Stria Density Research Articles

Non-blue Haslea species (Bacillariophyceae: Naviculaceae) in the benthic marine flora of Guam (Mariana Islands, Western Pacific Ocean).

In recent years the taxonomy of Haslea has been in flux. We describe several Haslea taxa from Guam, including four new species, in light of these recent findings. Four delicate, fusiform Haslea species are described from a variety of benthic habitats on coral reefs. These species, H. fusiformis comb. nov. and H. alexanderi, H. apoloniae and H. guahanensis spp. nov. are distinguished by stria density, foramen (‘areola’) shape, and cell size from each other and from similar taxa. A key to all these taxa is provided. In addition, an arcuate species is described as Haslea arculata sp. nov. The presence of a bilayered wall is shown for all these taxa. We compare the morphology of specimens reported as H. howeana from Guam with Navicula tsukamotoi, recently described from Okinawa, and with ‘Navicula cf. howeana’ from Puerto Rico. We provide the first account of the complex cingulum of N. tsukamotoi. We conclude that our specimens match N. tsukamotoi and that H. howeana should be returned to Navicula, but we leave open the question of conspecificity.

Envekadea vranaensis sp. nov. a new diatom species (Bacillariophyta) from the lacustrine Holocene sediments of Lake Vrana, Croatia

A new species, Envekadea vranaensis Caput Mihalić, Galović & Levkov sp. nov., is described from Holocene sediments of Lake Vrana, Croatia. The new species is characterized by linear-lanceolate valves with broadly capitate apices and is 40.0–67.5 μm long and 7.5–9.0 μm wide. Based on its morphological features it is similar to E. hedinii and E . pseudocrassirostris. Also, E. vranaensis shares morphological and ultrastructural features with E . vanlandinghamii, from which it can be differentiated by the valve outline, shape of the apices, stria density and the shape of proximal raphe endings. We present stratigraphic occurrence and ecological preferences for E . vranaensis based on associated paleoecological proxies.

Nitzschia taikiensis sp. nov. (Bacillariophyta) – a new brackish diatom from the Toberi River marsh in the eastern Hokkaido, Japan

Abstract Nitzschia taikiensis sp. nov. is a brackish diatom species found in the Toberi River marsh, eastern Hokkaido, Japan. This species has characteristics similar to Nitzschia subamphioxoides Hustedt, which was originally described by Hustedt in 1959. In the present study, we conducted a comparative morphological analysis of N. taikiensis and N. subamphioxoides. The obtained results showed that they are different species. Sampling sites of N. taikiensis were located in salt marsh environments with very low salinity (1-5‰), acidic pH (5.2-5.9) and high mud content (95.0-97.5%). Identification of this species was relatively easy based on LM and SEM image analysis of its frustule features, such as the external form and stria density. This species has not been previously reported in Japan, which could be attributed to the reduction or loss of Japanese freshwater and salt marsh environments in the coastal areas, resulting from urban and industrial development.

Encyonema keshrii, sp. nov.: A New Diatom Species (Cymbellales, Bacillariophyceae) from the Indian Subcontinent

Despite more than 150 years of diatom research in India, cymbelloid taxa have rarely been investigated when compared to the other parts of the world. A new freshwater species of Encyonema Kützing was discovered from the mountain ranges of Peninsular India and is described based on light and scanning electron microscopy observations. This paper provides a comparison of the new taxa with morphologically similar taxa of the genus Encyonema. Encyonema keshrii, sp. nov., is characterized on the basis of distinctive morphological characters including valve and apex shape as well as striae density. Enccyonema keshrii, sp. nov., is found to be a wide spread taxon with distribution across the Eastern Ghats, Western Ghats and the Eastern Himalayas of Indian subcontinent.

<p><strong><em>Cymbella hechiensis sp</em></strong><strong>. <em>nov</em>., a new cymbelloid diatom species (Bacillariophyceae) from the upper tributary of Liujiang River, Guangxi Province, China</strong></p>

During a survey of freshwater diatoms from streams in the upper reaches of the Liujiang River, Guangxi Province, China, a new Cymbella species, Cymbella liujiangensis sp. nov. was recorded. A detailed morphological description of C. liujiangensis is presented, based on light and scanning electron microscopy. The main features of C. liujiangensis include strongly dorsiventral valves with slightly truncate and obtusely rounded ends and one very large, transaspically-elongated stigma positioned on the ventral side of the central nodule and adjacent to the middle ventral striae. The new species is compared with C. dorsenotata, C. aspera, C. peraspera, C. australica, C. praerupta, C. convexa, C. crassistigmata, C. graciliformis and C. simonsenii, all of which show similarities to Cymbella liujiangensis, but differ in details of size, valve shape, striae density, puncta density, and number of stigmata.

