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Valve and band morphology of some freshwater diatoms. V. Variations in the cingulum of Pleurosira laevis (Bacillariophyceae)
Abstract
Frustule ultrastructure of Pleurosira laevis (Ehr.) Compère from an epilithon sample collected from the Missouri River was examined using scanning electron microscopy. Valve characteristics were similar to those found by other authors, whereas certain features of the cingulum were new. The cingulum consists primarily of three girdle bands (a valvocopula and two pleurae). The valvocopula can be complete but open at one end, below the ocellus. However, it is more commonly bisegmented, with two narrow and severable connecting points located in the pars interior region underlapping the mantle. The first and second pleurae are either biligulate or uniligulate and closed, but the former, when uniligulate, may be an open band as well. The second pleura is narrower and more delicate than the first. When a natural cleavage of a band subtends a ligula, the band is prone to break along the cleavage during specimen preparation, thus making difficult the assessment of band form and cingulum arrangement. Regions of band overlap have smooth poreless edges, whereas those of underlap are rimmed with either fine fimbriae or, occasionally, a coarser comblike fringe. The variability of the bands results in a cingulum that can be assembled in at least four different arrangements.
... In P. laevis, the most common freshwater species, two groups of two to four labiate processes are located in unornamented areas lateral to the axis between the ocelli. The valves are finely poroid, and the poroids are arranged in somewhat sinuous rows, and are closed by external cribra (Johnson and Rosowski, 1992). The frustules are elongate in girdle view and live specimens are joined together in zig-zag colonies by secretions of organic material from the ocelli. ...
... The frustules are elongate in girdle view and live specimens are joined together in zig-zag colonies by secretions of organic material from the ocelli. Girdle bands are variable in structure and are ornamented with rows of fine poroids (Johnson and Rosowski, 1992). ...
... The valves have straight or curved striae that extend from the margin to the center. Areolae are closed by external cribra (Johnson and Rosowski, 1992). Girdle bands are variable in structure and are ornamented with rows of fine poroids (Johnson and Rosowski, 1992). ...
... Areolae are closed by external cribra (Johnson and Rosowski, 1992). Girdle bands are variable in structure and are ornamented with rows of fine poroids (Johnson and Rosowski, 1992). ...
The diatoms are a successful group of eukaryotic, photosynthetic microbes that occur in nearly every place there is or has been; that place being water. With over 64,000 named entities, they are one of the most diverse groups of algae. The groups of freshwater diatoms, known as "centric" and "araphid", occur in a wide variety of lotic and lentic systems, and are especially plentiful in plankton communities where they are the favored food source by many primary consumers. This chapter offers light and scanning electron microscope observations on the morphology of the siliceous cell walls of the commonly encountered genera found in the freshwaters of North America. A total of 45 genera are treated (27 centrics and 18 araphids). For each genus we provide original figures, descriptions, and comments on preferred ecological habitats. © 20152015 Elsevier Inc.
... Depending on the species, girdle band formation can occur in different phases during cell cycle, either before or after cytokinesis (Lechner and Becker, 2015). Contrary to valve features, this cingulum has largely been ignored in studies of diatom taxonomy and morphology (Johnson and Rosowski, 1992 (which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. ...
There have been a number of studies that described a serial of type of teratology occurring in different diatom taxa and that highlight the relation between metal concentration and diatom deformities, but this subject still remain not deeply understood. The present study refers to the effect of metal pollution on the diatom Achnanthidium minutissimum s.l. by describing a new form of teratology. The samples were collected in a mine area, Rosia Montana, from Romania. We observed that, exposed to environmental stress, the frustule of diatom cells appeared altered in several ways, with abnormal forms occurring in different diatom species that presented deformed valve outlines, modifications of the raphe canal system, irregular striation or mixed teratologies. In a particular sampling location where A. minutissimum s.l. was identified as the dominant species, 20.53% of the individuals presented an unreported type of deformity. This kind of teratology affects the cingulum, the valvocopula more exactly, by becoming markedly undulate.
... Valves with the same morphology may have a different organization of girdle elements. For example, Johnson & Rosowski (1992) showed 4 variations in valvocopula and pleurae structure and arrangement in Pleurosira laevis. ...
The dogma that diatom cell walls are faithfully reproduced without variation from generation to generation is questioned. We suggest that there are many sources of variation in diatom cell wall morphology, and this polymorphism can be size-dependent and size-free. We discuss three major sources of variation, namely, genetic, ontogenetic and environmental, and present a survey of the literature to support our argument. We also suggest that this variation may be adaptive or circumstantial. It is important for those interested in diatom taxonomy, systematics, and ecology to recognize intraspecific variation in diatom taxa, and the implications variation holds for these disciplines. We call for renewed and robust research programs focused on each of the three major sources of infraspecific variation in diatoms.
