Monoraphid Diatom Research Articles

Cocconeiscrisscrossis sp. nov., a new monoraphid diatom (Bacillariophyta) from southern China.

A novel monoraphid diatom species, Cocconeiscrisscrossis You, Yu, Kociolek & Wang, sp. nov. is examined and described from the Qingyi River and Maolan Nature Reserve of southern China. The morphological description is based on light microscopy and scanning electron microscopy observations and the new species is compared with similar taxa in this genus. The characteristics unique to Cocconeiscrisscrossissp. nov. include its central area extending irregularly to both sides, it having closed valvocopulae with heavily silicified fimbriate margins and poles of the valvocopulae have 'sword-shaped' siliceous extensions. These features differentiate this new species from others in the genus. This new species was found in alkaline waterbodies, including streams, waterfall and ponds. It was usually found as an epiphyte on the stones; however, it was present on other substrates such as mosses.

Planothidiumpseudolinkei sp. nov. (Bacillariophyta), a new marine monoraphid diatom species from the coast of Guangxi, China.

A new marine monoraphid diatom species, Planothidiumpseudolinkei sp. nov., is described from the coast of Guangxi, China. The detailed morphology of this epipsammic diatom is studied by using both light and scanning electron microscopy. P.pseudolinkei differs from congeners by a combination of morphological features including capitate apices, multiseriate striae, a small central area on the raphe valve and an oblong sinus on the rapheless valve. Ecological preferences of Planothidium are also briefly discussed.

Diatoms of the northeastern Gulf of Mexico: Vallithidium (Achnanthales: Achnanthidiaceae), a new monoraphid genus based on Navicula marginulata Cleve

While conducting a systematic investigation of phytoplankton assemblages in the northeastern Gulf of Mexico (GOM) in the aftermath of the Deepwater Horizon blowout we took the opportunity to collect sediment samples from off the coast of Pensacola Bay, Florida. These samples contained sufficient numbers of a monoraphid diatom initially identified as Achnanthes controversa Hustedt (Navicula marginulata Cleve) to examine its fine structure in detail. The results of these investigations clearly show that this taxon could not be accommodated in Achnanthes as currently understood, or in any currently described genus in the Achnanthidiaceae. We, therefore, propose a new genus, Vallithidium, with Vallithidium marginulatum (Cleve), J.A. Nienow & A.K.S.K Prasad as the generitype. Our investigations also show that the taxon Hustedt illustrated from Campeche Bay is not the same as the taxon described from the northeastern Gulf. We therefore describe it as a separate species in the new genus, Vallithidium campechianum sp. nov.

Xenobennettella coralliensis a new monoraphid diatom genus characterized by the alveolate sternum valve with cavum, observed from coral reef habitats.

During a survey of benthic diatoms from the coral reefs of the Indian Ocean (Scattered Islands) and Pacific Ocean (Tuamotu Archipelago), an interesting monoraphid diatom was observed and examined by light microscopy and various electron microscopy methods including Focus Ion Beam milling. Our thorough analysis revealed the similarity of this diatom to Bennettella R.W.Holmes, which we reference in the name: Xenobennettella Witkowski & Riaux-Gobin gen. nov., with Xenobennettella coralliensis Witkowski & Riaux-Gobin sp. nov. as the generitype. The type habitat for this new species is the sublittoral coral reef of Juan de Nova in the Mozambique Channel. The sternum valve of the new genus is characterized by an alveolate ultrastructure with the rim of the alveola opening along the valve margin, resembling the sternum valve of Bennettella. Internally, Xenobennettella differs from the latter by possessing a cavum (horseshoe-shaped chamber) on one side of the valve, in a central axial position. The raphe valve of Xenobennettella has small, marginal, apically elongate chambers, which are internally delineated by transapical ribs that are very similar to Bennettella. However, the raphe in the new genus is different from the latter, resembling some Cocconeis and Planothidium with internal raphe endings bent in the opposite direction, while resembling some Planothidium taxa externally by ending on the apical part of the mantle. This contrasts to Bennettella, which has a unique raphe system, with external raphe endings below the apices, a prominent axial structure and a transapically expanded central area. Likewise, the external surface of Bennettella is different from that of the new genus with a complex mantle structure and biseriate striae. In Xenobennettella, the valve mantle of the raphe valve is simple and perforated by areola. The transapical striae occur in the valve margin and the axial area is ornamented along its course with a single row of densely packed areola on both sides. The characteristics of the raphe valve and alveolate sternum valve place the new genus among the Achnanthidiaceae.