Effect of Residual Stress on S-N Curves and Fracture Morphology of Ti6Al4V Titanium Alloy after Laser Shock Peening without Protective Coating.

In this paper, the effect of residual stress on the stress–life (S–N) curve and fracture morphology characteristics of Ti6Al4V titanium alloy after laser shock peening (LSP) without protective coating was experimentally investigated. The fatigue test and residual stress measurement were conducted on specimens before and after the LSP process. It was shown that LSP produced a high-amplitude compressive residual stress field on the surface of the specimen. After the LSP process, the fatigue life limit was increased by 16%, and the S–N curve shifted upward. Then, based on the theory of mean stress, the mechanism whereby the compressive residual stress improves the fatigue life of Ti6Al4V titanium alloy was analyzed. It indicated the improvement in fatigue life was because of the high-amplitude compressive residual stress on the surface and in depth induced by LSP to reduce the tensile stress produced by external loading. In addition, the scanning electron microscope (SEM) pattern of fatigue fracture demonstrated distinct differences in the fracture morphology before and after LSP. After LSP, the crack initiation sites of the samples moved to the subsurface where it was difficult for fatigue cracks initiating here. Moreover, after the LSP process, there were high density of fatigue striations and many secondary cracks on the fracture of the treated specimen.

Nitzschia transtagensis sp. nov. (Bacillariophyceae) from a spring in Southern Portugal

ABSTRACTA new species of Nitzschia Hassall is described from a small spring in southern Portugal. Nitzschia transtagensis sp. nov. has a unique morphology in the Lineares section, resembling Nitzschia hierosolymitana, N. vitrea and its variety salinarum. The new species is unique in that it has a convex primary (raphe) side with a slightly undulated abvalvar edge of the mantle, and a clearly undulated secondary valve side. This taxon also has a dimorphic open, ligulate cingulum composed of an apically asymmetric valvocopula having one row of roundish pores on the pars interior and attached to the valve secondary side, and two rows of pores (one of roundish and one of elongate pores) attached to the primary side of the valve. All remaining girdle elements have a single row of approximately round pores. The new species is compared to morphologically similar taxa and its ecology is discussed based on available information and literature. Additionally, it was found that a variant of the new species had been reported previously from Sardinia as “Nitzschia aff. ebroicensis”, but the Italian population has coarser stria and puncta densities.

<p><strong><em>Gomphosinica selincuoensis</em></strong><strong> <em>sp. nov</em>., a new diatom (Bacillariophyceae) from North Tibet, China</strong></p>

A new species, Gomphosinica selincuoensis sp. nov., is described from Lake Selincuo, North Tibet, China. This taxon is clearly different from the other species in genus Gomphosinica, with a distinctly protracted, rostrate headpole, relatively higher striae density, and distinctive areolae arrangement within the striae. Striae have areolae mostly in 3 rows, but there are places near the central portion of the valve and at footpole where there are only 2 rows of areolae per stria. Characteristics of this taxon, as observed in light and scanning electron microscopy, support its systematic placement in the genus Gomphosinica. This new species is compared with similar species in Gomphosinica from China and North America, and the biogeographic distribution of the genus is discussed.

Three new subaerial Achnanthidium (Bacillariophyta) species from a karst landform in the Guizhou Province, China

Three new subaerial species of Achnanthidium are examined and described from a karst landform of central-south China based on light and scanning electron microscopy observations, and are compared with similar taxa worldwide. A. mediolanceolatum sp. nov. is elliptical-lanceolate, not linear-lanceolate as is more typical in this genus, as well as having a bow-tie shaped central area on the raphe valve and a large lanceolate axial area on the rapheless valve, features which together make it easy to distinguish this species from others. A. parvulum sp. nov. and A. guizhouensis sp. nov. are linear-elliptical in shape, which is more common for Achnanthidium and they differ from other species mainly in size, raphe, density of striae and shape of the central area. We compared these three new species with morphologically-similar taxa, and present their ecological settings and distributions as well. The relationship between Achnanthidium and Psammothidium is discussed, and the data from these new species from Guizhou presented herein suggest the two genera are difficult to separate.

