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The diatom genus Entomoneis includes species with panduriform frustules characterized by a bilobate, elevated keel, sigmoid raphe canal and numerous open, porous girdle bands. During a phytoplankton survey along the Baltic coast of Sweden, we observed numerous Entomoneis cells, some belonging to the well-known Entomoneis paludosa, while others remained unknown. Morphological and ultrastructural studies of the unknown species were performed with light microscopy (LM), scanning (SEM) and transmission (TEM) electron microscopy, and revealed a unique set of morphological characters. Live cells of Entomoneis grisslehamnensis sp. nov. contain one plate-like plastid and show various degrees of torsion about the apical axis. Microscopic features of cleaned frustules are discussed in comparison with similar species. Most importantly, every 2nd to 5th virga is strongly elevated, uniseriate striae are composed of quadrangular areolae with finely perforated hymenes; the winged keel with a discernible raphe canal is structurally strengthened by raphe fibulae with a flattened wing area, and the main part of the valve bulges towards the margins; striation is decussate on the wings and there is one row of raphe canal areolae at the central area. In addition to describing this new species of an underappreciated, yet cosmopolitan diatom genus, we contribute to the taxonomy of E. paludosa with LM, SEM and TEM details, some of which were not sufficiently noted in original descriptions or re-examination of type material and other specimens made by Dalu et al. [2015. A re-examination of the type material of Entomoneis paludosa (W. Smith) Reimer and its morphology and distribution in African waters. Fottea 15: 11–25] and Long et al. [2022. Ultrastructure of three species of Entomoneis (Bacillariophyta) from Lake Qinghai of China, with reference to the external areola occlusions. PhytoKeys 189: 29–50. doi:]. [ABSTRACT FROM AUTHOR]

In the scientific literature on diatom ecology whether temperature drives changes in diatom assemblage directly or indirectly remains a subject of debate. In order to clarify the relationship between temperature and diatom assemblage composition, we focused on a region with significant seasonal changes but without a freezing period. From March 2016 to March 2018, sediment trap samples were collected monthly to monitor the seasonal succession of diatoms in Douhu Lake, in subtropical southeast China. The results show that in 2016 the variations in abundance of Aulacoseira granulata and Aulacoseira ambigua followed an obvious seasonal pattern, corresponding to the seasonal variation in water and air temperature. In 2016, the thermophilic taxon A. granulata was dominant in the warm season, and in the cold season its abundance declined, while that of A. ambigua, a taxon better adapted to cooler conditions, increased relatively. In 2017, however, there was no such typical seasonal variation. In the cold season of 2017, A. granulata did not decline and there was no significant increase in the cold-preferring A. ambigua. This was related to the large drop in the lake level associated with human activity (substantial water extraction) that occurred during the winter of 2017, which disturbed the natural seasonal fluctuation in water temperature. Thus, in 2017, while air temperature followed the regular seasonal cycle, lake water temperature did not decrease significantly in winter, which allowed A. granulata to maintain a relatively high abundance in the cold season. From these results and an extensive survey of the literature, we conclude that water temperature, more than the seasonal succession, directly drives the fluctuation in abundance of these two Aulacoseira species. [ABSTRACT FROM AUTHOR]

A new freshwater benthic diatom Amphora baotuensis is described from a karst spring in China, based on morphological and molecular phylogenetic data. Based on SSU rRNA and rbcL sequences the molecular phylogeny indicates that this species is closely related to A. copulata (Kützing) Schoeman & Archibald within the Amphora sensu stricto clade. Amphora baotuensis differs from congeners by a combination of morphological features including smaller cell size, a wide, rectangular to fan-shaped dorsal fascia, a well-developed raphe ledge on the ventral side and uniseriate ventral striae. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Three new species of Hannaea Patrick from the Hengduan Mountains in China are formally described herein, based on light and scanning electron microscope observations. Hannaea yalaensis sp. nov. has three continuous inflations along the ventral margin, resulting in an undulate outline compared to the outline of the most commonly reported Hannaea species. The valve of Hannaea hengduanensis sp. nov. is narrower, asymmetrical about the apical axis with capitate apices, dorsal and ventral sides almost parallel. On the ventral side of valve is an unornamented central area. The valve of Hannaea clavata sp. nov. is clavate. Valve margin is straight or slightly curved. The apices of the valve constrict sharply to form the capitate ends. In addition, we also briefly described other Hannaea from this region. Here, we document the morphologies of these new species and discuss the biogeographic distribution of the genus Hannaea in Asia. [ABSTRACT FROM AUTHOR]

