Diatom

From field-collected samples, two Icelandic diatom species were studied under light and electron microscopy, resulting in a newly described species and an emended description with a nomenclatural status change. A discussion on the morphological features of these taxa and their taxonomic affinities with related species is presented. Nitzschia imae is described from Blue Lagoon, south-west Iceland. The main diagnostic criteria include the presence of two differences morphotypes, one with obtusely rounded apices and the other with slightly asymmetrical valve outline and broadly rounded apices. Additionally, we propose an emended description for Hannaea arcus var. linearis since there is no concordance between morphometric features in the protologue and the type illustration.

The Upper Paraná River floodplain is one of the few remaining non-dammed stretches in Brazil. It has a typical fluvial dynamics represented by the flood pulse and a highly complex habitat, which allows the existence and maintenance of a great biodiversity, including diatom species. As it happens in tropical lowland environments, also in this floodplain, the genus Eunotia is one of the most diverse and abundant diatom groups. Therefore, this study addresses morphologic and morphometric details of a new species and the most abundant Eunotia species in sediment cores from two wetland lakes. The morphological characteristics from each species were obtained through microscopy documentation of cell walls, and compared with other related species.

A comparison of freshwater and marine Gomphonema species has shown that the ecological separation is accompanied by a morphological one. They have only been assigned to the same genus because they all have heteropolar, cuneate cells, which are attached to the substratum by a mucilage pad or stalk. The marine taxa can be split into four clusters, each of which

Background and aims – A commonly occurring Achnanthidium species has been observed in Brazilian reservoirs. The morphological features were described based on light and scanning electron microscope observations and it is described here as A. tropicocatenatum sp. nov.

Methods – The new species was compared with the type material of morphologically similar taxa: Achnanthidium catenatum and A. minutissimum. Comparisons with the most related species based on literature were also provided. Traditional weighted-averaging approaches (WA) were applied to model ecological optima.

Key results – Morphometric analysis of the valve shape supported the taxa separation; they can be easily differentiated by the morphological and ultrastructural features, including subcapitate to capitate apices, strongly radiate striae and a prominent axial area. This new species has been found in alkaline waters with low electrolyte content.

Conclusions – Records of A. catenatum in Brazil are considered questionable because the species may have been confused with A. tropicocatenatum sp. nov.

Correct identification of diatom taxa is indispensable for diatom-based water quality studies, as well as for biotechnological applications. Biological applications of taxonomy include the identification of taxa from particular specimens. In this regard, identification keys, that use a predetermined set of characters to identify a given individual, are not commonly employed by diatom specialists due to the extreme biological diversity found in this group of microalgae. This chapter reviews previous attempts of using taxonomic keys for diatom identification, highlighting the pros and cons of the use of this and similar methods. The main morphological features found in common freshwater diatom genera are briefly presented, together with an account of the historical development of technologies used for species description.

El presente trabajo supone una contribución al conocimiento de las diatomeas dulceacuícolas españolas. Se describe la diatomea Eunotia emmae sp. nov. a partir de muestras de algas epífitas recogidas en una laguna somera oligo-mesotrófica de la provincia de León. La muestra fue tomada y procesada siguiendo los protocolos comunes para diatomeas lacustres. Las características morfológicas y ultraestructurales de este nuevo taxón se detallan e ilustran mediante imágenes de microscopía óptica y electrónica. La diagnosis diferencial con otras especies afines muestra que la combinación de caracteres de E. emmae (principalmente la forma biconvexa de la valva y un conspicuo sternum) es única. Abstract This work aims at contributing to the knowledge of Spanish freshwater diatoms. The diatom Eunotia emmae sp. nov. is described from samples of epiphytic algae collected in a shallow, oligo-mesotrophic lake from the province of Leon (Spain). The sample was taken and processed following the usual protocols for lacustrine diatoms. Morphological and ultrastructural features of this new taxon are detailed and illustrated by means of light and scanning electron microscopy images. Differential diagnosis against related species shows that the combination of features in E. emmae (mainly the presence of biconvex valves and a conspicuous sternum) is unique.

