Two new benthic freshwater species belonging to the genus Achnanthidium Kützing were found in French rivers located in the Languedoc-Roussillon region. Achnanthidium barbei and A. costei are described as new species based on light and scanning electron microscopy observations. These species belong to the ‘A. minutissimum complex’ based on the short, straight distal raphe fissures. Achnanthidium barbei and A. costei were found in rivers characterized by an alkaline pH and high phosphorus. Achnanthidium costei occurs in waters with very high conductivity and sulfate. The most characteristic morphological features of A. barbei are the bent frustule with recurved apices in girdle view, clearly lanceolate valves with convex margins and distinctly protracted apices, and the presence of up to six areolae per stria. Achnanthidium costei is characterized by a linear raphe valve outline and a wide axial area on the rapheless valve. Both species are compared with the most similar species: A. caravelense Novais & Ector, A. ennediense (Compère) Compère & Van de Vijver, A. eutrophilum (Lange-Bertalot) Lange-Bertalot, A. lineare W. Smith, A. minutissimun (Kützing) Czarnecki., A. pseudolineare Van de Vijver, Novais & Ector, A. sublineare Van de Vijver, Novais & Ector and A. tepidaricola Van de Vijver & M. de Haan. The ecological preferences of both species are assessed based on physicochemical analyses carried out on sites that are part of water quality monitoring networks.
This study investigated the synthesis of photoprotective compounds by Bacillariophyceae (Porosira glacialis) in real time using a 13C tracer. Our results show a relationship between the net production rates of mycosporine-like amino acids (MAAs) and photoprotective pigments such as diadinoxanthin (DD). After 24 h, the total carbon uptake rate of P. glacialis was higher when exposed to photosynthetically active radiation (PAR) than when exposed to ultraviolet radiation (UVR). However, with time, the total carbon uptake rate and turnover rate of P. glacialis exposed to UVR increased to the point where the net production rate of MAAs under UVR was higher than that of P. glacialis exposed to PAR. The differences in MAA and DD production rates and carbon uptake indicate the production of MAA and DD as a defense strategy in response to UV-induced damage. The results of this study provide insight into the synthetic pathways of photoprotective compounds and the carbon cycle within P. glacialis cells and reveal contrasting patterns in the production of MAAs and xanthophyll compounds such as DD over time.
Neidiopsis hamiltonii sp. nov. and Neidiopsis weilandii sp. nov. are described from a stream, lakes and ponds in western North America. The new species are readily distinguished from the three other published species of Neidiopsis by valve size, valve shape and the nature of the proximal raphe ends. In both new species, loculi along the valve margins are continuous and form hollow longitudinal canals, as in Neidium. Diagnostic features common to all five Neidiopsis species include: (1) a mix of uniseriate and biseriate striae; (2) striae arranged in two offset ranks; (3) distal raphe fissures simple (not bifurcate); (4) habitat restricted to cold oligotrophic streams, lakes and ponds with low conductivity; and (5) distribution limited to the Arctic, sub-Arctic and alpine zones of temperate regions in the northern hemisphere. Considerable variation in valve shape, including apical shape, is demonstrated in Rocky Mountain populations of N. hamiltonii, N. levanderi (Hustedt) Lange-Bertalot & Metzeltin and N. wulffii (Petersen) Lange-Bertalot. A comparison of morphometric data for various populations of N. levanderi and N. wulffii indicates that valves from the Rocky Mountains tend to be larger than valves from European and more northerly North American populations.
There are many useful metrics currently available to explain ecological variation within phytobenthic communities. However, most metrics are challenging to use (requiring specialist taxonomic skills and knowledge), limiting their widespread applicability. Furthermore, because most metrics have been developed to represent ecological responses to single pressures, no single metric in isolation can effectively describe complex changes in the state of communities responding to multiple environmental pressures. Understanding of such changes therefore requires the use of multiple metrics to account for the impacts of many environmental pressures. This study explores the potential of functional and morphological classifications to explain phytobenthic community responses to differences in nutrient concentration, current velocity, simulated high flow disturbances and invertebrate grazers. Three previously used phytobenthic classifications and a new metric developed from a phytoplankton classification were tested using two datasets from streams in the north west of England in 2010. A combination of the newly applied morphological classification (using maximum linear dimension, surface area and volume) and a functional classification (using life-forms) showed great potential for aiding the understanding of phytobenthic community responses to environmental pressures. Furthermore, it is suggested that, with further testing, this new classification, which requires less specialist knowledge, could be widely implemented and would potentially give great insight into the ecology of the entire phytobenthic community.
