastal pool on the Maritime Antarctic Livingston Island, South Shetland Islands, based on light and scanning electron microscopy observations. A morphological comparison is made with the two other known Nagumoea taxa. The new species can be separated by the clear hyaline line between the valve face and mantle areolae, differences in the structure of its a scalariform valvocopula and broader fibulae. The taxonomic position of the genus Nagumoea is discussed. A placement within the Rhopalodiales is doubtful based on the absence of clover-shaped areolae coverings in Nagumoea making the order of Bacillariales a more probable position.

During a survey of the freshwater diatom flora of the sub-Antarctic region (Iles Kerguelen and Iles Crozet) in the southern Indian Ocean, an unknown Cyclotella taxon was observed that was formerly identified as the presumed cosmopolitan C. meneghiniana. Detailed morphological analysis based on light and scanning electron microscopical observations and comparison with several similar Cyclotella taxa worldwide justified the description of this unknown taxon as a new species: Cyclotella deceusteriana sp. nov. The new taxon is characterized by the presence of marginal fultoportulae on every costa, hyaline furrows between the raised marginal parts on which the striae are located, two, occasionally one or three, central fultoportulae and an entirely almost flat, smooth, a smaller central area than in most other Cyclotella species, lacking granules, short spines or other protuberances. The new species is described and compared with other Cyclotella taxa. Notes on its distribution and ecology are added.

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.

International audience; Five species of the terrestrial diatom genus Luticola D. G. Mann were found during a taxonomic survey of two small volcanic islands, Ile Amsterdam and Ile Saint-Paul (Southern Indian Ocean). Apart from the two already known Luticola species L. beyensii Van de Vijver et al. and L. subcrozetensis Van de Vijver et al., two new species are described: L. ivetana Chattova and Van de Vijver sp. nov. and L. vancampiana Chattova and Van de Vijver sp. nov. Finally, one, up to now unknown, Luticola species is briefly discussed and illustrated. Detailed morphological descriptions of these taxa are provided based on both light and scanning electron microscopy observations. Morphological features of the new species are compared to morphologically similar taxa, and notes on their ecology and biogeography are added.

Two Mastogloia Thwaites ex W.Sm. taxa were found during a survey of the diatom flora of Lac de Guiers, Senegal. Based on all currently available literature, one taxon could be identified as M. belaensis M.Voigt, a species formerly described from Pakistan. The second species showed some resemblance to M. braunii Grunow. Analysis of the type of M. braunii revealed, however, important morphologic differences, leading to the description of a new species from the Senegal population: M. senegalensis Van de Vijver, Fofana, Sow & Ector sp. nov. The present paper describes this new species and discusses and illustrates the morphology of M. belaensis and the type of M. braunii. All taxa are discussed with morphologically similar taxa.

The identity of Navicula brasiliana (Cleve) Cleve is here detailed based on analysis of the original slide from the Cleve & Möller collection. Additional observations with light and scanning electron microscopy of two later varieties described from the Neotropics are also provided: N. brasiliana var. platensis Frenguelli and N. brasiliana var. guadalupensis Manguin described from Argentina and Guadalupe (French Antilles), respectively. Based on the morphological characteristics of the frustules the three taxa belong to Cosmioneis D.G. Mann & Stickle. These rather rare taxa are usually reported from fresh to brackish water environments, including hot springs in the Neotropical and Paleotropical regions. While N. brasiliana var. platensis is widely recorded in several regions of the African continent and Argentina, N. brasiliana is often recorded in Central America, almost certainly because of uncertainty over their identities, to date based only on line drawings. We conclude that Cosmioneis brasiliana (Cleve) C.E. Wetzel & Ector comb. nov. is a distinct species, while N. brasiliana var. guadalupensis is a taxonomic synonym of Cosmioneis platensis (Frenguelli) C.E. Wetzel, E. Sar & Ector comb. nov. Fil: Wetzel, Carlos E.. Luxembourg Institute of Science and Technology; Luxemburgo Fil: Sar, Eugenia Alicia. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Ficología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Sunesen, Inés. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Ficología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Van de Vijver, Bart. Universiteit Antwerp; Bélgica. Botanic Garden Meise; Bélgica Fil: Ector, Luc. Luxembourg Institute of Science and Technology; Luxemburgo

