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During a French biomonitoring survey of the lakes in the region Rhône-Méditerranée-Corse, a large, unknown Gomphonema taxon was observed in a lake in the vicinity of the City of Lyon (Département du Rhône, France), that could not be identified using the currently available literature. Detailed light and scanning electron microscopy investigations revealed the presence of two types of valves, one bearing a thick marginal crest and valves lacking the crest. Following comparison with similar, mostly tropical Gomphonema species, the unknown taxon is described as new: Gomphonema vancampianum sp. nov. Discriminating features of the new species include the peculiar valve shape resembling a Chinese spoon, the broad upper valve part with acuminate tip, the presence of shallow depressions in the axial area, distinctly punctate striae and the occasional presence of the marginal crest. The new species was observed in several samples collected in an oligo- to mesotrophic, calcium-carbonate rich lake with a high ecological quality.

Background and aims – Small-celled araphid diatoms form an important part of the diatom flora in our rivers and lakes. Although several of these species are frequently reported, their correct taxonomic identity is often obscured due to a lack of good knowledge of the original (type) material. Material and methods – Several historical (nineteenth century) original samples were retrieved from different European and North American diatom collections. The samples have been analysed using light (LM) and scanning electron microscopy (SEM). Key results – Staurosirella crux comb. nov., based on Ehrenberg’s Navicula crux, proved to be the oldest valid name for Staurosirella harrisonii, the latter now being considered a younger synonym. A new European species, S. neorhomboides sp. nov., is described to replace the name S. rhomboides, now considered a younger synonym of S. leptostauron. The North American populations of S. rhomboides and S. martyi differ sufficiently from the type populations and are described as new species: S. moralesii sp. nov. and S. manoyloviana sp. nov. The new combination Staurosirella informis comb. nov. is proposed for a taxon described in 1856 from the French Pyrenees as Odontidium informe. Staurosirella leptostauron turns out to be insufficiently described and is now documented for further use. Conclusion – The analysis of the original (type) material corrected several taxonomic errors and better characterised the morphology of several commonly observed Staurosirella species.

Several populations belonging to the genus Staurosirella have been observed in European rivers that were previously identified as Staurosirella pinnata. In light of the recent taxonomic revisions of the genus Staurosirella, the morphology of the unknown Staurosirella populations has been critically investigated using light and scanning electron microscopy. Following the comparison with previously described Staurosirella species, five taxa could not be identified using the currently available literature on the genus. These five taxa are described as new based on differences in valve outline; shape, size and structure of the apical pore fields; structure of the striae; and the presence, position and structure of the marginal spines. Two new species were described using historic collection material: Staurosirella binodiformis sp. nov. and Svanheurckiana sp. nov. Two new species were observed in samples from rivers in Flanders: S. marginostriata sp. nov. and S. stoksiana sp. nov. whereas a fifth species was observed in rivers from Iceland: S. jonssoniana sp. nov. All new species are compared with similar Staurosirella species worldwide. Notes are added on their ecological preferences derived from both physicochemical data and the associated diatom flora.

Background and aims – The genus Orthoseira is generally known to be typically aerophilous. Despite the worldwide occurrence of the genus, most of the Orthoseira species seem to have a rather restricted biogeographic distribution, often being part of an endemic diatom flora. During a survey of the aerophilic diatom flora in Papua New Guinea (Karkar Island, Boisa Island), four morphologically distinct Orthoseira taxa have been observed. Material and methods – The morphology of four Orthoseira species was investigated in detail using light microscopy (LM) and scanning electron microscopy (SEM). Key results – The morphology of all four species is discussed and compared to known species worldwide. The main differences between the species include: the presence and shape of linking structures, the number of rows of perforations on the copulae, presence/absence of internal caverns and the external structure of the carinoportulae. Two species, with a unique set of features, are described as new to science: Orthoseira iserentantii sp. nov. and Orthoseira papuensis sp. nov. Conclusions – The observation of four Orthoseira species, including two species new to science, confirms that the diversity of the genus Orthoseira is underestimated.