We measured cell attachments and stalk lengths of the stalked diatom Didymosphenia geminata in situ, using in vivo staining, under different nutrient (phosphorus and nitrogen) and light treatments. Our aims were: (1) to investigate the effects of light and temperature (season) on attachment and stalk growth, including the effect of ultraviolet radiation (UVR), which has been suggested as a possible factor favouring D. geminata proliferation; and (2) to test the hypothesis that enrichment with dissolved phosphorus (DRP) inhibits the initial attachment of D. geminata cells. Although low concentrations (below ∼ 2 mg m−3) of DRP appear to be responsible for D. geminata proliferation, its general absence where DRP>2 mg m−3 is not understood. The experiments were conducted in outdoor channels over 14 months, spanning a range of water temperatures and light intensities. Increasing visible light intensity usually had a positive effect on attachment densities and stalk length, but both were depressed by very high intensities. Exposure to UVR generally led to lower attachment rates and shorter stalks. Increasing water temperature with season had a positive influence on the proportion of cell attachments producing stalks. Elevated nutrients (up to 6.6 mg m−3 P, and up to 115 mg m−3 N above ambient) did not affect D. geminata cell attachment unless the treatment channels contained previously colonised substrata. Nutrient enrichment negatively affected stalk length. Earlier findings of a positive role of light and a negative effect of nutrients on stalk length in D. geminata were corroborated, except that photoinhibition was demonstrated at very high visible light intensities. There was no evidence of a positive effect of UVR on D. geminata proliferation at the initial stages of attachment and growth. The results indicated that the absence of D. geminata from rivers with high DRP concentrations is not the result of nutrient interference with initial cell attachment.
Auxospore production was induced in clonal cultures of three morphologically similar Cyclotella species, C. meneghiniana, C. gamma and C. quillensis to determine the pattern of variation of the frustule morphology through the life-cycle. Investigations were made by light and electron microscopy. The Cyclotella species have in common the tangential undulation of the smooth central area, striated marginal area, presence of valve face and mantle fultoportulae with three satellite pores and at least one rimoportula. Each of the three species produced two size groups with slightly different valve morphology. The morphological characters of the two size groups can cause identification difficulties, especially when found together. This paper presents an interspecific comparison of the morphology of the siliceous cell wall of the initial cells and their descendants. Auxospore production was induced in a small portion of the cells 3-12 days after transfer into seawater based saline medium (7.5 parts per thousand). The initial cells showed species-specific structures and have taxonomic potential in delimitation of the Cyclotella taxa. Initial cell valves were hemispherical or domed, but cells with a relatively flat central area were found, complicating identification. The complex morphology of initial cells found in this investigation has shown that C. wulfiae is the initial cell of C. meneghiniana
While conducting surveys of freshwater algae from the Hawai'i Islands, we encountered several diatom species and populations belonging to the genus Diadesmis, subgenus Paradiadesmis. Upon closer examination of valve morphology with scanning electron microscopy, the species and populations assigned to Paradiadesmis differed considerably in structure and microhabitat fidelity from Diadesmis confervacea Kützing, the type species of the genus Diadesmis. The Hawai'i species have each stria composed of a single elongate areola, external distal raphe ends that are straight to curved, and fine hymenate occlusions on the interior of the areolae. These structures are not found in D. confervacea. Therefore, we propose a new genus, Humidophila, to accommodate these taxa formerly belonging to the subgenus Paradiadesmis. One new species from the Hawai'i Islands is described and 47 former Diadesmis species are transferred to Humidophila.