<p><strong>Diatom phenotypic plasticity: <em>Olifantiella gorandiana</em> epizoic on ‘G5-Manahere’ (Society Archipelago, South Pacific), a case study</strong></p>

First described from the Mascarenes (Rodrigues Island, Indian Ocean), Olifantiella gorandiana Riaux-Gobin was later observed from several other oceanic basins. We here examine the morphology of this taxon from a scraping of a juvenile green turtle Chelonia mydas Linnaeus, named ‘G5-Manahere’, from Moorea Island (Society Archipelago, South Pacific). In this sample, a great range of morphologies, not previously described for the species, were encountered, demonstrating a high degree of polymorphism with regard to valve shape and also stria pattern. These morphological differences appear to be associated with size, as smaller cells become more rounded. The fine structure (e.g., stria density and pattern) may also be associated with changes in shape. These specimens may all belong to the same and unique taxon: Olifantiella gorandiana. This high degree of polymorphism is described, and put into the context of the constraining epizoic conditions. This study permits furthers the description of the fine structure of O. gorandiana, using focused ion beam (FIB) and scanning electron microscopy (SEM) techniques.

Dwarf-cashew resistance to whitefly (Aleurodicus cocois) linked to morphological and histochemical characteristics of leaves.

The cashew whitefly (CW), Aleurodicus cocois, is an important pest of cashew in Brazil. The use of resistant plants may be an effective strategy for the control of this pest. In a preliminary assay, we found that dwarf-cashew clones show different levels of resistance to CW. Here, we hypothesized that such resistance is associated with morphological characteristics of cashew leaves and their content of phenolic compounds. We determined (i) the attractiveness and suitability for oviposition of five dwarf-cashew clones towards CW, (ii) the leaf morphology and chemistry of those clones, and (iii) the relationship between leaf characteristics and resistance to CW. In greenhouse multiple-choice assays, PRO143/7 and CCP76 showed, respectively, the lowest and highest counts of both CW adults and eggs. Scanning electron microscopy (SEM) analysis revealed that PRO143/7 and EMBRAPA51 have, respectively, the highest and lowest numbers of leaf glandular trichomes. We found a negative correlation between number of trichomes in the abaxial surface of cashew leaves and CW oviposition. In addition, confocal microscopy analysis and histochemical tests with ferrous sulfate indicated a higher accumulation of phenolic compounds in the resistant clone PRO143/7 relative to the other clones. Dwarf-cashew clones did not significantly differ based on the number of leaf epicuticular striations, and the thickness of both leaf lamina and the epidermal layer. The resistance of dwarf-cashew plants to CW is associated with an elevated number of trichomes and accumulation of high levels of phenolics in leaves. Additionally, the contribution of epicuticular striation density and thickness of leaf lamina/epidermal layer are insignificant. © 2019 Society of Chemical Industry.

Polymorphism in Mastogloia (Bacillariophyceae) revisited

Background and aims – Mastogloia grevillei has been shown to be a polymorphic diatom species, producing frustules with morphology of Mastogloia grevillei, frustules with morphology of M. danseyi, and more rarely, heteromorphic or Janus cells with one valve of each morphology.
 Methods – We investigated a wetland population from Iowa (USA) known to produce heteromorphic valves and the type material of Mastogloia grevillei and M. danseyi to clarify the nomenclature of this taxon.
 Key results – The polymorphic shift in stria construction and density between Mastogloia grevillei and M. danseyi occurs in populations sampled decades apart, among widely separated populations, within single genotypes, and independent of sexual reproduction. Combining our observations with observations of type material for Mastogloia grevillei and M. danseyi we propose that Mastogloia danseyi f. grevillei stat. nov. be recognized as an ecophenotype of the nominate Mastogloia danseyi, as the latter taxon has nomenclatural priority. We also provide lectotypes for both taxa.
 Conclusions – Variability in stria structure and density between the two taxa is discontinuous and represents a probable polyphenism for diatoms that is likely triggered by changing total dissolved solids, conductivity, and/or solutes.

Observations of the genus Muelleria (Bacillariophyceae) from the Republic of North Macedonia

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.