Revision of Monoraphid Diatom Genus Platessa with Description of Platesiberia gen. nov. from Ancient Lake Baikal

A new monoraphid diatom genus, Platesiberia gen. nov., is described based on a detailed morphological investigation using light and scanning electron microscopy. The genus is based upon P. rhombicolanceolata Kulikovskiy & Lange-Bertalot and includes Platessa baicalensis Kulikovskiy & Lange-Bertalot, both species previously described from ancient Lake Baikal. Platesiberia gen. nov. is characterized by having biseriate striae on the raphe valves with uniseriate striae on the rapheless valves. Morphology of striae is helpful to distinguish the genus Platesiberia from Platessa and other monoraphid genera, and we provide a comparison of the new Baikalian genus with other freshwater monoraphid groups.

Planoplatessa gen. nov.-A New, Neglected Monoraphid Diatom Genus with a Cavum.

A new monoraphid diatom genus, Planoplatessa gen. nov., is described on the basis of a detailed morphological investigation using light and scanning electron microscopy. We transferred Achnanthes joursacensis Héribaud, a species described from fossil deposits in France, to our new genus. We investigated material from Mongolia from Recent populations. This taxon is known from fossils to Recent across the Holarctic. Achnanthes joursacensis was previously transferred to the genera Planothidium and Platessa, but the morphology of A. joursacensis does not share all morphological features with these two genera. We discuss important morphological features for the delimitation of monoraphid genera based on careful morphological and molecular investigations we presented previously. Planoplatessa gen. nov. as a genus is characterized by having uniseriate striae on both the raphe and the rapheless valves, a cavum in rapheless valves only, and straight distal raphe ends on the valve face.

Platessa arborea sp. nov. (Bacillariophyceae): A new tree moss dwelling diatom from the Eastern Himalayas, India

Platessa arborea sp. nov. new monoraphid diatom species is described from the tree moss habitat of India’s Sikkim state from the Eastern Himalayan biodiversity hotspot. This new species was described based on light and scanning electron micrographs and compared to morphologically similar taxa. Platessa arborea seems to have an affinity for the aerial habitat and has certain unique morphological features distinct from all the other Platessa species, such as its narrowly rounded apices, wide axial area, and the presence of predominantly uniseriate striae with unusually thick striae density. In India, there have been previous reports of some species from the genera Achnanthes and Cocconeis, which have been eventually transferred to the genus Platessa. However, this is the first formal documentation of the Platessa genus from India.

A new monoraphid diatom species from the genus Karayevia sensu lato (Bacillariophyceae: Stauroneidaceae) with remarks on taxonomy and phylogeny of the genus

A new monoraphid diatom, Karayevia chelonica sp. nov., is described from Nha Trang, Vietnam, isolated from marine littoral habitats. Phylogenetic analysis based on partial 18S rDNA and rbcL sequences places this species within the family Stauroneidaceae, and related to other monoraphid species. Karayevia chelonica sp. nov. differs from other species in the genus in stria density and a broad axial area on the rapheless valve. Morphology and taxonomy of the closely related genera Karayevia, Kolbesia and Madinithidium are discussed. Based on morphological characteristics, we conclude that these three genera might represent a single genus, however, further molecular investigation is required to clarify their taxonomic and systematic affinities.

Achnanthidiumgladius sp. nov. (Bacillariophyceae) - a new monoraphid diatom species from Indonesia.

A new monoraphid diatom species Achnanthidiumgladiussp. nov. is described from Indonesia. The description is based on molecular data (18SV4), morphological analysis and comparison with similar species. According to molecular data, Achnanthidiumgladius sp. nov. is closely related to Achnanthidiumminutissimum. Morphologically, the new species differs from similar species by the absence of a fascia on raphe valve, cell size, and striae density and pattern. The new species is only known from the type locality in Indonesia. Comparison with close related species is given.

