Valve Mantle Research Articles

New and Interesting Diatoms from the Shiwan Wetwalls, Yunnan Province, China. III. Valve ultrastructure of four new species of Eunotia (Bacillariophyceae: Eunotiales)

Four new Eunotia (Bacillariophyceae: Eunotiales) species are described from the Shiwan Wetwalls in Yunnan Province, China, based on light and scanning electron microscopy. The four species all share the features that assign them to the genus, including asymmetry about the apical axis, raphe predominantly on the valve mantle, and presence of one or more rimoportulae, and they all possess pseudosepta. They differ from one another in several attributes, however. Three of the species possess striae contained in internal troughs, two have spines (either one stout spine at each apex or blunt spines along the dorsal margin) and one has thickened ridges between the striae. These observations of four new Eunotia species further demonstrates the diversity and uniqueness of this wetwall community in Yunnan.

Lutophila gen. nov., a new diatom genus from the hottest place on Earth, Lut Desert, Iran

The Lut Desert is one of the world’s driest and hottest large deserts. This large basin has shallow groundwater pools that have been studied little for microbial flora, especially diatoms, and the present study is the second attempt. We report a new genus with one new species and the related morphotypes. The genus Lutophila and its type species L. iranica is found in hypersaline pools and a saline river in the Central Lut Desert depression, an area known as the hottest spot in the world. The morphology, systematic position, distribution, and ecological conditions of the new species and its morphotypes are discussed. The new genus Lutophila has a linear-lanceolate, symmetric outline with broadly rounded apices and two kinds of areolae, one on the valve face and one on the valve mantle; these characters resemble those shared by the diatom genera Krasskella, Biremis, Chamaepinnularia and Oestrupia. Lutophila iranica exhibits two morphotypes with similar outline; however, L. iranica morphotype 2 is wider than the L. iranica morphotype 1 and has a more distinctive central area.

A new freshwater gomphonemoid diatom genus from India, with the description of a new species from the Eastern Ghats

ABSTRACT We present light and SEM observations of a new astigmate gomphonemoid diatom from the Eastern Ghats of India. This species, and a closely allied one from the Western Ghats that has a stigma, are similar to other members of the Gomphonemataceae in terms of symmetry and certain valve features. They differ, however, in having groups of differentiated pore fields at both apices. At the headpole, the area bearing the groups of pores is flattened and positioned on the valve mantle, and is not easily seen in light microscopy. For these species we propose the genus Indiconema gen. nov. within the Gomphonemataceae. We evaluate the phylogenetic position of this group and relationships within the family based on valve and girdle band features, which suggest that the new genus is sister to Afrocymbella, a genus apparently endemic to Africa. We compare this basal phylogenetic position with other groups of organisms also found in the Western and Eastern Ghats of India, as well as to fossil taxa in the Gomphonemataceae. The sister taxon relationship with a genus known only from Africa supports a close relationship of the floras of the two regions.

Achnanthidium lucectorii sp. nov. and A. enigmaticum sp. nov., novel diatoms (Bacillariophyta, Achnanthidiaceae) from Texas, U.S.A.

Two new species, Achnanthidium lucectorii sp. nov., belonging to the A. minutissimum complex (species with straight terminal raphe ends), and A. enigmaticum sp. nov., within the A. pyrenaicum complex (species with hooked terminal raphe fissures), are described from Texas, U.S.A. utilizing light and scanning electron microscopy. Achnanthidium lucectorii sp. nov. has a raphe valve with striae located toward the apices composed of polygonal areolae, a marked stauros, a non-expanded raphe fissure, with straight (non-dilated) proximal ends, and distal ends extending onto the valve mantle. Internally, its raphe valve is flat, the proximal ends of the raphe end in small capitate expansions, and the distal ends terminate in low helictoglossae that fuse with the apices by a low apical siliceous thickening. In turn, its sternum valve is unique in that it is mostly flat in inner view, except at the central nodule, which is slightly raised. In turn, A. enigmaticum sp. nov. externally has a raphe valve with raphe distal ends shaped like a closed hook, at these ends the raphe slit surfaces at the valve face/mantle junction; its axial area is raised in external and internal views, with the virgae and striae in a lower position. These and other traditionally considered features are compared in detail with taxa morphologically similar to each of the new species. The significance of these features is discussed based on a literature survey, and the implications of considering the valve surface topography and the external and internal details of the raphe and central area are assessed. The latter, in favor of a continued morphological exploration of Achnanthidium until molecular studies are appropriately integrated into current morphological approaches used in the taxonomy of the genus.