... Valves with the same morphology may have a different organization of girdle elements. For example, Johnson & Rosowski (1992) showed 4 variations in valvocopula and pleurae structure and arrangement in Pleurosira laevis. ...
... Pocock and Cox (1982) provided an interpretive drawing of R. arcuatum and identified a "connecting band" in that species as the 1st pleura sensu von Stosch (see Methods: Terminology, below), implying that all the regular girdle bands are copulae. Studies of band morphology in diverse freshwater diatom taxa were carried out by Rosowski et al. (Hoagland and Rosowski 1978, Rosowski 1980, Johnson and Rosowski 1992. Several taxa in the Guam flora, including Rhabdonema cf. ...
Tropical benthic diatoms are poorly known but constitute a rich resource for studies of diatom morphology and phylogeny. A remarkable tabellarioid ribbon-forming diatom with a very distinctive pattern of plastid distribution and unique valve and girdle band characters is described from Guam (Mariana Islands) as a new genus and species, Hanicella moenia. We were able to study the ultrastructure and ontogeny of the girdle bands, to compare several other genera in the Striatellales and the Rhabdonematales with numerous septate copulae and hyaline, non-septate pleurae, and to evaluate their phylogenetic relationships. The last-formed two copulae of M. interrupta have distended septa, the last interlocking with the other via a transverse ridge between two unique “ligules.” The fourth pleura of Hanicella is a delicate, fimbriate band. Views of developing copulae of H. moenia indicated that the septum was formed by ingrowth from the sides rather than from the apex; this blurs the distinction between septate and scalariform valvocopulae. Phylogenetic results (1) confirmed that the Striatellales and Striatellaceae, consisting of Striatella and Pseudostriatella, are unrelated to clades containing Hyalosira, Microtabella, Hanicella, and Rhabdonema; and (2) showed that the Rhabdonemataceae is close to, but separate from, the strongly supported Hanicella/ Microtabella/ Grammatophora clade, for which we propose Grammatophoraceae fam. nov. Formal genus and species descriptions of Hanicella moenia are given and we also propose to restore Hyalosira interrupta to Microtabella F.E. Round with an emended genus description.This article is protected by copyright. All rights reserved.
High-resolution diatom investigation from the Polish ecosystem is presented as a contribution to our knowledge of diatom floristics, ecology, biogeography, and their significance in environmental and climate reconstruction in Poland. The study is based on the analysis of 821 sediment samples taken from different lakes in northern Poland, besides 8 borehole-originated from the Eemian paleolakes sites in central Poland. The preceding diatom results in published papers included the diatom flora that were recorded from different habitats in Poland are mentioned in the present work to complete the Polish diatoms list. The current work is the first part in a series of monographs dealing with the diatom taxa belonging to classes Coscinodiscophyceae, Mediophyceae and subclass Fragilariophycidae. A total of 269 diatom species and varieties belonging to 38 genera are recognized. The checklist is comprising 86 entries of Coscinodiscophyceae that includes all radial centric diatoms and 183 taxa of Fragilariophyceae that includes araphid pennate diatoms. Of these 97 diatom taxa are represented as a new record
for Poland and 12 new combinations and new varieties. A detailed diatom description, distribution in Poland, andautecological information are presented to round up the content of this volume and documented with 120 plates including 2423 excellent light micrographs of diatom taxa, which allows for a better understanding of morphology
to aid in the identification. This work is proposed to contribute towards a general view of the high diatom biodiversity that characterizes Polish ecosystems and provides a revised diatom checklist from Poland. Additionally, it offers the first taxonomic and autecological catalog, which will be significant in the assessment of the water quality monitoring, paleoenvironmental interpretation, and construct the paleoclimate changes.
A new marine benthic diatom, Pleurosira nanjiensis sp. nov., is described from the rocky intertidal zone of the Xiaochaiyu Island of the Nanji Islands in China. Its morphology was examined with light and scanning electron microscopy. Molecular phylogeny was reconstructed based on SSU rRNA and rbcL gene sequences. Pleurosira nanjiensis differs from congeners in possession of a combination of morphological features including the domed valve with broadly lanceolate, elliptical or circular valve outline, two elevated marginal ocelli, two (rarely three) rimportulae, and radiate striae.
This chapter provides an overview of diatom wall construction, morphology (light microscopy [LM]), and structure (electron
microscopy [EM]), cell cytology, and aspects of wall morphogenesis. It also seeks to highlight areas where more information
is required, while stressing the importance of applying descriptive terminology appropriately and consistently.