Abstract Our understanding of the importance of microbiomes on large aquatic animals—such as whales, sea turtles and manatees—has advanced considerably in recent years. The latest observations indicate that epibiotic diatom communities constitute diverse, polyphyletic, and compositionally stable assemblages that include both putatively obligate epizoic and generalist species. Here, we outline a successful approach to culture putatively obligate epizoic diatoms without their hosts. That some taxa can be cultured independently from their epizoic habitat raises several questions about the nature of the interaction between these animals and their epibionts. This insight allows us to propose further applications and research avenues in this growing area of study. Analyzing the DNA sequences of these cultured strains, we found that several unique diatom taxa have evolved independently to occupy epibiotic habitats. We created a library of reference sequence data for use in metabarcoding surveys of sea turtle and manatee microbiomes that will further facilitate the use of environmental DNA for studying host specificity in epizoic diatoms and the utility of diatoms as indicators of host ecology and health. We encourage the interdisciplinary community working with marine megafauna to consider including diatom sampling and diatom analysis into their routine practices.

During a survey of the marine benthic diatom flora on the coasts off Livingston Island (South Shetland Islands, Maritime Antarctic Region), two Halamphora species that could not be identified based on the currently available literature, were observed. Detailed light and scanning electron microscopy observations and thorough comparison with similar taxa in the literature revealed that both taxa should be described as new species. The first taxon, Halamphora kenderoviana sp. nov., was most likely misidentified in past Antarctic studies, and included within the range of another taxon, Halamphora coffeaeformis. Analysis of literature data showed that the second new taxon, Halamphora moncheviana sp. nov., has been previously reported from the Antarctic Continent (but as an unidentified species). The new taxa are compared with similar Halamphora taxa worldwide. Data on their ecology and distribution are also provided.

Background and aims – The past two decades, the non-marine diatom flora in the sub-Aantarctic region has been intensively revised. Historic collections provide excellent tools for answering taxonomic, community-related, and biogeographical questions. This study analysed the moss-inhabiting diatom flora from sub-Antarctic Campbell Island in samples collected in 1969–1970 and retrieved from the British Antarctic Survey herbarium (Cambridge, UK). With this study we attempt to expand our, till now sparse, knowledge on the moss-inhabiting diatom flora in the southern Pacific Ocean.Material and methods – In total, the diatom composition in 32 moss samples has been analysed using Light Microscopy (LM) and Scanning Electron Microscopy (SEM). A biogeographical analysis and community analysis of the Campbell Island diatom flora were conducted.Key results – Analysis of the Campbell Island diatom flora revealed the presence of 141 taxa belonging to 45 genera. The species composition in the dominant genera Planothidium, Humidophila, and Psammothidium, the presence of Epithemia, Rhopalodia, Cocconeis, uncommon in the sub-Antarctic region, and many unidentified taxa point to the uniqueness of the Campbell Island diatom flora. The biogeographical analysis showed an overall low similarity with the other sub-Antarctic and the Maritime Antarctic islands. Four different diatom assemblages were distinguished following the community analysis. Moisture level and habitat type seem to be the main factors shaping the Campbell Island diatom assemblages.Conclusion – The results of the Campbell Island diatom analysis highlight the importance of historic herbarium material. Since the examined flora is largely composed of unknown (presumably new) species, it is vital to analyse additional (historic) samples to complete the assessment of the moss diatom assemblages from Campbell Island.

Background and aims – Despite the ongoing taxonomical revision of the entire (sub)-Antarctic diatom flora, our knowledge on the ecology and community associations of moss-inhabiting diatoms is still rather limited. In the present study, our research aim was to survey the diversity together with the environmental factors structuring the epiphytic moss diatom communities on Ile Amsterdam (TAAF), a small volcanic island in the southern Indian Ocean.Material and methods – A morphology-based dataset and (physico)chemical measurements were used for the ecological and biogeographical analysis of moss-inhabiting diatom flora from Ile Amsterdam. In total, 148 moss samples were examined using light microscopy.Key results – The analysis revealed the presence of 125 diatom taxa belonging to 38 genera. The uniqueness of the Ile Amsterdam diatom flora is mainly reflected by the species composition of the dominant genera Pinnularia, Nitzschia, Humidophila, and Luticola, with a large number of unknown and often new species. This highly specific diatom flora, together with differences in the habitats sampled and the isolated position of the island, resulted in very low similarity values between Ile Amsterdam and the other islands of the Southern Ocean. From a biogeographical point of view, 40% of the taxa have a typical cosmopolitan distribution, whereas 22% of all observed species can be considered endemic to Ile Amsterdam, with another 17% species showing a restricted sub-Antarctic distribution. The NMDS analysis, based on a cluster dendrogram, divides the samples into six main groups. For each group, indicator species were determined. Both environmental data and diatom distributions indicate that apart from elevation, specific conductance, pH, and moisture are the major factors determining the structure of moss-inhabiting diatom communities on Ile Amsterdam.Conclusion – The isolated geographic position and unique climatological and geological features of the island shaped the presence of a unique diatom flora, characterised by many endemic species. The results of the study are of prime importance for further (palaeo-)ecological and biogeographical research.