Navicula sinicomeniscus sp. nov. (Bacillariophyta; Naviculaceae), a new species from southwestern China

Based on light and scanning electron microscopy observations, Navicula sinicomeniscus sp. nov. is described here as a new species from oligotrophic Lake Fuxian in Yunnan Province, China. Characteristics of this new species used to assign it to the genus Navicula include filiform, almost straight to slightly curved raphe structure, lineolate striae, and a row of visible, horizontal areolae positioned on the valve mantle at the apices. The key diagnostic features between the new species and other similar species include: valve shape and size, stria and areola densities, as well as the straightness or degree of bending of the raphe. Comparison with morphologically similar species is discussed in detail. These results can help us further understand the morphological and ecological information of the genus Navicula in Fuxian Lake.

The valves morphology of the diatom Coscinodiscus radiatus Ehrenberg (Bacillariophyta) from marine and hypersaline ecosystems

The study of morphology of Coscinodiscus radiatus from the Kara-Bogaz-Gol Bay (the Caspian Sea) revealed that at a salinity of 50 to 262‰ among the investigated characters, valve diameter (variation coefficient CV = 21.2%) was the most variable. The number of areolae on the valve mantle in 10 μm (CV = 9.6%) was the least variable characters. Some quantitative characters (valve diameter and number of areolae on the valve mantle in 10 μm) revealed variability compared to the literature data, based on the study of species from marine waters. An increase in the valve diameter of C. radiatus was noted at a salinity of 60‰, a decrease – at a salinity of 262‰. C. radiatus can be characterize as halophilous capable of tolerate fluctuations in salinity.

Morphology of Coscinodiscus radiatus Ehrenberg (Bacillariophyta) from Kara-Bogaz-Gol Bay (Caspian Sea)

The study of morphology of Coscinodiscus radiatus from Kara-Bogaz-Gol Bay (the Caspian Sea) revealed that among the investigated parameters, the valve diameter was the most variable (variation coefficient CV = 21.2%) at a salinity of 50 to 262‰. The number of areolae in 10 µm on the valve mantle was the least variable characters (CV = 9.6%). The variability of the aforementioned quantitative traits, in comparison with the literature data was revealed. An increase in the valve diameter of C. radiatus at a salinity of 60‰ was noted and a decrease – at a salinity of 216–262‰. Calculation of correlation coefficient between the analyzed morphometric characters revealed a stable positive correlation between the valve diameter and the number of areolae in 10 μm on the valve. Mass development in the Bay conditions allows to characterize C. radiatus not only as a marine euryhaline species occurring in desalinated sea areas, but also as a halophile capable of tolerating wide fluctuations in salinity.

Sellaphora tanghongquii sp. nov. (Bacillariophyta, Sellaphoraceae), a new diatom species from the Southern China

Sellaphora tanghongquii sp. nov. is described from epilithic samples taken from river systems in Southern China. The morphology of the new species is described based on light microscopy (LM) and scanning electron microscopy (SEM), and detailed ecological information is provided. This species has diagnostic features consistent with the genus Sellaphora, including small and linear valves, undulate and filiform raphe, and the presence of internal hymenate occlusions. Compared to morphologically similar species, we found that the new species is the most similar to S. constrictum in valve size and outline, raphe structure, and the external arrangement of the striae. However, S. tanghongquii sp. nov. has the following outstanding features which distinguish from similar species: 1) the valve striae are uniseriate externally and biseriate internally, 2) the shape of areolae are mostly square to elliptical, partly round, oval or irregularly shaped, composed of 2–4 small holes inside externally and round, elliptical, C-shaped, or irregularly shaped internally, 3) undulate valves with a slight constriction near the central portion of the valve, and 4) the presence of a row of separated and small pores on the valve mantle. The species appears to be best assigned to the group of species with axial grooves, which includes the generitype of Sellaphora. The discovery of this new diatom species increases the known biodiversity of the southern regions in China.

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.

Psammothidium elnatanianum sp. nov. (Achnanthidiaceae, Bacillariophyta) a new diatom species found in Holocene sediments (Meghalayan Age) of the Xingu River, Eastern Amazon

ABSTRACT An unknown species of Psammothidium (Achnanthidiaceae) was found in core sediment (~4000 cal yr BP) collected from Xingu ria, located in eastern Amazon Basin (Brazilian Amazon). The detailed morphology of the new species was examined and described using light (LM) and scanning electron (SEM) microscopy. The new species described here is mainly characterized by small valve dimensions, an irregular and expanded central area in rapheless valve (RLV) clearly visible in LM. Under SEM observations, the new species show slightly radiate striae with rectangular to rounded areolae present both on the surface and the valve mantle. Morphology and ecology of the new species is compared to those already described for the genus. Moreover, information about core chronology and the co-occurrence of other diatom species in the sample are also provided.