Mitochondrial and Plastid Genomes of the Monoraphid Diatom Schizostauron trachyderma

We provide for the first time the complete plastid and mitochondrial genomes of a monoraphid diatom: Schizostauron trachyderma. The mitogenome is 41,957 bp in size and displays two group II introns in the cox1 gene. The 187,029 bp plastid genome features the typical quadripartite architecture of diatom genomes. It contains a group II intron in the petB gene that overlaps the large single-copy and the inverted repeat region. There is also a group IB4 intron encoding a putative LAGLIDADG homing endonuclease in the rnl gene. The multigene phylogenies conducted provide more evidence of the proximity between S. trachyderma and fistula-bearing species of biraphid diatoms.

One new species of Achnanthidium Kützing (Bacillariophyta, Achnanthidiaceae) from the upper Han River, China

The upper Han River plays an important role in the Middle Route of the North to South Water Transfer Project in China. During an investigation of diatom biodiversity in this area, a new benthic monoraphid diatom, Achnanthidium ampliatum sp. nov. was observed from an alkaline tributary. This new species has relatively large valves, with a lanceolate axial area and distal raphe ends curved to the same side on the raphe valve, linear axial area in rapheless valves, with uniseriate striae and round to short slit-like areolae on both valves. We present light and scanning electron microscopic observations to document the new species. A. ampliatum sp. nov. is easily separated from other, similar Achnanthidium and Psammothidum taxa, and we provide comparisons with species that have similar outlines and valve features.

Multigene phylogenetic data place monoraphid diatoms Schizostauron and Astartiella along with other fistula-bearing genera in the Stauroneidaceae1.

Presented here are new insights into the marine monoraphid diatom genera Schizostauron and Astartiella, based on molecular and morphological data, including descriptions of new species. Although no unambiguous morphological synapomorphies between the two genera are currently recognized, they are closely related by DNA sequence data. Heterovalvate frustules of Schizostauron are characterized by a bifid stauros on the raphe-bearing valve and intricate areolate occlusions on the sternum valve. In Astartiella, the raphe-bearing valve is characterized by a process resembling a fistula by morphology, while the sternum valve presents a particular striation pattern. Observations by light and electron microscopy were made, along with a molecular phylogenetic analysis using a three-gene (SSU, rbcL, and psbC) concatenated dataset. Three new Schizostauron species are described (S. kajotkei, S. rawaii, S. papilliareae), and two new combinations proposed (S. citronella and S. trachyderma) for species that were previously included either in Achnanthes and Cocconeis, respectively. Likewise, six new species of Astartiella (A. almalikii, A. bornmanii, A. chunlianlii, A. marksii, A. persica, and A. wangii) are described. Molecular results exclude Schizostauron and Astartiella from three clades of exclusively monoraphid diatoms, the Achnanthaceae, Cocconeidaceae, and Achnanthidiaceae, instead placing them in the Stauroneidaceae. Morphological features of Schizostauron and Astartiella, such as the stauros, fistula, and coaxial internal proximal raphe endings, are found in other genera in this clade, whereas the only common feature with monoraphid diatoms as whole group is the heterovalvy of frustules.

Cocconeis vaiamanuensis sp. nov. (Bacillariophyceae) from Raivavae (South Pacific) and allied taxa: ultrastructural specificities and remarks about the polyphyletic genus Cocconeis Ehrenberg

A small marine monoraphid diatom with a linear-elliptic shape and simple terminal raphe endings was present on Raivavae (South Pacific). Particularly due to its different stria structure on both valves, this taxon is here classified as Cocconeis. The new species was present on the rocky intertidal shore of the coral-reef lagoon, as an epiphyte on a turf. Cocconeis vaiamanuensis sp. nov. can be compared to some other monoraphids with a simple raphe system and a rod-like shape. The new taxon has small marginal processes on the sternum valve (SV) mantle, as previously reported for Cocconeis peltoides. Such processes were also previously observed in Platessa and Psammothidium. A cladistic analysis based on ultrastructure shows an affiliation between several close-by taxa. Cocconeis of the C. peltoides section are close to Psammothidium, whereas other Cocconeis without processes are closer to Platessa and Achnanthidium. A clone of Cocconeis cf. sigillata (SZCZCH1200) allowed for a molecular phylogeny to be reconstructed. The molecular signature of Cocconeis cf. sigillata is close to that of Lemnicola hungarica. Cocconeis is a genus with different and complex morphologies that may be split into independent clades (genera). The SV processes may be a vestigial character reminiscent of an ancestral state.