Background Ice-free areas in the Antarctic region are strongly limited. The presence of marine mammals and birds in those areas influence soil properties and vegetation composition. Studies on the terrestrial diatom flora in soils influenced by sea birds in the Maritime Antarctic region are scarce. Methods Samples were collected from two transects on the western shore of the Admiralty Bay region. Light and scanning electron microscopic observations and statistical analyses were conducted to consider the impact of penguin rookeries on soil diatom assemblages. Results The disturbance associated with the presence of penguin rookeries clearly influences the soil diatom diversity. Assemblages from areas with the highest nutrient input were characterized by a much lower diversity with only few species dominating the flora. One of recorded taxa could not be assigned to any of the known species. Therefore, based on the combination of morphological features analyzed using light and scanning electron microscopes and comparison with similar taxa in the Antarctic region and worldwide, the species is described hereby as new to science–Luticola kaweckae sp.nov. The new species is characteristic for soil habitats with strong penguin influence.

It is generally thought many microbes, owing to their ubiquity and dispersal capability, lack biogeographic structuring and clear speciation patterns compared to macroorganisms. However, Pinseel et al. demonstrate multiple cycles of colonization and diversification in Pinnularia borealis, a rare biosphere soil diatom.

Background and aims – During a survey of the soil diatom flora of the sub-Antarctic islands in the southern Indian Ocean, an unknown small-celled naviculoid taxon was discovered living in small cracks in cliffs bordering the ocean. The taxon showed a set of morphological features only found in the genus Microcostatus. However, the unknown taxon could not be identified using the currently available literature. Methods – Using both light microscopical and scanning electron microscopical techniques, the morphology of the unknown Microcostatus taxon was documented. The new taxon is described, illustrated and compared with all other similar Microcostatus taxa worldwide. Key results – Microcostatus elisabethianus possesses a unique combination of morphological features that excludes conspecificity with all other members of the genus. It is characterized by a lanceolate valve outline with protracted, elongate apices, a very large, porous conopeum reaching the valve margins and uniseriate striae composed of only one macroareola and mantle areolae restricted to the valve apices. The morphological features of the genus Microcostatus are evaluated and discussed. Notes on the occurrence and ecology of the new taxon are added.

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.

Background and aims – A few years ago, a new survey started of the freshwater diatom flora from peatbogs of Tierra del Fuego (southern Argentina). During this survey, an unknown fragilarioid diatom belonging to the genus Distrionella that could not be identified using the currently available literature was discovered.Methods – Using both Light Microscopical and Scanning Electron Microscopical techniques, the morphology of the unknown Distrionella species has been analysed. The new taxon is properly described, illustrated and compared with all other possible similar Distrionella taxa, known worldwide.Key results – Distrionella coxiana possesses a unique combination of morphological features that excludes conspecificity with all other members of the genus; it is characterized in having narrow, linear valves with small, capitate apices. Transapical ribs, a typical feature of the genus Distrionella, are only weakly developed. One rimoportula is observed close to the apices. Both apices have well-developed apical porefields. The girdle bands bear one complete row of poroids often accompanied by a second, incomplete row of small poroids. Notes on the occurrence and ecology of the new taxon are added.

Background and aims – An increased interest in the diatom flora from subaerial habitats in the Republic of North Macedonia has revealed the presence of a large number of interesting and often unknown, species. During a recent biodiversity survey, seven Muelleria species were recorded, several of which could not be identified based on the available literature.Methods – Using both Light Microscopy and Scanning Electron Microscopy techniques, the morphology of several Muelleria species has been analysed. The morphology of all taxa is described, illustrated and compared with other possible similar Muelleria taxa, known worldwide.Key results – Four already documented Muelleria species, M. gibbula, M. islandica, M. terrestris and M. undulata (= Navicula gibbula f. undulata) were identified, while two distinct species are described as new. These new species belong to the M. gibbula complex, and can be differentiated by valve size, stria density, shape of the proximal raphe ends and the shape of external areola foramina. The identity of one taxon remains uncertain due to a low number of observed specimens in the samples. As their ultrastructure is almost entirely unknown, they are briefly discussed.Conclusions – The diversity of Muelleria in Europe and the North Hemisphere is most likely underestimated and some of the previous records of M. gibbula belong to other species. Observations of diatoms from “extreme” habitats such as intermittent ponds, wet mosses and soils can reveal the existence of interesting and new species.