Rimocostatus bugojnicus gen.et. sp. nov. (Coscinodiscophyceae, Bacillariophyta) – a new fossil diatom genus from Gračanica, Bugojno palaeolake in Bosnia and Herzegovina

A new freshwater fossil diatom taxon Rimocostatus bugojnicus gen. et sp. nov, from Miocene sediments at the Gračanica site, Bugojno palaeolake in Bosnia and Herzegovina, is described. The main morphological feature of the genus is the presence of marginal rimoportulae with simple, round external openings positioned on interfascicles on the valve mantle and stalked, large, wide internal slits, positioned on every costa. Marginal and valve face fultoportulae are absent. With these characteristics, the species shows similarities to both marine and freshwater species, known from recent, and primarily from fossil, diatom deposits. Thus, Rimocostatus bugojnicus gen. et sp. nov. is an important find for understanding the evolution of centric diatom species.

Cocconeis fetscheriana sp. nov. (Bacillariophyta) from streams in California (USA) with reference to the cingulum variability within the placentuloid species complex

A novel diatom species, Cocconeis fetscheriana, is described from streams in California (USA). Detailed light and scanning electron microscopy of its frustules reveal a unique combination of characters. These are a highly variable and often irregular valve outline, rapheless sternum valves with characteristic dumbbell-shaped areolae, forming 7–14 longitudinal rows per hemi-valve, a lanceolate, slightly diagonal sternum separated from the valve apices by up to four areolae, robust closed smooth valvocopula attached to sternum valve mantle by an undulate rim, and raphe valve with distinct submarginal areolae, which always circumradiate the raphe apices. Teratological forms are commonly observed in this novel species and are discussed. Environmental data and morphological comparisons with similar Cocconeis taxa with open valvocopulae are provided. The importance of detailed characterization of the cingulum structure with a particular focus on the rapheless sternum valve valvocopula as diagnostic features in Cocconeis is discussed. Examples of cingulum ultrastructure variability are included from additional undescribed Cocconeis species from another stream in California.

Аulacoseira granulata (Bacillariophyta): двугубые выросты

Characters of rimoportulae are important in the taxonomy of the genus Aulacoseira, but data on the variability of these structures are scarce. We study the rimoportulae number, position and morphology in the centric diatom Aulacoseira granulata from a population оf the Nizhny Tagil Reservoir (Sverdlovsk Region, Russia). A significant variation in the number of rimoportulae on the half of the valve mantle (1–3) and their location (along the entire surface of the valve mantle) is found. Two different types of the rimoportulae on the inner surface of valves within the same species of Aulacoseira are shown. Most often each rimoportula looks like a long spiral tube, less often such tube is short and straight. Externally, each rimoportula opening resembles a funnel-shaped hole which is often accompanied by an oval hole of an unclear function.

New and interesting diatoms from the Shimen Wetwalls, Yunnan Province, China. I. Valve morphology of Melosira radiato-sinuata var. yunnanica Chen (Bacillariophyta: Melosirales) from Yunnan Province, China, with comments on its systematic position

We examine and describe the frustular morphology of the diatom originally described as Melosira radiato-sinuata var. yunnanica from a wet wall in Yunnan Province, China, based on light and scanning electron microscopy. This diatom has carinoportulae present in the central portion of the valve, and prominent caverns present internally around the periphery of the valves. The valve mantle height varies. Based on these features M. radiato-sinuata var. yunnanica is transferred to the genus Orthoseira and recognized as a distinct species. It is compared to other, similar ‘centric’ diatoms. Several other, similar taxa are also formally transferred to the genus Orthoseira, including M. radiato-sinuata, and Melosira undulata var. triocellata. ‘Orthoseira sp. #2' sensu Spaulding and Kociolek is formally described as a new species. A discussion of the morphological diversity within the genus Orthoseira is presented.