Two new species of Cymbella, Cymbella stigmacentralis sp. nov. and C. compactiformis sp. nov., are described. Both C. stigmacentralis and C. compactiformis have a wide size range, with distinctive valve outlines that change markedly from the largest to the smallest. They also occasionally show one or two stigmoid-like pores on their dorsal (secondary) side. Cymbella stigmacentralis and C. compactiformis share features of the apical pore field: a complete area which is not divided by the distal raphe fissure; round foramina arranged in parallel; each pervalvar row of foramina covered internally by an undulate flap-like silica strip. Based on the characteristics of these two new species that lack a constant valve outline, and their fine morphological structures, it is worth studying species of Cymbella more intensively. [ABSTRACT FROM AUTHOR]

We present light and scanning electron microscope observations on a new species of the diatom genus Sellaphora, Sellaphora wangii Y.Liu & Kociolek, sp. nov., described from Hainan Island, China. This species has a raised conopeum with an axial groove or trough on either side of the axial area containing striae extending into the trough, and round depressions (i.e. pits) on the valve mantle at both apices. Our new species is distinctive and separated from other Sellaphora taxa by a unique combination of features that includes its valve outline, undulate raphe, and bow-tie shaped hymenes of the internal areola openings. The uncertainty and dynamic nature of the classification of Sellaphora prompted a review of the ultrastructural features found in species assigned to the genus. Based on this review, we identify four distinct groups of Sellaphora taxa organized by different combinations of ultrastructural features: stria structure, external and internal openings of the areolae, conopeum, polar bars, and apical pits. Based on the features present in our new species, it would be placed in the group that includes S. pupula, the generitype. [ABSTRACT FROM AUTHOR]

We present light and scanning electron microscopical observations on frustules of a new species of Clipeoparvus Woodbridge et al. from Tibet. Cells are small, lens-shaped to conical, have internally occluded areolae and lack any processes. The Tibetan species differs from Clipeoparvus anatolicus Woodbridge, E.J. Cox & Roberts, the only other known species of the genus described from Turkey, by the number, size and structure of the spines on the valve face. Two morphs were encountered, one bearing spines and the other without spines, and they can occur separately or in the same frustule. This phenomenon may be an example of Janus cells within this taxon. The biogeographic distribution of this taxon is discussed. [ABSTRACT FROM AUTHOR]

Three needle-shaped Ulnaria species are studied using light and scanning electron microscopy. One is identified as Ulnaria acus (Kützing) Aboal and two are proposed as new: Ulnaria rhombus sp. nov. and Ulnaria wulingensis sp. nov. These three species have many common characters: needle-shaped valve outline, ghost striae, a central area circumscribed by shortened striae composed of one or a few areolae, a closing plate composed of a solid plate with some struts connecting the areola wall, and characteristic virgae-vimines structure. Ulnaria acus and U. wulingensis have almost parallel central area margins whereas U. rhombus never has parallel central area margins. Ulnaria wulingensis and U. rhombus (excluding few very small specimens) possess distinctive parallel distal regions of variable length, between 3 and 40 µm, but U. acus only has parallel distal regions in a few, very long specimens. Comparison with similar Ulnaria taxa was carried out and the distinguishing characteristics are summarized. All three species were found in alkaline freshwater (pH 8.3–8.5) with low-moderate conductivity (109.2–286.4 µS/cm). [ABSTRACT FROM AUTHOR]

A new araphid diatom,Diatoma kalakulensissp. nov., was discovered in Lake Kalakul, located in the Pamir Mountains in north-western China. The morphology and ultrastructure of this new species are described on the basis of observations made under light and electron microscopy. Compared toDiatoma tenuis,Diatoma kalakulensisis characterized by longer valves, higher stria density, wider apical ends and the position of its rimoportula. [ABSTRACT FROM AUTHOR]