Background and aims – During phytoplankton surveys of a freshwater pond in Northeastern France, Fragilaria subconstricta (Bacillariophyceae) was observed. This rare diatom was present in large numbers in several plankton samples from Lachaussée Pond in the French Grand Est region.Methods – The morphology of Fragilaria subconstricta was examined in detail using light and scanning electron microscopy. Its identity is discussed and it is compared to the morphologically most similar species, especially Fragilaria capucina, F. mesolepta Rabenhorst, F. neointermedia and F. tenuistriata.Key results – Fragilaria subconstricta produces ribbon-like colonies and has narrow linear-lanceolate valves with slightly rostrate ends. The central area is rectangular, usually small or even absent. Spatulate linking spines are present all along the valve margins and a single rimoportula is located near one apex at the valve face-mantle junction. An amended diagnosis and new synonyms are proposed for this species. Additionally, the type material of Fragilaria mesolepta and a population of the very rare species Fragilaria capucina have been investigated and illustrated.Conclusions – Fragilaria subconstricta and F. tenuistriata are synonyms. Fragilaria capucina s. str. is a rare species in Europe, and the majority of records for this species should be considered part of the Fragilaria capucina “Sippenkomplex” sensu Krammer & Lange-Bertalot (1991).

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.

Biogeographic patterns of globally widespread species are expected to reflect regional structure, as well as connectivity caused by occasional long-distance dispersal. We assessed the level and drivers of population structure, connectivity, and timescales of population isolation in one of the most widespread and ruderal plants in the world — the common moss Ceratodon purpureus. We applied phylogenetic, population genetic, and molecular dating analyses to a global (n = 147) sampling data set, using three chloroplast loci and one nuclear locus. The plastid data revealed several distinct and geographically structured lineages, with connectivity patterns associated with worldwide, latitudinal “bands.” These imply that connectivity is strongly influenced by global atmospheric circulation patterns, with dispersal and establishment beyond these latitudinal bands less common. Biogeographic patterns were less clear within the nuclear marker, with gene duplication likely hindering the detection of these. Divergence time analyses indicated that the current matrilineal population structure in C. purpureus has developed over the past six million years, with lineages diverging during the late Miocene, Pliocene, and Quaternary. Several colonization events in the Antarctic were apparent, as well as one old and distinct Antarctic clade, possibly isolated on the continent since the Pliocene. As C. purpureus is considered a model organism, the matrilineal biogeographic structure identified here provides a useful framework for future genetic and developmental studies on bryophytes. Our general findings may also be relevant to understanding global environmental influences on the biogeography of other organisms with microscopic propagules (e.g., spores) dispersed by wind.

During a survey of the moss-inhabiting diatom flora of the sub-Antarctic Campbell Island, located in the southern Pacific Ocean, several unknown centric diatoms were observed that could not be identified using the currently available literature. Detailed light and scanning electron microscopical observations and comparisons with the characters of several species of Melosira, Angusticopula, Ferocia and Arcanodiscus worldwide indicated that five of them should be described as new to science: Angusticopula cosmica Goeyers & Van de Vijver sp. nov., Arcanodiscus crawfordianus Goeyers & Van de Vijver sp. nov., A. indistinctus Goeyers & Van de Vijver sp. nov., A. saundersianus Goeyers & Van de Vijver sp. nov. and Ferocia houkiana Goeyers & Van de Vijver sp. nov. A sixth species, Angusticopula chilensis, was illustrated for the first time using SEM and as a result is considered to differ sufficiently from A. dickiei to warrant epitypification as A. chilensis. The new species were first described in genera that formerly were included within the genus Melosira. All six species are morphologically characterized and compared with similar species within their respective genera. Their presence and distribution on Campbell Island are discussed based on the observations made in the available samples.