Nupela semifasciata (Bacillariophyceae), a new species from subtropical lotic environments in Western Paraná State, Brazil

During a survey on freshwater epilithic diatoms from subtropical lotic environments belonging to the Cascavel River microbasin, ParanĂĄ State, Brazil, we observed populations of a new Nupela Vyverman et Compère species. Morphological and meristic analyses were performed using light and scanning electron microscopy, resulting in the description of Nupela semifasciata sp. nov. This species is characterized by elliptic-lanceolate valves containing subcapitate apices in larger individuals and broadly rostrate-rounded apices in smaller ones, while the length/width ratio gradually decreases as the individuals become smaller. The central area unilaterally reaches the margin and always interrupts the row of areolae on the valve mantle. The valve mantle is externally composed of a second row of areolae near the apices. We cross-checked information with similar Nupela taxa, highlighting the main features that separate them. Nupela semifasciata was found in streams with acidic-neutral pH, low conductivity and low to high nutrient concentrations.

<strong><em>Pseudostaurosira crateri sp. nov.</em> (Fragilariaceae, Bacillariophyta), a new small araphid, fossil diatom species from the Pleistocene (Atlantic Forest, Brazil)</strong>

Pseudostaurosira crateri sp. nov. is described from fossil material analyzed from a Quaternary sediment core retrieved from the Colônia basin (located in the Brazilian Coastal Plain, Atlantic Forest, São Paulo Metropolitan Region). Light and scanning electron microscopy revealed its morphology and enabled its comparison with morphologically similar species from European and African rivers and lakes. The new species features wide and short vimines, a particular characteristic of the genus Pseudostaurosira, in addition to many other exclusive features that distinguish it from any other species in the genus reported to date. Some of these characteristics are: (i) apical pore fields composed of small poroids placed within cavernous troughs carved deep into the valve, (ii) absence of blisters or depositions along the valve mantle edge, (iii) small-sized valve, (iv) presence of incipient or rudimentary spines located on raised virgae at the valve face/mantle junction, and (v) internal accumulations of siliceous material on the volae appearing as concentric discs partially occluding the depression into which the areolae open internally. We further discuss the morphological features of similar species ascribed to the genera Pseudostaurosira, Pseudostaurosiropsis, Staurosirella, Frankophila, and Popovskayella based on literature information. Finally, this study contributes to the knowledge on diatom diversity and its biogeography, especially those from tropical regions, in addition to providing a taxonomical basis for its use as biological markers for paleoenvironmental reconstruction.

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.

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.

Nagumoea hydrophicola sp. nov. (Bacillariophyta), the first diatom species described from sea snakes

Although diatoms colonize a vast diversity of immersed hard-surfaced objects and organisms, many diatom species, and sometimes entire genera, show a clear preference towards a particular type of substratum. Studies of animal-associated diatoms indicate that some epizoic forms may require this specific habitat to thrive, and new diatom taxa are expected to be found on as yet unexplored animal hosts. The current study is the first to investigate the diatom flora of sea snakes. Three museum specimens of yellow-bellied sea snakes (Hydrophis platurus) collected over a period of 23 years from the south-eastern coast of South Africa were examined for their diatom flora. Diatoms were abundant on the sea snakes, but communities were composed of only a few species. A previously undescribed species of Nagumoea contributed over 99% of the total diatom assemblage on both the sea snake skin and sea-snake-associated barnacles (Octolasmis sp.). This diatom dominant is described here as Nagumoea hydrophicola sp. nov., based on detailed observations of its frustule ultrastructure using light and scanning electron microscopy. The species is most similar to N. serrata, sharing a similar valvocopula morphology with two rows of pores. However, it can be distinguished from all currently known congeners by its lanceolate central area, short distal raphe endings not reaching the valve mantle, and doubly perforated abvalvar girdle bands. Environmental preferences of the new species are discussed in the context of its host’s biology.

Fascinorbis gen. nov., a new genus of Stephanodiscaceae (Bacillariophyta) from a Late Miocene lacustrine diatomite

We used light and electron microscopy to characterize a Late Miocene freshwater diatomite deposit in the Chalk Hills Formation, near Payette, Idaho, USA. The diatom assemblage from this sample was nearly monotypic, dominated by a single taxon with similarities to Lindavia bodanica (Thalassiosirales) but with several features uncharacteristic of the genus Lindavia, such as a rimoportula(e) on the valve mantle located on a costa, simple alveolar structure, and spines at the external valve face-mantle junction. A combination of other characters for this species complicate its placement into existing genera, including a lack of central fultoportulae, central area with loculate areolae with domed cribra, and a single ring of mantle fultoportulae with three satellite pores with well-developed cowlings and broad satellite pore covers. Based on this unique set of features, we have established a new genus, Fascinorbis, which appears to represent an important transitional form in the evolution of the Lindavia lineage.