A five-year (January 2009–December 2013) monthly monitoring program was undertaken in Shahe Reservoir to study phytoplankton dynamics and their relation to several key controlling factors including nutrient content and temperature. The results revealed that the phytoplankton biomass showed a significant single peak (mean of 30 mg/L) during May–July. The predominant genera showed significant seasonal succession, with the peak value of diatom biomass appearing in late spring and the peak value of cyanobacterial biomass appearing at early summer. Upon reduction of nitrogen and phosphorus, the biomass of phytoplankton in the reservoir decreased drastically. Based on correlation analysis and ordination analysis, biomass of the dominant genera showed significant positive relationships to temperature. The biomass of three dominant genera of Bacillariophyta,Cyclotella,Synedra, andAchnanthes, were significantly and positively related to ammonium concentration, while the biomass of three dominant genera from Cyanophyta,Aphanizomenon,Phormidium, andRaphidiopsis, were significantly and positively correlated to dissolved total P concentration. The results suggested that the phytoplankton biomass in Shahe Reservoir was mainly controlled by climatic factors, such as temperature and precipitation. However, N and P also had a strong influence on biomass and population structure of the phytoplankton as well as on proliferation of blooms. To avoid algal blooms in reservoirs located in southeast China, we suggest that both N and P should be reduced to grade II level of the Chinese surface water standard; more specifically, total N needs to be lower than 0.50 mg/L and total P needs to be lower than 0.025 mg/L. [ABSTRACT FROM AUTHOR]

After the impoundment of Three-Gorges Reservoir, the specific hydrodynamics created sharp nutrient gradients in Xiangxi Bay. To discover how spring blooms in Xiangxi Bay respond to sharp nutrient gradients, we investigated the phytoplankton community composition and dynamics along nutrient gradients and analyzed the strategies of different types of phytoplankton in filling their niches. We observed a total of 148 taxa of 59 genera belonging to seven phyla. Phytoplankton concentration ranged from 0.03 × 107 to 3.74×107 cell L−1 with two pulses during the spring bloom period. Bacillariophyta was the predominant group, which accounted for 75.4% of total abundance. Canonical correlation analysis (CCA) revealed that phytoplankton occurred in optimal niches for their growth across the nutrient gradients. Specifically, species of Bacillariophyta were found in the region with Si:DIN > 1, and species of Cryptophyta, Chrysophyta, Euglenphyta, Pyrrophyta, and some of Chlorophyta were most abundant in the region with DIN:PO4P < 16. High abundances of Cyanophyta and some Chlorophyta were observed in the region where DIN:PO4P > 16. The CCA also indicated a potential nutrient limitation of Si on Bacillariophyta, of DIN on Cyanophyta and some Chlorophyta, and of PO4P on Cryptophyta, Euglenphyta, Pyrrophyta, and some Chlorophyta. Moreover, as a complement for the traditional Redfield ratio of 16N:1P in determining whether N or P limits a system, our study revealed that the stoichiometric ratio of 1Si:1DIN is an important criterion to determine limitation for diatoms. [ABSTRACT FROM AUTHOR]

The population of an unknown naviculoid diatom from Lake Vrana in Croatia was identified as Navicula hedinii, a species described in 1922 from a small lake in eastern Turkestan (China). This species has some similarities with Navicula pseudocrassirostris, a marine species found in European coastal waters. Based on the ultrastructure of the two species, they can no longer be included within the taxonomical concept of Navicula sensu stricto. Following a comparative morphological analysis of both species with genera bearing similar characters (Adlafia, Veigaludwigia, Kobayasiella, Cavinula, Stenoneis, Climaconeis, Berkeleya, Sellaphora, Cosmioneis), a new genus, Envekadea is proposed for the two species. The new genus is characterized by a sigmoid raphe course with golfclub-like terminal fissures deflected in opposite directions, the areolae covered by external porous hymenes and the presence of one chloroplast, H-shaped in valve view. [ABSTRACT FROM AUTHOR]