International audience; Diatom and water chemistry samples were collected during the austral summer of 2007 from lakes, streams and bogponds on Ile Amsterdam (TAAF), a small island located in the southern Indian Ocean. A diverse diatom flora of 104 taxa was found, dominated by several Pinnularia taxa, Frustulia lebouvieri, Kobayasiella subantarctica, Eunotia paludosa, E. muscicola and Planothidium subantarcticum. Biogeographically, the Ile Amsterdam freshwater diatom flora is composed of cosmopolitan, sub-Antarctic and endemic elements. The biogeographical analysis showed that almost 17% of all observed taxa can be considered endemic to Ile Amsterdam with an additional 14% showing an exclusive sub-Antarctic distribution. The flora can be considered as typical for oceanic islands based on its disharmonic composition with several genera lacking and other being overrepresented. Canonical Component Analysis was used to classify the samples based on their chemical characteristics, revealing that, specific conductance, sulphate and pH were the main factors dividing the samples into four different groups. The geological history of the island in combination with the climate and the specific environmental features of the main habitat in the Caldera most likely shaped the composition of the actual diatom communities.

During a survey of the limno-terrestrial diatom flora of the sub-Antarctic region, two unknown melosiroid diatom taxa were observed in several shaded, damp cave (moss and soil) samples from Heard Island and Ile de la Possession, the main island of the Crozet Archipelago. Comparison with already known species from the genus Melosira and the recently described genera Arcanodiscus, Angusticopula and Ferocia, resulted in the description of both new taxa based on detailed light and scanning electron microscopy. A first species was described as Ferocia subantarctica sp. nov. and can be distinguished based on its numerous, narrow girdle bands, relatively weakly domed valves, a limited number of well-developed spines and a rather large, hyaline central area. The second species, Arcanodiscus desmetianus Van de Vijver sp. nov., can be recognized based on its solitary frustules, a series of parallel ridges surrounding the mantle and a hyaline central area that is only less than 50% of the total valve diameter. Both taxa are morphologically and ecologically characterized and compared with all known melosiroid taxa worldwide.

Two new Geissleria species are described from Portugal based on their morphological and ultrastructural characteristics. Geissleria tagensis Novais et Ector sp. nov. has rhombic-elliptical valves with broadly rounded to slightly protracted apices and lacks an isolated pore. Geissleria lusitanica Novais et Ector sp. nov. has linear-elliptical to elliptical valves with slightly to markedly protracted ends and two isolated pores. The type analysis of similar species (Geissleria acceptata (Hustedt) Lange-Bertalot et Metzeltin, G. schoenfeldii (Hustedt) Lange-Bertalot et Metzeltin and Navicula modica Hustedt) allowed their better characterization and illustration, supporting the delimitation of the new Portuguese species. A new taxon present in the type material of G. schoenfeldii, G. hinziae Novais et Ector is also described. Three new combinations are also proposed: Geissleria capitata (H. Kobayasi in Kobayasi et Ando) Ector et Novais comb. nov., G. modica (Hustedt) C.E. Wetzel, Novais et Ector comb. nov. and G. taishanica (Y.Q. Guo et S.Q. Xie) Ector et Novais comb. nov. A checklist of the species and a thorough survey of the literature available on Geissleria are provided.

The ultrastructure of Gomphonema gautieri (Van Heurck) Lange-Bert, et Metzeltin was studied based on a small population from a small Swedish, slightly acid, eutrophic river. The observations were compared with the holotype slide of G. augur var. gautieri Van Heurck, as the species was originally described in 1885. The valves are characterized in having a typical clavate outline with the largest width near the broadly rounded headpole. The species can be separated from G. augur Ehrenb. by its larger valve dimensions, the presence of broad shoulders on the headpole and the lower number of areolae per stria. Based on these differences, a separation of both taxa is justified.

The analysis of a sample taken in a lava tube cave on Île Amsterdam (southern Indian Ocean) revealed the presence of three interesting small-celled naviculoid diatom taxa. Based on light and detailed scanning electron microscopy, two of these taxa are described as new: Mayamaea cavernicola sp. nov. and Sellaphora barae sp. nov. A third taxon, Chamaepinnularia aerophila Van de Vijver et Beyens, was previously only found in the type locality on the nearby Crozet Archipelago. The three taxa are compared to other morphologically similar species from Europe, South America and the (sub-)Antarctic Region.

During a survey of the freshwater diatom flora of the sub-Antarctic Kerguelen archipelago in the southern Indian Ocean, an unknown Diatomella taxon was observed forming long colonies using linking spines. Detailed morphological analysis based on light and scanning electron microscopical observations and comparison with all known Diatomella taxa worldwide justified the description of this unknown taxon as a new species: Diatomella colonialis sp. nov. The new taxon is characterized by the presence of marginal linking spines, the reduction of its raphe structure leaving only two short raphe slits near the apices, a very large axial area occupying almost the entire valve face and very short alveolate striae composed of paired areolae. The presence of these alveolate striae and the girdle structure with its typical scalariform valvocopula place this taxon in the genus Diatomella. The new species is described and compared with other Diatomella taxa. Notes on its distribution and ecology are added.