Background and aims – The Arthoniaceae form a species-rich family of lichenized, lichenicolous and saprophytic fungi in the order Arthoniales. As part of taxonomic revisions of the African Arthoniaceae, a number of species assignable to the genus Synarthonia were collected and sequenced. The present study aims at placing the genus in a phylogeny for the first time and at clarifying its circumscription. Methods – Nuclear (RPB2) and mitochondrial (mtSSU) DNA sequences from freshly collected specimens were obtained and analysed with phylogenetic Bayesian and maximum likelihood (ML) methods. Key results – Synarthonia is closely related to the genera Reichlingia and Coniocarpon in the Arthoniaceae. Six Synarthonia species are described as new to science and ten new combinations into this genus are made. A worldwide identification key to the genus Synarthonia is provided. Lectotypes are chosen for Arthonia elegans, A. inconspicua, A. lopingensis, A. ochracea, A. subcaesia and A. translucens. Arthonia thamnocarpa is synonymized with Sclerophyton elegans, and Arthonia elegans with Coniocarpon fallax. Synarthonia ochracea is shown to be a misunderstood species in the past and recent literature, since it was erroneously synonymized with Coniocarpon elegans. Synarthonia ochracea appears to start its life cycle as a non-lichenized lichenicolous fungus on Graphis before developing a lichenized thallus or it might be a facultatively lichenicolous fungus. It belongs to a complex of closely related species whose biology and circumscription are still in need of further studies.Conclusions – Synarthonia forms a monophyletic but somewhat heterogeneous lineage closely related to Coniocarpon and Reichlingia. As delimited here, Synarthonia includes corticolous lichens with a trentepohlioid photobiont as well as non-lichenized lichenicolous fungi. The core group is characterized by white pruinose ascomata, but species producing orange pruinose or non-pruinose ascomata are also included. Ascospores are transversely septate with an enlarged apical cell or are muriform. Future molecular and morphological studies are needed for a better circumscription and definition of the genus.

Epizoic diatoms form an important part of micro-epibiota of marine vertebrates such as whales and sea turtles. The present study explores and compares the diversity and biogeography of diatom communities growing on the skin and shell of loggerhead sea turtles (Caretta caretta) from four different localities: Adriatic Sea (Croatia), Ionian Sea (Greece), South Africa and Florida Bay (USA) using both light and scanning electron microscopy. We observed almost 400 diatom taxa belonging to more than 100 genera. Diatom communities from Greece and Croatia showed the highest similarity and were statistically different from those recorded from South Africa and Florida. Part of this variation could be attributed to differences in sampling techniques; however, we believe that geography had an important role. In general, contrary to several previous observations from sea turtles, the presumably exclusively epizoic diatoms contributed less than common benthic taxa to the total diatom flora, which might have been related to the loggerhead feeding behavior. Moreover, skin samples differed from carapace samples in having a distinct diatom composition with a higher proportion of the putative true epizoonts. Our results indicate that epizoic diatom communities differ according to loggerhead geographical location and substrate (skin vs. carapace). The relative abundances of common benthic diatoms and putative exclusive epizoic taxa may inform about sea turtle habitat use or behavior though detailed comparisons among different host species have yet to be performed.

Lagoons are shallow aquatic environments that typically show a broad variety in colonization by macrophytes. We present the biogenic silica (BSi) data obtained from 11 macrophyte species randomly collected in three small lagoons (Ono, Kodjoboue, and Hebe) of Ivory Coast during 12 consecutive months. BSi concentrations were different between species and between lagoons with average values ranging from 2 to 36 mg g−1. The highest values were found in Hebe and Kodjoboue lagoons due to the dominance of emergent plant species belonging to Poaceae and Cyperaceae families. However, because total plant coverage was low (5% of the lagoon surface), the total BSi stock in vegetation was low (0.2 and 6.1 t, respectively). Oppositely, lower BSi concentrations were found in plants from Ono lagoon, yet the abundance of macrophytes covered 66% of its surface area which resulted in a larger vegetation BSi stock (17.4 t). Dissolved silica in surface water varied seasonally between 1.7 and 10.8 mg L−1, and variation is assumed to be linked to diatom blooms rather than to macrophyte uptake. Sediment data showed that the three lagoons store a large quantity of BSi in their sediments with values ranging from 2 to 8 t BSi ha−1. Because of macrophyte influence in these lagoons, macrophyte phytoliths were expected to contribute significantly to this sediment BSi stock. However, microscopic analysis revealed that this stock is absolutely dominated by diatom frustules and sponge spicules rather than plant phytoliths. We conclude that macrophytes in these lagoons contribute only marginally to BSi storage in sediments but that fragile phytogenic silica structures may affect local silica cycling.