Achnanthidium tinea sp. nov. – a new monoraphid diatom (Bacillariophyceae) species, described on the basis of molecular and morphological approaches

A new monoraphid diatom species Achnanthidium tinea Tseplik, Kulikovskiy, Kociolek & Maltsev, sp. nov. is described from Indonesia. The species is described on the basis of molecular and morphological analyses. According to molecular data the new species belongs to the clade that includes strains of Achnanthidium minutissimum, Achnanthidium saprophilum and Achnanthidium digitatum. Morphologically, the new species differs quite significantly from other species of the same genus because of linear-elliptic valves with almost parallel sides and strongly radiate striae and a butterfly-shaped fascia on the raphe valve. The morphology and phylogeny of the new species are discussed, and thoughts on the current state of the taxonomy of the genus Achnanthidium are expressed. Our work shows the importance of using molecular data in diatom systematics and also demonstrates the need to investigate rarely studied regions of our planet.

Description of Gomphothidium gen. nov., with light and scanning electron microscopy: A New Freshwater Monoraphid Diatom Genus from Asia

We describe a new genus of monoraphid diatom based on Achnanthidium ovatum T.Watanabe et Tuji in Watanabe et al., a species described originally from Japan. We encountered this species from Yunnan Province in the southwestern part to eastern China, as well as in Luding, Sichuan Province and Xianju, Zhejiang Province, in pristine lotic environments. The species differs from the genus Achnanthidium by being asymmetrical to the transapical axis and has a pseudoseptum at the poles of the interior of the raphe valve which is fused with each helictoglossa. Moreover, a distinct group of condensed striae can be found at the narrower pole ('footpole') of the raphe valve. This appears to be the only known genus of freshwater monoraphid diatoms that is restricted to a single continent.

Planothidium scrobiculatum sp. nov. (Bacillariophyta), a new monoraphid diatom from freshwater Pleistocene deposits of South America

A new monoraphid diatom species appeared successively in paleolimnological records from a Quaternary sediment core (1.5±0.1 Ma) retrieved from ColĂ´nia basin (Brazilian Coastal Plain, Atlantic Forest, São Paulo Metropolitan Region), and is formally described as Planothidium scrobiculatum sp. nov. We studied the new species through light and scanning electron microscopy and discussed its similarity to other members of the genus. The new species has a unique combination of morphological features that allow its separation from all other species in the genus: (1) lanceolate valve outline with cuneate apices, (2) multiseriate striae composed of two to four rows of irregular sized areolae on the rapheless sternum valve (SV), not interrupted at the valve mantle junction, and (3) arrangement of areolae on the valve mantle, grouped in 3 or 4 rows, each composed of 2 to 3 areolae on the SV. Nevertheless, the new species main diagnostic feature is the occurrence of numerous, unusual, small shallow depressions externally located on the SV along the axial area, cavum, and virgae. As a result, P. scrobiculatum is different from similar species under LM and SEM by some evident characters or a combination of characters. This study contributes to the knowledge of the so far understudied biodiversity of microorganisms of tropical regions. In addition, the above-mentioned diversity patterns and the wealth of new diatom taxa inside and around the ColĂ´nia basin (many yet to be described) suggest that further samplings from other localities may provide an insight into its habitat preferences and range, since this area is an exceptional biological entity, worthy of further study.