NOTE: If you need a larger pdf including plates with higher resolution, please send me an e-mail request at marco.cantonati@muse.it

Diatom assemblages were investigated in 9 springs of the Berchtesgaden National Park (carbonate substratum; north-eastern Alps, Germany), by collecting individual samples from the main substrata (stones, bryophytes, surface sediment), and measuring an extensive number of environmental variables. Overall, 104 taxa belonging to 39 genera were found. The highest number of taxa observed in any one sample was 37. The Shannon-Wiener Diversity Index varied between 1.2 and 2.4. The most frequent (counted in ≥ 4 samples) and abundant (maximum relative abundance > 5%) species were Achnanthidium minutissimum, Meridion circulare, Diatoma mesodon, Eucocconeis laevis, Navicula leistikowii, Denticula tenuis, Encyonema sublangebertalotii sp. nov., Planothidium lanceolatum, Achnanthidum pyrenaicum, Eunotia arcubus, Navicula cataracta-rheni, Rossithidium petersenii, Achnanthidum dolomiticum, Diploneis krammeri, Navicula cryptotenella, and Reimeria sinuata. The proportion of species belonging to one of the threat categories of the Red List for central Europe was 54%, and included species belonging to category 3 (“Endangered”): Eucocconeis flexella, Navicula moenofranconica, N. wildii, and Rossithidium petersenii. Two species new two science were discovered and described; one species was transferred to the genus Sellaphora (S. perhibita comb, nov.), and its ultrastructure was documented in detail. Encyonema sublangebertalotii sp. nov. resembles widely distributed species such as E. minutum and E. lange-bertalotii from which it can be distinguished by the outline (in particular the endings), dimensions, external raphe course and areolae density. Moreover, it appears to be mainly epiphytic in oligo(meso)trophic springs. Oligotrophic conditions might be important also for the second new species, Eunotia glacialispinosa sp. nov. which can be easily distinguished from similar species by its dimensions, striae and areolae density, distal raphe course, and by the presence of the characteristic spines. In Berchtesgaden it occurred exclusively in a specific spring type (seepages), and was found to develop also in comparable habitats (e.g. small dystrophic lake in a fen) by examining materials from several countries in the North of Europe. All these habitats had slightly alkaline or acidic pH but never presented ombrotrophic conditions. The comparison with a carbonate National Park located at the southern margin of the Alps (Dolomiti Bellunesi) revealed many similarities but also interesting differences mostly linked to the geographic distribution of specific spring types.

A cross-check of botanical names databases revealed the presence of 19 cases of homonymy which are hereby resolved by proposing replacement names. Most cases concern diatom genera (Bacillariophyta) names which are preoccupied by spermatophytes. While Loranthella nom. nov. (Spermatophyta, Loranthaceae) and Ochradiscus nom. nov. (Spermatophyta, Resedaceae) are proposed as new names for spermatophytes, new diatom names are proposed for genera that are currently placed in the families Amphipleuraceae, Coscinodiscaceae, Hemiaulaceae, Hemidiscaceae, Melosiraceae, Metascolionei-daceae nom. nov., Naviculaceae, Pyxillaceae, Stictodiscaceae and Surirellaceae. With one exception (i.e. Eileencoxia nom. nov.) all remaining diatom genera that are discussed in the present paper are marine and/or fossil elements. The particulari-ties of each case are briefly discussed. A total of one hundred and three new combinations are proposed.

In the Adamello-Brenta Regional Park (Trentino, Italy), the diatom communities of 30 mountain springs, 15 on crystalline and 15 on carbonate substratum, were studied between 1993 and 1996. Two of them, one from each substratum type, were sampled monthly for a more detailed investigation of seasonal changes in community structure. The diatom flora of these springs consisted of 250 diatom taxa and showed similarities with springs and headwater stream diatom communities from different geographic areas. Characteristic spring taxa (crenophiles) were present, but included mainly subdominant and rare taxa. Diatom taxa numbers were similar to those found for mountain streams with the lowest values found for stones in carbonate springs; nevertheless the community structure of epilithic and epiphytic samples was found to be similar and more or less constant over the seasons. By numerical methods, diatom communities were clearly related to a pH gradient. A group of species, located at the lower end of this gradient, is typical of anthropogenetically acidified running waters.

The species Chamaepinnularia schauppiana was described in 1996 on the basis of LM observations. An investigation of specimens using the SEM was, however, considered necessary to be completely sure about the allocation of the new species to Chamaepinnularia. These SEM observations were carried out during an investigation of materials sampled from shallow pools in the Danta di Cadore mires (south-eastern Alps, Italy). SEM micrographs allowed a detailed description of the ultrastructure (in particular, the peculiar grooves on the axial and central area, and the sub-marginal position of the silica bridges dividing the striae into two foramina), and definitively confirming the genus allocation. Moreover, useful information on habitat and substrata preference of this rather rare species was also provided.