Haslea nusantara (Bacillariophyceae), a new blue diatom from the Java Sea, Indonesia: morphology, biometry and molecular characterization

Background and aims – The present study aims to describe a new species of pennate blue diatom from the genus Haslea, H. nusantara sp. nov., collected from Semak Daun Island, the Seribu Archipelago, in Indonesian marine waters.
 Methods – Assessment for species identification was conducted using light microscopy, Scanning Electron Microscopy and molecular techniques. The morphological characteristics of H. nusantara have been described, illustrated and compared to other morphologically similar blue Haslea taxa, distributed worldwide. Additionally, molecular characterization was achieved by sequencing plastidial and mitochondrial genomes.
 Key results – This new species, named Haslea nusantara, cannot be discriminated by its morphology (stria density) but it is characterized by its gene sequences (rbcL chloroplast gene and cox1 mitochondrial gene). Moreover, it differentiates from other blue Haslea species by the presence of a thin central bar, which has been previously reported in non-blue species like H. pseudostrearia. The complete mitochondrion (36,288 basepairs, bp) and plastid (120,448 bp) genomes of H. nusantara were sequenced and the gene arrangements were compared with other diatom genomes. Phylogeny analyses established using rbcL indicated that H. nusantara is included in the blue Haslea cluster and close to a blue Haslea sp. found in Canary Islands (H. silbo sp. ined.).
 Conclusions – All investigations carried out in this study show that H. nusantara is a new blue-pigmented species, which belongs to the blue Haslea clade, with an exceptional geographic distribution in the Southern Hemisphere.

On the identity of Navicula gottlandica (Bacillariophyta), with the description of two new species Navicula eileencoxiana and Navicula bergstromiana from the Australo-Pacific region

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.

Adlafia neoniana (Naviculaceae), a new diatom species from forest streams in Puerto Rico

Background and aims – The samples on which this study is based were collected in two streams in Puerto Rico as part of a long-term monitoring program conducted by the National Ecological Observatory Network (NEON). Detailed study of the diatom assemblages revealed the occurrence of a new diatom species belonging to the genus Adlafia.
 Methods – The study considered 82 samples of epilithic diatoms from two streams in Puerto Rico (Rio Cupeyes and Rio Guilarte) subjected to different degrees of anthropogenic impacts. The new species description is based on high-quality Nomarski (DIC) LM micrographs which document the full spectrum of shape variability along the size diminution series (including girdle views), and SEM images documenting valve ultrastructure (including detailed internal views). In addition we provide information about ecological preferences with respect to trophic state / nutrients, habitat within the stream channel / microhabitat (riffle, run, pool), and season of maximum occurrence.
 Key results – The new species is described as Adlafia neoniana Cantonati sp. nov. It resembles A. drouetiana but has lanceolate (instead of triundulate) outline, slightly-subcapitate to subrostrate ends (instead of subcapitate to capitate), and higher stria density. It is also similar to A. muscora but differs by elliptic-lanceolate (instead of linear-lanceolate) outline, broader valves, and higher stria density. Moreover, the new species was most abundant in an undisturbed, oligotrophic, shaded forest stream whilst A. drouetiana is known from Brazil to be tolerant to organic pollution and eutrophication.
 Conclusions – Adlafia neoniana can be differentiated from other similar species in the light microscope by recognizable characters or character combinations. Its discovery and characterization is a contribution to the knowledge of the still understudied biodiversity of microorganisms in tropical streams.

New Amphora and Halamphora (Bacillariophyta) species from springs in the northern Apennines (Emilia-Romagna, Italy)

Background and aims – The detailed analysis of algae and cyanoprokaryotes in a heterogeneous group of spring habitats (including all the different typologies) of the northern Apennines (Emilia-Romagna Region, Italy) revealed a new Amphora species in a small mountain flowing spring with low conductivity, and a new Halamphora species in a large, inland-saline (Triassic gypsum), fast flowing spring (Poiano spring). The present study aims to describe in detail these two new species found in contrasting spring types.
 Methods – This study is based on light microscopy (both fresh –for plastids – and prepared materials) and scanning electron microscopy observations, as well as a thorough morphological, physical, chemical, and biological characterization of the habitats.
 Key results – Amphora eileencoxiae sp. nov. is most similar to A. vetula (and allied taxa), and is characterized by the outline with acutely rounded, moderately ventrally bent ends, by the dimensions, and by the well-defined, semi-elliptic dorsal area. Halamphora poianensis sp. nov. is most similar to H. gasseae but differs by the higher stria density, the clearly ventrally bent ends, and the strongly developed dorsal raphe ledge.
 Conclusions – This is a contribution to the knowledge of the genera Amphora and Halamphora in mountain springs in understudied geographic areas and inland-saline springs, the species communities of which are likely insufficiently explored.

