The diatom genus Entomoneis includes species with a unique morphology, having panduriform frustules in girdle view, often twisted about its apical axis, with some unique characters such as a sigmoid raphe on elevated bilobate keel, differently shaped junction lines, numerous girdle bands and variously perforated striae. Most of the species belonging to this genus are found to be brackish or marine, with some occurrences in freshwater habitats, but not one species has been described as exclusively freshwater. In this study, the new freshwater diatom species Entomoneis triundulata sp. nov. is described based on a detailed morphological observation using light and scanning electron microscopy. The specific features of E. triundulata are its triundulate valve margin; the shape of the transition between keel and valve body having a proximal U-shaped end, a slightly curved middle segment and a distal V-shaped end; and five sub-compartments to the frustule cavity. Besides morphological features unique t...

Three new species of Ulnaria from the Wuling Mountains Area, China, have been studied by light and scanning electron microscopy. All possess at least six closed girdle bands. The pattern of valve striation is not uniform as some do not have a corresponding opposite structure. The cells of Ulnaria sinensis sp. nov. are linked and form colonies with frustules connected by interlocking linking spines. U. sinensis has very long valves (296–512 µm) and uniseriate striae. Both Ulnaria ulnabiseriata sp. nov. and Ulnaria gaowangjiensis sp. nov. have biseriate striae. U. ulnabiseriata differs from U. gaowangjiensis in LM by its more lanceolate valve shape as the valves of U. ulnabiseriata taper towards the pole from one third of the length of the valve, whist U. gaowangjiensis tapers towards the pole from two thirds of the length of the valve, and by its larger valve length (105–229 µm vs 61–108 µm). The three new species are all epilithic and were found in freshwater streams in or near nature reserves.

This study deals with Ulnaria species found and described from two regions of China with large climate differences during the period of 2014–2022. The first region, located in the Wuling Mountains and Hunan province, has a subtropical climate and the second in Qinghai, a northwest province of China, has a highland continental climate which is characterized by a cold and long winter and warm, short summer. Previously there were nine new Ulnaria species published from the first region. This study describes 14 additional new Ulnaria taxa, nine of which were found in the first region and five of which were found in the second region. A key to the Ulnaria species that have been described from China is provided. The main morphological characteristics for 63 Ulnaria taxa are summarized in Appendices which allow the division of these Ulnaria taxa into three groups: the seven members of group one all possess both uniseriate striae and valve marginal spines, the 42 members of group two all possess uniseriate or mostly uniseriate striae but without the valve marginal spines, and the 14 members of group three all possess mostly biseriate striae and without valve marginal spines. To summarize the morphological characters of the published Ulnaria taxa and 14 taxa described in this study several conclusions for the characterization of Ulnaria are drawn: 1) each cell has two valve-appressed, long plate-like plastids; 2) living cells of many Ulnaria species often lie in girdle view on a slide because they have deep mantles and some copulae associated with either the epivalve or the hypovalve so that the cell depth is often larger than the valve width; 3) the basic structures forming a valve include sternum, virgae, and vimines/viminules; 4) the valvocopula is a closed hoop which has a similar ultrastructure in all Ulnaria taxa but differs from the other copulae in structure; 5) the configuration of girdle bands is a common condition; 6) the life history of Ulnaria can be divided into the four series of successive stages: auxospore, initial cell, pre-normal vegetative cell, and normal vegetative cell, which is very similar to the life history of Hannaea inaequidentata (Lagerstedt) Genkal and Kharitonov; 7) the closed valvocopula is proposed as a definition character for the genus Ulnaria because demonstrating all girdle bands closed is impracticable.

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).

Three new species of Ulnaria (Kutzing) Compere are described based on light and scanning electric microscopy observations. Ulnaria oxybiseriata D.M. Williams & Bing Liu, sp. nov., has linear-lanceolate to lanceolate valves with apiculate and produced ends, biseriate striae, and a central area mostly forming an incomplete fascia surrounded by shortened striae on one side. Ulnaria jinbianensis S. Blanco & Bing Liu, sp. nov., bears linear-lanceolate valves with rostrate to subrostrate ends in larger valves and cuneate ends in smaller valves, uniseriate stria, and a central area forming a rectangular to trapezoid fascia. Ulnaria dongtingensis Bing Liu, sp. nov., possesses a narrow-lanceolate valve outline with produced rostrate to capitate ends, uniseriate stria, and a central area forming almost square fascia. The valvocopula of all three new species bears the same ultrastructure: 1) a complete valvocopula is a closed ring with the same shape as the valve outline, closely attached to the mantle interior surrounding the valve margin; 2) each valvocopula present a row of poroids which bisects the pars interior and exterior; 3) valvocopula with sawtooth-shaped projections attached to the valve over virgae internally; and 4) the valvocopula closed and hyaline at both apices. All three species were found in alkaline freshwater (around pH 8) with moderate conductivity (c. 102-221 mu S/cm).

Lake Qinghai is an ancient brackish water lake in which several endemic diatom species have been discovered. In this study, a species of Diatoma is observed under light and scanning electron microscopy and described as new, Diatoma sinensissp. nov. The living cells of D. sinensis always lie in girdle view due to the cell depth being much larger than valve width (3.3–8.8 vs. 2.0–3.0 μm). The valves of D. sinensis are characterized by their narrow, linear-lanceolate outline, with capitate to subcapitate apices, the presence of two rimoportulae, one at each apex, embedded in the last rib or located among striae and a 4:2 configuration of girdle bands in normal vegetative cells, with four bands assigned to the epivalve and two to the hypovalve. The new taxon is compared with similar species from the genera Diatoma and Distrionella.