Diatom research, ISSN 0269-249X, vol. 9, nr. 1, 189-211 In spring 1990 and 1991, some weeks after ice-break, macroalgae and their epiphytes were sampled from 8 areas along the stable salinity gradient of the Baltic Sea from the southern Baltic Sea proper (0.8%) to the northern Bothnian Sea 0.5%. The macroalgal hosts included the brown alga Pilyayella littoralis (L.) Kjellm., the red alga Ceramium gobii Waern, and the green alga Cladophora glomerata (L.) Kütz. In addition, seasonal succession was studied from monthly samples throughout one growing season (March-November 1991) at one of the sampling sites (0.5% salinity). Host preference was highest in spring when the diatoms were newly colonizing the rapidly growing macroalgae, and higher in the Baltic Sea proper (higher salinity) than in the Bothnian Sea (lower salinity).
The freshwater stalked diatom Didymosphenia geminata can alter benthic community structure. However, the numbers of D. geminata that must be present to do this is not clear. Is it possible that benthic communities in streams with D. geminata are not altered? A comparison of benthic communities in two similar, adjacent streams (one with and one without D. geminata) was conducted to identify the effects of D. geminata presence on benthic community structure. An additional comparison was made below the confluence of the two streams to determine the influence of an unregulated tributary stream on the temporal and spatial patterns of potential impacts of D. geminata on benthic communities. Benthic algal biomass (chlorophyll a and ash-free dry weight) in the D. geminata stream (dominated by D. geminata and Achnanthidium spp. throughout study period) was an order of magnitude higher. High D. geminata growth altered the physical environment of the stream benthos resulting in fewer grazing invertebrates and greater densities of burrowing invertebrates such as Chironomidae and Oligochaeta. Below the confluence, benthic community structure became more similar to the non-D. geminata stream. Results show that extensive growth of D. geminata can alter benthic communities, however, an unregulated non-D. geminata tributary stream can assuage impacts and establish benthic community structure resembling the non-D. geminata tributary stream over a relatively short distance. This study provides insight into the extent and mechanisms by which growth of D. geminata affects benthic communities and helps determine the influence of tributary stream on D. geminata growth and patterns in benthic communities.
We outline, in chronological sequence, the events and findings over 25 years that have shaped our understanding of Didymosphenia geminata (Lyngbye) M. Schmidt blooms. Starting with the first appearance of D. geminata mats in streams on Vancouver Island in the late 1980s and followed years later by blooms in Iceland, South Dakota and Poland, D. geminata blooms were enigmatic for nearly 20 years. Early papers exploring whether blooms were caused by environmental change consistently failed to identify any specific factor(s) associated with their onset. Following the D. geminata outbreak in New Zealand in 2004 that seemed to result from an introduction of the species, the possibility that blooms that had previously occurred elsewhere in the world might also be explained by the introduction and movement among watersheds of a new variant with a bloom-forming tendency was touted and widely accepted. Now, however, the identification of very low soluble reactive phosphorus (SRP; below ∼2 ppb) as the proximate cause of bloom formation, has led to the more likely explanation that D. geminata blooms are the result of large-scale human intervention in climatic, atmospheric and edaphic processes that favour this ultra-oligotrophic species. In this new view, blooms of D. geminata are not simply due to the introduction of cells into new areas. Rather, bloom formation occurs when the SRP concentration is low, or is reduced to low levels by the process of oligotrophication. Mechanisms that potentially cause oligotrophication on global and regional scales are identified.
A new diatom species, Cyclotella wulfiae, is described from the brackish lake Grosser Binnensee, Germany. The new species is distinguished by its size, the concentric undulation of the valve face centre, 2-14 valve face fultoportulae scattered or organized in a ring, lack of spines, gentle angle of the valve face/mantle junction and the varied width of the internal costae, a new feature in Cyclotella. Comparison of the fine structure with the closely related species C. meneghiniana, C. gamma and C. quillensis showed that the combination of characters of C. wulfiae does not belong to any of the previously described species. C. wulfiae was found only once (July 1975) associated with abundant C. meneghiniana.
The names Mastogloia smithii Thwaites ex Smith and M. smithii var. lacustris Grunow have been attributed to a variety of related diatom morphologies, partly due to the poor availability of type material and complicated nomenclatural history. The history is detailed, clarifying the type morphologies of M. smithii and reconfirming a neglected elevation of M. smithii var. lacustris to M. lacustris (Grunow) Grunow. Populations reported as M. smithii and M. lacustris from the temperate zone (Ontario, Canada and Iowa and Michigan, USA), karstic wetlands of the subtropical Everglades (Florida, USA) and the tropics (Jamaica, Mexico and Belize) are compared with each other. Based on morphological differences including density of partecta, striae and areolae, M. calcarea sp. nov. and M. pseudosmithii sp. nov. are described from the Everglades and the Caribbean region, and a lectotype of M. smithii and a neotype of M. lacustris are designated.