Cocconeis carinata sp. nov. (Bacillariophyceae) and re-examination of Cocconeis orbicularis Frenguelli & H.A.Orlando and Cocconeis reticulata var. deceptionis Frenguelli & H.A.Orlando

A small and rare (low in abundance) Achnanthales that was first discovered in the Kerguelen Archipelago (Austral Ocean), was subsequently found in the Mascarenes and Scattered Islands (Indian Ocean), and more recently in Nuku Hiva (Marquesas, South Pacific). This marine benthic taxon, first incorrectly identified as Cocconeis reticulata var. deceptionis Frenguelli & H.A.Orlando, is here described as Cocconeis carinata sp. nov. due to its unique features. The scarcity and small size of this diatom render its description difficult under light microscopy, while scanning electron microscopy allows a more detailed description. Cocconeis carinata sp. nov., a sternum valve of which was probably illustrated from the Florida Keys by Montgomery (1978), is a ubiquitous epiphyte and epipsammic taxon. The new taxon has some similarities with Cocconeis nitens Edsbagge, a taxon that is here typified, but with some differences in the stria density on both valves. A re-examination of the historic slides from which C. reticulata var. deceptionis and C. orbicularis Frenguelli & H.A.Orlando were described, leads to the conclusion that the former is a heterotypic synonym of the latter and, due to its complex structure, that C. orbicularis should be transferred to a more suitable genus.

Five new Achnanthidiaceae species (Bacillariophyta) from Jiuzhai Valley, Sichuan Province, Southwestern China

Five new species are described in this study: Achnanthidium jiuzhaienis sp. nov., Achnanthidium epilithica sp. nov., Achnanthidium limosua sp. nov., Achnanthidium subtilissimum sp. nov., and Kolbesia sichuanenis sp. nov. Classification was based on light microscopy (LM) and scanning electron microscopy (SEM). A. jiuzhaienis sp. nov. belongs to the “A. pyrenaicum complex” of the genus Achnanthidium, this classification was based on certain characteristics, such as the possession of transpically-elongated areolae and deflected external distal raphe fissures. A. epilithica sp. nov., A. limosua sp. nov., and A. subtilissimum sp. nov. belong to the “A. minutissimum complex” of the genus Achnanthidium, this classification was based on certain characteristics, such as the possession of straight external distal raphe fissures and round or elliptical areolae. Kolbesia sichuanenis sp. nov. was found to belongs to the Kolbesia genus, based on its elongated areolae and striae comprised of one macroareola. All five species were sufficiently different from other similar species to be considered unique separate species based on their valve outline, shape of the axial and center areas, and density of striae of each taxon. These new species derived from the epilithic and epiphytic collections of four alkaline lakes in Jiuzhai Valley, Sichuan Province, Southwest China.

Three new Fragilaria species (Bacillariophyta) from low-conductivity mountain freshwaters (Alps and Apennines)

More or less needle-shaped species of Fragilaria s.s. are difficult to identify. Here we contribute to the taxonomy of this difficult group by describing three species new to science from very low conductivity mountain freshwater environments. Two of the new species resemble taxa established by Kützing in the early 19th century: F. rumpens and F. vaucheriae. Fragilaria spinaspeciosa sp. nov., from a seepage (helocrenic spring) in the northern Apennines, is superficially similar to F. rumpens, but has a lower stria density. Fragilaria tridentina sp. nov. is distinguished from F. gracilis by its smaller length-to-breadth ratio and more closely spaced areolae. Fragilaria vaucheriaeraetica sp. nov. is distinguished from F. vaucheriae and F. microvaucheriae by its outline and denser striae. These last three species also have distinctly different ecologies. Fragilaria vaucheriaeraetica sp. nov. is found in very low conductivity, very low nitrate, ultra-oligotrophic waters, while F. vaucheriae and F. microvaucheriae are found in medium conductivity, high total phosphorus, and relatively high nitrate streams. Accurate species identification and knowledge of each species’ ecological preferences are critically important if diatoms are to be used effectively as indicators of environmental impact and climate change. Weakly buffered, low alkalinity, low nutrient and low conductivity mountain freshwater habitats are sensitive to human disturbance and biotopes for many rare (Red List) diatoms. As such, they serve as valuable early warning systems for detecting the effects of climate change and other human activities.