During a survey conducted on the soil diatom flora of newly exposed areas due to the retreat of the Ecology Glacier (King George Island, South Shetlands) an unknown Muelleria taxon was observed that could not be identified using the currently available literature. Based on detailed morphological observations using LM and SEM microscopy the unknown taxon has been described as new for science - Muelleria olechiae sp. nov. The new species is characterized in having typically bifurcated terminal raphe fissures, elongated, deflected proximal raphe endings and a lack of canal puncta. It was observed in several soil samples, but always in relatively low abundances.

During a survey of the freshwater aquatic diatom flora of two peat bog areas in Tierra del Fuego, southern Argentina, a new taxon belonging to the genus Stauroneis that could not be identified was observed. Based on detailed light and scanning electron microscopy observations and comparison with similar larger-celled Stauroneis species worldwide, the taxon is described as new: Stauroneis fuegiana Casa & Van de Vijver sp. nov. Stauroneis fuegiana can be distinguished based on the slightly raised marginal crest, the typical broadly lanceolate valve outline with subrostrate apices, the almost rectangular central area and its valve dimensions. Comments are made on its taxonomic position and how the new taxon can be distinguished from other larger-celled Stauroneis species. Brief notes on the ecology and distribution are added. Fil: Casa, Valeria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín; Argentina Fil: Mataloni, Maria Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín; Argentina Fil: Van De Vijver, Bart. Botanic Garden Meise; Bélgica. Universiteit Antwerp; Bélgica

A new centric diatom genus, Ferocia Van de Vijver & Houk gen. nov. is described based on Melosira setosa Greville. Several samples collected in lava tunnels on Ile Amsterdam, a small isolated, volcanic island in the southern Indian Ocean where the latter taxon dominated the diatom flora, were investigated. The new genus is characterized by having heavily silicified, spherical frustules, connected into long chains by large, complex linking spines. Valves are dome-shaped with a high mantle with rounded to irregularly shaped areolae. Numerous small rimoportulae forming a marginal ring are present near the mantle edge. The cingulum is composed of a large number of narrow, open copulae. A second species, Ferocia ninae Van de Vijver & Houk sp. nov., is described from the nearby Crozet archipelago. Besides the typical features of the genus Ferocia, the rimoportulae in F. ninae are almost equidistant, the valves have a relatively low valve height and the spines are relatively small. Both F. ninae and F. setosa were found in shaded lava tunnels with a sparse moss vegetation. The two species are illustrated and discussed based on detailed LM and SEM observations.

Recent morphology-based studies indicate that freshwater diatom floras in the Antarctic comprise a significant share of endemics among a majority of apparently cosmopolitan species. Given the widespread (pseudo)cryptic species diversity in diatoms, we assessed the molecular divergence and temperature-dependent growth characteristics between Antarctic and non-Antarctic strains for two presumed species with a cosmopolitan distribution, namely Pinnularia borealis and Hantzschia amphioxys. Molecular phylogenies based on the plastid gene rbcL and the nuclear 28S rDNA (D1-D3 region) revealed that both taxa consist of multiple lineages, each including a distinct Antarctic lineage. A molecular clock estimates the origin of P. borealis at 35.8 (30-47) million years (Ma) ago, making this the oldest known diatom species complex. The Antarctic P. borealis lineage is estimated to have diverged 7.8 (2-15) Ma ago, after the geographical and thermal isolation of the Antarctic continent. Despite not being psychrophilic, the Antarctic lineages of P. borealis and H. amphioxys have a lower optimal growth temperature and upper lethal temperature than most lineages from more temperate regions, indicating niche differentiation. Together, this suggests that many presumed cosmopolitan Antarctic diatom species are in fact species complexes, possibly containing Antarctic endemics with low temperature preferences.

Four monoraphid taxa belonging to the genera Achnanthes, Psammothidium and Planothidium were found during the ongoing taxonomic revision of the freshwater and limno-terrestrial diatoms of the Maritime Antarctic region. The present paper describes these four taxa as new based on detailed light and scanning electron microscopy observations: Achnanthes kohleriana Kopalová, Zidarova & Van de Vijver sp. nov., Planothidium wetzelectorianum Kopalová, Zidarova & Van de Vijver sp. nov., Psammothidium confusoneglectum Kopalová, Zidarova & Van de Vijver sp. nov. and Psammothidium superpapilio Kopalová, Zidarova & Van de Vijver sp. nov. The morphology and ecology of all four taxa are discussed and the species are compared with morphologically similar taxa.