In order to investigate the transcriptional regulation of light harvesting proteins in diatoms we cloned and sequenced the regions encoding the N-termini together with the respective upstream DNA stretches of 11 different fucoxanthin chlorophyll a/c binding polypeptides (FCP) of Cyclotella cryptica. The deduced N-terminal amino acid sequences almost completely matched those deduced earlier from cDNA clones. No introns were found in the regions coding for the N-terminal plastid targeting sequences or shortly downstream of them.A PLACE search for cis-acting DNA elements which are known from higher plants to be involved in the light-dependent or circadian expression of Lhc genes encoding chlorophyll a/b binding light-harvesting polypeptides in green plants resulted in the detection of several motifs. A comparative analysis with DNA stretches, upstream of the Lhc, LhcaR and Fcp genes of the green alga Chlamydomonas reinhardtii, the red alga Cyanidioschyzon merolae and the diatom Thalassiosira pseudonana, however, did not show any conservation of these elements. This indicates that green plants, red algae and diatoms most probably do not share the same conserved elements for light-regulated gene expression.Furthermore a 924 bp DNA fragment habouring a stretch of 292 bp upstream DNA and the entire Fcp6 gene was amplified from genomic DNA of Cyclotella cryptica, cloned into a modified derivative of the transformation vector pPha-T1 and expressed in the pennate diatom Phaeodactylum tricornutum. Reverse transcriptase polymerase chain reaction using RNA of the transformants as template showed that the introduced Fcp6 gene indeed was transcribed, indicating that the regulatory sequence may be generally functional in diatoms.
At the International Didymo Conference (Providence, RI,
USA, 2013), federal, state and local land managers asked for
advice from the international scientific community. Managers
need to know how to respond to nuisance growths
of Didymosphenia geminata (Lyngbye) M. Schmidt. The
appropriate management response, however, may depend
on particular geographic regions of concern.
The planktonic freshwater diatom Cyclotella comensis Grunow is widely used as an indicator of oligotrophic lake conditions. Taxonomic confusion arose with the discrimination of the morphologically similar species Cyclotella pseudocomensis Scheffler and Cyclotella costei Druart & Straub. In this study, we used morphological and molecular data to investigate the relationship between C. comensis, C. pseudocomensis and C. costei using 11 strains from eight lakes in Germany and Austria. Morphological variability was high among the three morphospecies such that they could not be separated unambiguously using morphological traits. DNA sequence analysis revealed only minor differences in 18S V4 (rbcL (cox1 (Cyclotella comensis, C. pseudocomensis and C. costei are indistinguishable on morphological and DNA sequence data, suggesting that they might comprise one taxon. However, it cannot be completely excluded that they are recently diverged, closely related species.
Techniques for assessing the freshwater diatom Didymosphenia geminata in the laboratory under controlled conditions are described. Two methods for harvesting free, unattached cells from mats, and two methods for assessing cells were developed. Free cells were harvested from mats up to 28 days old using either a static method or a shaking method. Harvested cells were then assessed using two multi-well formats: a multiple- followed by a single-cell method. The multiple-cell method was found to be a rapid screening tool for fine-tuning parameter ranges to be assessed in the single-cell assay. The single-cell method, through careful monitoring, allowed quantitative assessment of cell processes. Attachment to a substratum was observed to be critical for survival and the division of free D. geminata cells. Although cells attached readily in the multiple-cell method, the inclusion of a hydrophobic substratum was essential for attachment to occur reliably when using the single-cell method. The improvement of the single-cell method through inclusion of a hydrophobic substratum was investigated, and results with and without the substratum were compared. A temperature of 18°C was found to be more suitable than 12°C for conducting the assay and the optimal pH range for the assay was found to be 7.6 to 8.2.