In recent years, biofilm-forming diatoms have received increased attention as sea turtle epibionts. However, most of the research has focused on carapace-associated taxa and communities, while less is known about diatoms growing on sea turtle skin. The current study investigated diatom diversity on the skin of loggerhead sea turtle heads detached from the carcasses found along the Adriatic coast between 1995 and 2004 and stored frozen for a prolonged period of time. By using both light and scanning electron microscopy we have found diatom frustules in 7 out of 14 analysed sea turtle samples. Altogether, 113 diatom taxa were recorded, with a minimum of seven and a maximum of 35 taxa per sample. Eight taxa, Achnanthes elongata, Berkeleya cf. fennica, Chelonicola sp., Licmophora hyalina, Nagumoea sp., Navicula sp., Nitzschia cf. lanceolata, and Poulinea lepidochelicola exceeded 5% of relative abundance in any one sample. The presumably obligately epizoic diatom taxa, A. elongata, Chelonicola sp., and P. lepidochelicola, dominated in six loggerhead samples, contributing up to 97.1% of the total diatom abundance. These observations suggest that on the sea turtle skin highly specialised taxa gain even greater ecological advantage and dominance over the co-occurring benthic forms than in the carapace biofilms. The suitability of frozen sea turtle skin specimens for diatom analysis and limitations of this approach are discussed.

A floristic survey was performed on a temporary pond, “Laqui du Seignavoux”, situated in the Mont-Dore massif of the French Massif Central, between 2017 and 2019. Except in 2017, each year, we performed four sampling campaigns from April/May to December. Water samples and diatoms were collected. The temporary pond evolved from a poorly mineralized ecosystem due to snow, inducing oligotrophic and oligosaprobic water, well oxygenated in spring, to a more mineralized, less oxygenated, eutrophic–hypereutrophic, and polysaprobic environment in summer. This change in abiotic conditions was found to be linked to the presence of cattle, beginning in May, that trample and excrete in the pond, leading to higher ammonium and nitrate concentrations. During this period, the dominant species were Pinnularia sp., Nitzschia palea, and Nitzschia palea var. tenuirostris. In spring and winter, different species of Eunotia dominated the community such as Eunotia pseudogroenlandica. Finally, light microscopy (LM) and scanning electron microscopy (SEM) observations on a new species of the genus Pinnularia from the temporary pond are presented and the ecological preferences are discussed.

Diatom assemblages from small pools and creeks on the Ecology Glacier forefield have been investigated. It is the first study in the Admiralty Bay region after the thorough taxonomic revision of the non-marine Antarctic diatom flora. A total of 122 diatom taxa, belonging to 35 genera were identified. More than 55% of all observed species have a restricted Antarctic distribution. Another 15% have a marine origin. Nitzschia gracilis Hantzsch, N. homburgiensis Lange-Bertalot and Planothidium rostrolanceolatum Van de Vijver et al. dominated the flora. Based on a DCA analysis, samples were subdivided in three groups reflecting ecological differences. Several samples (group 1) showed a mixed freshwater/marine diatom composition and are typical for coastal pools. Two other groups were separated based on the amount of limnoterrestrial taxa indicating the temporary character of some of the pools.

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.

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 Chattová & Van de Vijver sp. nov. and L. vancampiana Chattová & 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.

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.

Four taxa belonging to the complex of species around Achnanthidium minutissimum were found during the ongoing taxonomic revision of the Antarctic freshwater and limno-terrestrial diatom flora. Two taxa were previously described as Achnanthidium lailae and A. sieminskae. Two others were formerly identified as A. minutissimum but detailed light and scanning electron microscopical observations revealed sufficient morphological differences compared to the type of A. minutissimum, to justify their separation and description as new taxa: Achnanthidium indistinctum and A. maritimo-antarcticum. The morphology and ecology of all four taxa are discussed comparing the species with morphologically similar taxa. The biogeographical consequences of the splitting of the former A. minutissimum complex in the Antarctic Region are discussed.