A revision of taxa from the genus Surirella from the Antarctic region resulted in the description of three new taxa: S. subantarctica Van de Vijver & Cocquyt sp. nov., S. heardensis Van de Vijver & Cocquyt sp. nov. and S. australovisurgis Van de Vijver, Cocquyt, Zidarova & Kopalova sp. nov. Detailed light (LM) and scanning electron microscope (SEM) observations are used to characterize these three new taxa. Comparisons with similar taxa and the ecological preferences of each species are added. The morphological characteristics of a fourth Antarctic Surirella taxon, S. kerguelensis Grunow are illustrated as this taxon was only known from a few hand drawings and LM pictures. Finally, a fifth taxon, S. lapponica A. Cleve was found on South Georgia and likewise illustrated. The revision of these species made clear that the genus Surirella showed similar biogeographical trends as other, previously revised genera indicating that a distinct Antarctic diatom flora exists.

A new benthic freshwater diatom species belonging to the genus Pinnularia Ehrenb. has been recorded in the Agua Forte stream surrounding the Aljustrel mining area in southern Portugal. Pinnularia aljustrelica Luis, Almeida et Ector sp. nov. is described as a new species based on light and scanning electron microscopy observations and on its particular habitat in an acidic environment due to acid mine drainage, high metal concentrations (As, Cd, Cu, Fe, Mn, Pb and Zn) and high sulphate and conductivity. The taxa most similar to P. aljustrelica are P. acidophila Hofmann et Krammer, P. acoricola Hustedt and P. acoricola var. lanceolata Hustedt, so type materials of these taxa were studied for comparative purposes. Although, the ecology of the three similar taxa is also quite similar, the new species has a combination of particular morphological characteristics studied under LM and SEM that separates it from the rest. Pinnularia aljustrelica has a general shape relatively similar to P. acidophila and P. acoricola, but the valve outline is not as linear as in P. acidophila and not as oval as in P. acoricola.

During the ongoing revision of the non-marine diatom flora of Livingston Island (South Shetland Islands, Maritime Antarctic Region) the taxonomy and morphology of all Pinnularia taxa, excluding the section Distantes , present in the samples from Livingston Island, have been analysed. Seventeen different Pinnularia taxa have been recorded. Apart from those previously described from the Antarctic Region ( P. subcapitata var. elongata , P. gemella , P. austroshetlandica ) and the Andes ( P. strictissima ), thirteen unknown taxa have been found. Based on their unique morphological features, twelve are described as new in this paper: P. australodivergens sp. nov., P. australoglobiceps sp. nov., P. australomicrostauron sp. nov., P. australoschoenfelderi sp. nov., P. hamiltonii sp. nov., P. livingstonensis sp. nov., P. magnifica sp. nov., P. microstauroides sp. nov., P. pseudolaucensis sp. nov., P. sergiplaiana sp. nov., P. subcarteri sp. nov. and P. subaltiplanensis sp. nov. For one, only a few specimens have been found and at present they cannot be identified with 100% certainty.

As part of a study on the diatom flora of the Gokyo Valley, Everest National Park, Nepal, eleven species of Cymbopleura (Bacillariophyta), including two new species, Cymbopleura gokyoensis juttner et V an de V ij V er sp. nov. and Cymbopleura emoda juttner et V an de V ij V er sp. nov., were investigated using light and electron microscopy. Some taxa could not be identified with certainty using the currently available literature due to small differences in valve dimensions, raphe structure and striation patterns. It remains unclear whether they represent new species or whether the original descriptions should be emended to include the populations from Nepal.

Van de Vijver B., Zidarova R., Sterken M., Verleyen E., de Haan M., Vyverman W., Hinz F. and Sabbe K. 2011. Revision of the genus Navicula s.s. (Bacillariophyceae) in inland waters of the Sub-Antarctic and Antarctic with the description of five new species. Phycologia 50: 281–297. DOI: 10.2216/10-49.1 A revision of the diatom genus Navicula s.s. in inland water samples from the Sub-Antarctic and Antarctic resulted in the description of five new species, viz. Navicula australoshetlandica Van de Vijver sp. nov., N. dobrinatemniskovae Zidarova & Van de Vijver sp. nov., N. cremeri Van de Vijver & Zidarova sp. nov., N. conveyi Van de Vijver sp. nov. and Navicula bicephaloides Van de Vijver & Zidarova sp. nov. The new species are extensively compared with other similar species. The morphology and taxonomy of three other Navicula taxa present in the same materials are briefly discussed. A critical revision of literature reports of Navicula taxa in the Antarctic and Sub-Antarctic region indicates that de...