Considerable resources have been invested worldwide in response to the spread of the diatom Didymosphenia geminata in rivers and streams. Considering the very low possibility of elimination of an invasive microbe, management has focused on biosecurity protocols, addressed exclusively toward the human role in dispersal (e.g. ‘check, clean dry’ campaigns and gear-washing stations for recreational users). Natural dispersal by wildlife vectors may also play an important role in the spread of D. geminata and other algal species, potentially limiting or negating the efficacy of biosecurity measures. We investigated the possibility that introduced mink (Neovison vison) may be a potential dispersal agent for D. geminata and other stream diatoms in Chilean Patagonia. Neovison were trapped near a zone of strong and persistent D. geminata blooms in the fifth order Río Simpson, and also in a fourth order upstream tributary, Río Huemules, the latter with smaller, more incipient blooms. Epibiotic D. geminata cells were identified from Neovison at Río Simpson (44% positive, average 791 cells per animal, n=18 animals), and Río Huemules (20% positive, average 40 cells per animal, n=5 animals). Many other species were also observed: 20 genera, 5683 cells per mink in Río Simpson, and 18 genera, 3605 cells per mink in Río Huemules. Navicula, Epithemia, Fragilaria and Placoneis were among the genera most frequently encountered. Neovison are known to prefer the riparian ecotone of streams of all sizes, have the capacity to travel several kilometers upstream and downstream, and possibly as far as 10 km overland to colonize new catchments. Together with an estimated survival time of 60 or more days for D. geminata in a humid environment (e.g. mink fur), Neovison represent a potentially significant factor in the colonization of upstream reaches and adjacent catchments. We comment on the potential for other wildlife vectors in Patagonia, and respective alternative patterns of short- to long-distance dispersal of diatoms in continental waters. Our results suggest that wildlife vectors should be considered in the management of D. geminata, and in the case of Neovison, integrative management of multiple invasive species, and a reassessment of conservation priorities may be necessary.
A study of modem pelagic subarctic Pacific phytoplankton has revealed the presence of three distinct species of Proboscia Sundstrom, including the type species P. alata and two new species with historical complications, P. subarctica (= Rhizosolenia alata f. curvirostris Gran) is markedly different in proboscis and valve morphology from the type species and in fact bears more resemblance to fossil members of the genus. P. eumorpha (= R. obtusa Hensen sensu Ostenfeld) resembles the austral species P. inermis, but may be distinguished easily from it by its more elongate proboscis and its less truncate valve shape. SEM observations and taxonomic discussions on both these new species are presented. Samples derived from time-series sediment traps, deployed in this region (September 1982-August 1986), have revealed strong temporal flux variations. P. alata flux represents summer-fall maxima, whereas P, subarctica is highest during spring followed by a gradual decrease towards winter.
Diatom research, vol. 6, nr. 1, 165 - 173 Investigation by SEM of the diatoms previously known as Fragilaria atomus Hustedt and Opephora schulzii (Brockmann) Simonsen showed that these species should be transferred to the genus Martyana Round.
Proliferations of Didymosphenia geminata are becoming prevalent in rivers around the globe. In the Sierra Nevada of California, Didymosphenia and other taxa that produce mucopolysaccharide stalks (e.g., Gomphoneis, Cymbella) can dominate benthic environments, particularly in the altered hydrologic and thermal regimes downstream of dams. We compared the prevalence of stalked diatoms in paired reaches, one free-flowing and the other regulated, within two Sierran river systems, the American and Feather Rivers. In the regulated reaches, short-term power generation caused daily flow fluctuations and periphyton biovolume was dominated by either Didymosphenia (where hypolimnetic releases created cool summer temperatures) or other stalked diatom taxa (where temperatures were warm). Periphyton assemblages from the unregulated sites were significantly different from the regulated reaches based on biovolume, with Gomphonema being the genus at unregulated sites contributing to the dissimilarities after accounting for the stalked genera from the regulated reaches. We evaluated the consequences of mucopolysaccharides for a large-bodied grazer, tadpoles of the foothill yellow-legged frog (Rana boylii), in a factorial experiment manipulating diet and thermal regime. At 16.6°C mean daily temperature, tadpoles lost weight (72 h relative change of−16.1±7.2%) when grazing on periphyton from a Didymosphenia-dominated site. At 19.9°C (similar to unregulated river conditions), tadpoles grazed Didymosphenia at a rate similar to tadpoles consuming higher protein control periphyton, but the former tadpoles did not grow (relative change of 4.3±5.4% vs 30.7±3.4% for control periphyton). When tadpoles were fed periphyton dominated by mucilaginous stalked diatoms other than Didymosphenia, tadpole weight loss was 21.0±9.2% (cool) and 16.6±5.6% (warm). The results illustrate that hydrologically or thermally mediated shifts in periphyton composition can have significant implications for the energy transferred to grazers.