Majewskaea gen. nov. (Bacillariophyta), a new marine benthic diatom genus from the Adriatic Sea

During a survey of the diatom flora attached to carapaces of loggerhead sea turtles (Caretta caretta) from the Adriatic Sea, a large population of an unknown marine achnanthoid species was observed that could not be assigned to any of the currently described monoraphid diatom genera. Detailed morphological analysis based on scanning electron microscopy observations and comparison with a large number of monoraphid genera such as Madinithidium, Scalariella, Kolbesia and Karayevia, resulted in the description of the new benthic marine genus Majewskaea gen. nov. with the newly described Majewskaea istriaca sp. nov. as generitype. The new genus is characterized by a sternum valve showing a clear recurving ridge surrounding the entire valve margin, the presence of macroareolae closed internally by perforated hymenes, separated by a longitudinal hyaline area, a well-developed sternum and vestigial raphe slits. The raphe valve has a simple straight raphe with bent terminal fissures, a very fine striation pattern composed of macroareolae cut in two by a longitudinal hyaline zone, and a very shallow mantle. The new genus is illustrated using both LM and SEM observations and compared with other resembling marine and brackish Planothidium monoraphid species.

Platebaikalia - a new monoraphid diatom genus from ancient Lake Baikal with comments on the genus Platessa

A new monoraphid diatom genus, Platebaikalia gen. nov., was described based on a detailed morphological investigation using light and scanning electron microscopy. Previously Platessa elegans Kulikovskiy et Lange-Bertalot was described from ancient Lake Baikal, and this species serves as the generitype for the newly-described genus. Platebaikalia elegans is a rare taxon found in the deeper parts of Lake Baikal. Platebaikalia elegans is characterized by having multiseriate striae on the raphe valves with biseriate striae on the rapheless valves, though in some specimens a short third row of areolae may be present in some striae. Morphology of striae is helpful to distinguish the genus Platebaikalia from Platessa and other monoraphid genera. Other morphological features that differentiate our new genus from other monoraphid taxa are discussed. We review the morphological data on Platessa species, and based on these data can recognize eight groups of taxa in the genus. Our analysis shows that Platessa as currently circumscribed may contain groups of species that are quite different from one another morphologically, and possibly includes taxa that could be recognized as different at the genus level. A few new combinations are suggested when taxa from the genus Platessa transferred to genera Psammothidium and Planothidium. Some problems of taxonomy of monoraphid taxa are discussed and we believe that taxonomy of this group of diatoms is in need of special attention in future.

Freshwater Cocconeis species (Bacillariophyceae) from Southeastern Brazil, and description of C. amerieuglypta sp. nov.

ABSTRACTCocconeis Ehrenberg is a monoraphid diatom genus included in the Family Cocconeidaceae. It occurs in marine and freshwater environments, living attached to a substrate by the raphid valve. Through the documentation of the taxa found in LM and SEM analyses, this study aims to increase the knowledge about freshwater Cocconeis species occurring in Brazilian waters. In addition, one new species is formally described here. Seven samples were chosen from a total of 346 samples investigated for monoraphid diatoms in São Paulo state, Brazil, due to their representativeness for Cocconeis biodiversity. These samples include periphytic, metaphytic and surface sediment materials. One sample from Ivory Coast was also analysed to compare a similar taxon with the taxa found. The biodiversity and the occurrence of the genus Cocconeis were low in our study material (nine taxa) despite the great amount of samples analysed for monoraphid taxa. Nevertheless, one taxon was considered a new species, being described here. Finally, this study was based on morphological characters of the frustule observed in LM and SEM analysis, showing the importance of both to better understand the variability of each species and to separate similar taxa.

Cocconeis cascadensis, a new monoraphid diatom from mountain streams in Northern California, USA

A new diatom species, Cocconeis cascadensis, is reported from streams in the Southern Cascade Mountain Range in California (USA). Light and scanning electron microscopy reveals morphological novelties related to the structure of the areolae on the sternum valve, which are surrounded externally by crater-like depressions, as well as apically elongated bumps in the submarginal hyaline area of the raphe valve. The valve morphology of the coarsely striated taxa, Cocconeis placentula var. lineata, C. pseudolineata and C. neodiminuta from the studied streams, and C. disculus from freshwaters in Europe, is presented for comparison. The newly described species possesses a unique combination of morphological features, representing an intermediary between the more complex valve ultrastructure of marine Cocconeis taxa and the freshwater members of the C. placentula species complex, with simple slit-like areolae. Cocconeis cascadensis inhabits cold-water mountain streams with low conductivity, low nutrients and low dissolved organic carbon concentrations.