Representatives of the Achnanthidium minutissimum (Kutz.) Czarn. complex are common and widespread diatoms in Poland. The following species were included in this study: Achnanthidium affine (Grunow) Czarn., A. caledonicum (LanGe-Bert.) LanGeBert., A. eutrophilum (LanGe-Bert.) LanGe-Bert., A. exile (Kutz.) HeiB., A. jackii raBenH., A. lineare w. Sm., and A. minutissimum. Two additional species are here formally described, namely Achnanthidium polonicum Van de VijVer, wojtaL, e. moraLeS et eCtor and A. acsiae wojtaL, e. moraLeS, Van de VijVer et eCtor. Information for an additional taxon is presented here, but it has been left unidentified until a larger population is found. Results of morphological analyses performed with light and scanning electron microscopy on this group of diatoms inhabiting springs, streams, rivers and lakes in southern Poland are illustrated and briefly discussed. Distribution of Achnanthidium caledonicum, A. eutrophilum, A. exile, A. lineare and A. minutissimum in waters of southern Poland corresponds well with literature reports of their autecology.

Freshwater diatoms are considered to be reliable indicators of the trophic status of rivers and lakes. In the past 30 years, a number of indicator indices have been developed and used for the assessment of trophic conditions all over Europe. It is however still not clear whether the ecologic signature of diatoms differs between these indicator indices. The present study assessed a large number of published European indices on the response of freshwater diatoms to trophic conditions by evaluating the consistency in the use of taxa and their trophic score from seven European indicator indices. The STAR (Standardisations of River Classifications) diatom database, a large set of samples from European running waters, was used to test the application of trophic classifications in water quality assessment. The analysis of taxa in common within the trophic indices showed that there are considerable differences between the indices, for example in the score of trophic values. There was more agreement in classification of taxa within the oligotrophic and the hypertrophic preferences than within the mesotrophic range. Based on these results, a list of diatom taxa, that are consistently used in different trophic indices, was composed. It included 159 reliable taxa that are not sensitive to regional setting, water type and taxonomic uncertainty. The list was further accompanied by a description of the taxa's trophic preferences. The large deviation in trophic scores for a number of diatom taxa could most probably be explained by taxonomic uncertainties. Application of these taxa for trophic assessment was questionable. The test set of the 359 STAR samples showed that differences between the trophic indices also lead to a significant variation in the water quality assessment results. Although trophic indices provide an excellent biomonitoring tool, they should be applied with caution, considering the recommendations provided in this paper.

During a survey conducted on the freshwater diatom flora of small shallow pools on the Ecology Glacier forefield (King George Island, Maritime Antarctic Region), an unknown spine-bearing chain-forming Pinnularia species, belonging to the Pinnularia borealis species complex, was found. Although it closely resembles the recently described Pinnularia catenaborealis from James Ross Island and Vega Island (Antarctic Peninsula), a unique set of morphological characteristics revealed in both light and scanning electron microscopy clearly discriminates the specimens of King George Island as a new species. Pinnularia subcatenaborealis Kochman-Kędziora, Pinseel & Van de Vijver sp. nov. can be distinguished from P. catenaborealis by an overall smaller valve size, the presence of irregularly formed silica outgrowths on the mantle and small, irregular plates located near the apices. The new taxon is so far only recorded from a small pool with circumneutral pH and very low conductivity.

Nine Navicula species observed in European rivers and lakes are discussed using light and scanning electron microscopy. Four of them are described as new species: Navicula antverpiensis Van de Vijver & Lange-Bertalot sp. nov., N. wendlingii Lange-Bertalot, Hofmann & Van de Vijver sp. nov., N. lacuum Lange-Bertalot, Hofmann, Werum & Van de Vijver sp. nov. and Navicula suecicarum Van de Vijver, Jarlman & Lange-Bertalot. The taxonomy of five other, already established, taxa is investigated: Navicula neomundana(Lange-Bertalot) Van de Vijver, Jarlman & Lange-Bertalot stat. nov., Navicula simulata Manguin syn. Navicula symmetrica Patrick, Navicula schroeteri Meister s. str. and N. escambia (Patrick) Metzeltin & Lange-Bertalot. The ecological preferences and distribution for each species are briefly discussed. Navicula veneta Kutzing is formally lectotypified.