Diatom research, ISSN 0269-249X, vol. 7, nr. 2, 313-344 Original material of Diatoma fasciculatum C. A. Agardh 1812, Diatoma tabulatum C. A. Agardh 1832, and Synedra affinis Kützing 1844, has been studied. Lectotypes are selected for Diatoma fasciculatum and Diatoma tabulatum. The type material of Diatoma fasciculatum agrees with Tabularia fasciculata (C.A. Agardh) Williams & Round 1986. The new combinations Tabularia tabulata (C.A. Agardh) Snoeijs and Tabularia affinis (Kützing) Snoeijs are proposed. +
A new species, Neidium limuae Liu & Kociolek, is described from Limu Mountain, which is located in the middle part of the Hainan Province, China. The valves of this new species have a distinct linear outline with rostrate apices. The areolae forming the striae are externally covered by volate projections that show a reticulated design. These occluding projections may be branched, bifurcate or T-shaped. A detailed description of this new species is presented, based on light and scanning electron microscope observations. This is the first report of the genus Neidium Pfitzer from this Chinese province. A short review of research studies on Neidium in China complements this study, and a checklist of Neidium taxa previously reported from China is given.
Accurate taxonomic identification provides the foundation for a number of diatom applications, such as the ecological monitoring of waters and the reconstruction of past environments. Despite significant recent developments in diatom taxonomy and phylogenetics, to date, only a few taxa have been studied extensively using a wide range of techniques. In this paper, data gained from intensive research on the morphology of live and cleaned diatom cells of two Fistulifera saprophila (Lange-Bertalot & Bonik) Lange-Bertalot strains isolated from the Gulf of Gdańsk are discussed. This study suggests that because specimens of F. saprophila have very delicate frustules prone to dissolution, the species has not been fully investigated and, therefore, a revised description is presented. Data on live cells and colony morphology, as well as interesting findings on the discrepancies between measurements of wet-mounted, dried and Naphrax-mounted diatom cells are also shown. The geographical distribution and ecological tolerance of F. saprophila is probably much wider than previously reported, but needs further investigation. The results of molecular phylogenetic analyses confirm the clear separation of Fistulifera Lange-Bertalot from Navicula Bory, also showing that its sister genera are Craticula Grunow, Eolimna Lange-Bertalot and Stauroneis Ehrenberg. Surprisingly, genera considered to have similar morphological characteristics, such as Mayamaea Lange-Bertalot and Sellaphora Mereschkowsky fall on a separate phylogenetic branch.
This addendum to "Catalogue of the diatom genera" (Fourtanier & Kociolek, Diatom Researeh, 14, 1-190, 1999) includes nomenclatural information for 93 generic names, most of which were published in the last 6 years. The data for each name include authorship, place of publication with pages on which the protologue appears, date of publication, generitype, nomenclatural status and systematic position of the genus.
This paper includes species investigated through many years starting with original material from museum collections. A great number of species in the genera Stephanodiscus Ehrenberg, Cyclostephanos Round and Cyclotella (Kutzing) Brebisson, all in the family Stephanodiscaceae Makarova, are presented with holo-, lecto- and/or neotypes, type locality and information concerning nomenclature. A typus generis is given for each genus. Errors in the literature are pointed out and corrected. Species in the genus Stephanodiscus have the characteristic fasciculate morphology, they have fultoportulae, rimoportulae with their external tubular (long or short) extension and areolae internally with a domed cribrum both on the valve face and on the mantle. The typus generis is Stephanodiscus niagarae. Species in the genus Cyclostephanos have also the fasciculate structure, the fultoportulae, but their areolae have a domed cribium only on the valve face and are flat on the mantle, their rimoportulae have only a simple external opening, often connected with a spine and a marginal alveolate structure, even though in some species weakly developed, which differentiate these species from those in the genus Stephanodiscus. The typus generis: Cyclostephanos novaezeelandiae. The genus Cyclotella includes species which have a smooth central area, none to several valve face fultoportulae, a simple alveolate marginal striation and the rimoportulae with an external round or slit-like opening, located on the mantle interrupting the ring of mantle fultoportulae. In some species complexes, however, the external opening of the rimoportula can be found on the valve face, near the valve face/mantle junction. The typus generis selected is C. distinguenda. Some other described species are transferred to the new genus Puncticulata Hakansson gen. nov. encompassing the species with an areolate central area consisting of areolae and valve face fultoportulae, in some species only fultoportulae in others only areolae, a complex alveolate striated marginal area, rimoportulae on the valve face at the end of a shortened interstriae. The Opus generis: Puncticulata comta (Ehrenberg) Hakansson comb.