Epiphytic diatom communities on macroalgae from Iceland coastal waters were investigated during July 2005. Ten species of seaweeds have been collected belonging to brown, red and green algae. The analysis of epiphytic diatom community was carried out under scanning electron microscopy. The epiphytic diatom abundances varied from 7 ± 5 to 7524 ± 3491 cells mm−2. Erect growth forms were the most abundant, representing

The authors present a taxonomic study of benthic diatoms collected from coastal rocks in seven northern Mediterranean sites (Italy, Spain, Greece, Turkey) in spring of 2010. An iconographic catalogue of high-quality SEM and light microscopic images, plus detailed taxonomic, nomenclatural and bibliographic information, are provided as a practical reference for further taxonomic and floristic studies on 91 plates. 120 representative diatom taxa, among them several poorly known species, selected from 23 samples, are described in terms of their abundance. The authors provide detailed information on the type material of each diatom species, a list of synonyms, a comparison of morphometric data provided in the literature (in tables) and a series of iconographic SEM-images which illustrate the taxon’s morphological variability, plus an exhaustive list of references. Nomenclature, taxonomy and systematic position of the described taxa are updated. Eight taxa are described as new to science and another seven are nomenclaturally recombined. Eight taxa are new records for the Mediterranean Sea and for five taxa Scanning Electron Microscope (SEM) images are presented for the first time.

An exhaustive reference list and indices of taxa conclude this volume and make it a valuable source of information for biologists working on benthic diatoms in general, not only of the Mediterranean region.

The present study refers to the effect of metal pollution on diatoms by describing a new form of teratology. The samples were collected in the Abrud River, located in a mining area from Romania, where an unreported type of deformity is observed in the diatoms Achnanthidium sp. pl. This kind of teratology has been found in the 20.5\% of individuals of the population and affects the cingulum, in particular to the valvocopula, by becoming markedly undulate.

The centric diatom order Thalassiosirales includes all diatoms with a fultoportula (strutted process), a feature now recognized as a synapomorphy for the lineage. Within Thalassiosirales, Thalassiosira is perhaps the most taxonomically and morphologically diverse genus, and at least two distinct morphological groups have been recognized within it. Group “A” Thalassiosira species, which include the type species, T. nordenskioeldii, have short inward and long outward extensions of the strutted processes and a labiate process on the valve mantle. Group “B” species have exceptionally long inward and reduced outward extensions of the strutted processes, and a labiate process on the valve face. We collected and cultured Thalassiosira ritscheri, which has a combination of group A and B characters. It has a labiate process on the valve face and reduced outward extensions of the strutted processes. We show for the first time that T. ritscheri has short inward, A-type extensions of the strutted processes. A phylogenetic interpretation of these conditions suggests a close relationship between T. ritscheri and the traditionally held group “B” species. Species diagnosed by the autapomorphic condition of a labiate process away from the valve mantle, including many group “B” Thalassiosira species, are transferred into Shionodiscus gen. nov.

A population of an unknown Psammothidium species (Bacillariophyta, Achnanthidiaceae) was found in core sediments collected from Cimera Lake, an oligotrophic, undisturbed mountain lake in Central Spain (Gredos mountain range). The morphology and ultrastructure of this taxon is hereby documented in detail by means of light (LM) and scanning electron (SEM) micrographs. Morphologically, the closest taxon is P. levanderi, and the type of this species is analyzed here to provide a differential diagnosis. A comparison with other similar small Psammothidium species with an elliptic outline show that the combination of features exhibited by this taxon is unique and it is thus described here as Psammothidium toroi sp. nov.

... of Marine Botany, University of Goteborg, Carl Skottsbergs Gata 22, S-413 19 Goteborg, SwedenLinda K. Medlin Dept. ... The frustule is more or less straight, rectangular; the apices are slightly attenuated or produced; the corners *liman (French): silt, liman (Russian): bay, gulf. ...

Las diatomeas son un grupo de algas microsc{\'{o}}picas extremadamente diversificado que viven en los ecosistemas acu{\'{a}}ticos de todo el mundo, a pesar de lo cual los estudios sobre estos organismos en la regi{\'{o}}n del Estrecho son escasos. Esta monograf{\'{i}}a presenta el primer estudio sistem{\'{a}}tico sobre las diatomeas de Ceuta, describiendo m{\'{a}}s de 250 especies encontradas durante muestreos efectuados en ambientes tanto dulceacu{\'{i}}colas como costeros. Adem{\'{a}}s de su inter{\'{e}}s taxon{\'{o}}mico y biogeogr{\'{a}}fico, las diatomeas ceut{\'{i}}es se revelan como unos excelentes bioindicadores de la calidad del agua en los ecosistemas que habitan.