Studies of Brazilian diatoms are among the oldest in Latin America. However, the history of diatomology in Brazil has only recently been explored in detail. During this time, some equivocated interpretations have been committed. One was about the nationality of Father Karl Zimmermann, recently published in Diatom Research. We are compelled to clarify this point in order to contribute to the history of diatomology in Brazil and around the world.
The so-called Oamaru Diatomite dates from approximately the Eocene–Oligocene Transition (∼34 million years ago), which is widely regarded as one of the most important climatic events of the entire Cenozoic era due to global cooling and the onset of continental-scale Antarctic glaciations. It also represents one of the richest fossil diatom deposits ever known and was first made famous owing to a series of diatom papers by Grove & Sturt. Based primarily on the collection of Sturt, supplemented by slides mounted by Grove, all curated in The Natural History Museum, we consider all 108 diatom taxa from the Oamaru Diatomite that were proposed in these seminal papers by Grove & Sturt and designate type specimens for 87 taxa that were not typified by previous workers, and for which nomenclatural types could be established. Light photomicrographs of all specimens interpreted as types are presented next to reproductions of the line drawings from Grove & Sturt publications to aid future workers on the Oamaru Diatomite, and on diatom evolution across this critical climatic phase of the Palaeogene period.
A short account of the life of Boris Vasil’evich Skvortzov (1896–1980) is presented. Some details of his background, his family and his legacy are documented. A short summary of his achievements are included.
A large local population of an unfamiliar diatom Entomoneis ornata (J.W. Bailey) Reimer was observed in a Northamptonshire (UK) canal. Its status is assessed, chloroplasts described, taxonomy outlined and some speculations about its ecology are presented.
Research on samples from the Venice lagoon was carried out to determine a suitable method for the quali-quantitative evolution of diatoms living within the sediments. From March 1994 to March 1995, surface sediment samples were collected monthly from a station located in the southern basin of the lagoon. Samples were observed using both light and scanning electron microscope. A list of the taxa found during this research is reported; counts of diatoms present in a volume of sediment were also carried out. Values for cell numbers ranged from 0.2 x 106 to 1.8 x 106 cells/cm3; higher values were recorded in spring/summer and lower values in autumn/winter. Many species belonged to the nannophytobenthos (< 30 μm), which better adapted to move among the grains of sediment than larger species. Benthic taxa, belonging to the centric group of diatoms, were also found.
An amphoroid diatom epiphytic on seagrass leaves from Hainan Province, southern China was identified as Amphora lunulata Wachnicka & Gaiser. It is characterized by a semi-elliptical valve with acute apices, ventral striae interrupted at the centre, and an axial area, which is well developed on the dorsal side but narrower at the centre, in accordance with its original description. However, as seen under the scanning electronic microscope, A. lunulata presents a combination of features that is consistent with the description of the genus Seminavis, i.e., slit-like areolae covered by hymenes, terminal fissures hooked toward the dorsal side and unornamented valvocopula. Therefore, we redefined the taxonomic status of Amphora lunulata A.H. Wachnicka & E.E. Gaiser and transferred it to the genus Seminavis. We compared the morphometric characteristics of Seminavis lunulata to those of the original description from Wachnicka & Gaiser (2007) and other taxa in Seminavis, including Seminavis atlantica M. Garcia, Seminavis eulensteinii (Grunow) D.B. Danielidis, K. Ford & D. Kennett, Seminavis heidenii D.G. Mann in D.B. Danielidis & D.G. Mann.