The worldwide effort to grow nanotechnology, rather than use lithography, focuses on diatoms, single cell eukaryotic algae with ornate silica shells, which can be replaced by oxides and ceramics, or reduced to elemental silicon, to create complex nanostructures with compositions of industrial and electronics importance. Diatoms produce an enormous variety of structures, some of which are microtubule dependent and perhaps sensitive to microgravity. The NASA Single Loop for Cell Culture (SLCC) for culturing and observing microorganisms permits inexpensive, low labor in-space experiments. We propose to send up to the International Space Station diatom cultures of the three diatom species whose genomes are currently being sequenced, plus the giant diatoms of Antarctica (up to 6 mm length for a single cell) and the unique colonial diatom, Bacillaria paradoxa. Bacillaria cells move against each other in partial synchrony, like a sliding deck of cards, by a microfluidics mechanism. Will normal diatoms have aberrant patterns, shapes or motility compared to ground controls? The generation time is typically one day, so that many generations may be examined from one flight. Rapid, directed evolution may be possible running the SLCC as a compustat. The shell shapes and patterns are preserved in hard silica, so that the progress of normal and aberrant morphogenesis may be followed by drying samples on a moving filter paper "diatom tape recorder". With a biodiversity of 100,000 distinct species, diatom nanotechnology may offer a compact and portable nanotechnology toolkit for space exploration anywhere.
A study of the diatoms Eupodiscus radiatus Bailey and Fryxelliella floridana Prasad, mainly focussing on the mantle and cingulum, provided new morphological information. In E. radiatus dendritic structures and two types of a palisade-like structure fixed to silica rings were found on the lower valve mantle. Cingulum presented 1-3 bands with areolae arranged in decussate rows. Furthermore, the pars interior of the valvocopula is fimbriate; and the external openings of the rimoportulae are located along the rim of the scalloped extension. The valvocopula of F. floridana is open and its copula is ligulate. Both bands possess poroid areolae similar in size to the cribral pores on the valve face. The genus Eupodiscus is compared to Fryxelliella, based on material sampled in estuaries of Southern Brazil.
Masses of the chain-forming diatom Biddulphia laevis Ehr. were ob- served in the Maumee River in the summer of 1981. Standing crop of this diatom was de- termined at different thalli portions of its green algal substrate, Cladophora glomerata (L.) Kutz. Ultrastructural observations of valve morphology with SEM indicate this spe- cies is typical of other biddulphioid diatoms, except in the structure of the ocellus-like process, which appears to be intermediate between a typical rimless pseudocellus and the thickened rim of an ocellus. Attachment of B. laevis to Cladophora and the zigzag filamen- tous nature of the chains was observed with SEM and noted to be similar to that of marine centric diatoms of the same type.
The diatom genus Rhoiconeis as originally described by Grunow (1863) contains unrelated and morphologically distinct taxa. Cleve (1894–1895) included the taxa placed in Rhoiconeis in various sections of the genus Navicula. However, a study of type material of two species, Rhoiconeis bolleana and Rhoiconeis garkeana, originally placed in Rhoiconeis has shown that these taxa are not related to Navicula either. It is proposed that the genus Rhoiconeis be re-erected to include Rhoiconeis bolleana and Rhoiconeis (= Navicula) sponsalia and that a new genus, Campylopyxis, be erected to contain Rhoiconeis garkeana. Other taxa originally placed in Rhoiconeis have previously been moved to their appropriate genera. Rhoiconeis and Campylopyxis can be separated primarily by the type of striae and the cingulum.
The possible effect of different salinities on the valve morphology of the marine centric diatom Thalassiosira decipiens was investigated. Cultures were grown in media of salinities ranging from 2 to 35%. for 40 days. Only the 15, 20, 25, and 30%. cultures had sufficient growth for statistical analysis of population differences. Areola shape, pattern, and density changed significantly with decreasing salinity. Valves with areola patterns skewed off-centre were more frequent in the lower salinities. Valve diameter also showed a significant decrease. Valves having reduced or missing fultoportulae and rimoportulae were common in the 15 and 20%. cultures.
The Antarctic marine benthic diatom Entopyla australis var. gigantea (Grev.) Fricke was collected as an epiphyte on red algae at Anvers Island, Antarctica. Cells of E. australis var. gigantea form ribbon-shaped colonies, and the sibling cells are attached by means of mucilage extruded through the apical pore fields of concave valves. No interlocking marginal spines were found in this SEM study. The cingulum is composed of a series of many open bands with elaborations of ligulae (described as rudimentary septa in the literature) at the poles. Each band has a single row of slits at the advalvar margin of the pars interior. The heterovalvate frustule is flexed in girdle view. Valves have simple multiseriate striae arranged alternately on the two sides of the zigzag sternum, but pronounced marginal ridges are seen only in the convex valve. Concave valves have prominent apical pore fields, whereas the convex valves do not. Rimportulae present on both the valves follow the “one per pole” pattern, but differ in structure and orientation of slits on each valve. On the basis of material from Greville's original collection, we designate the lectotype (BM 10265) in this study and confirm our identification of Antarctic specimens. E. australis var. gigantea appears to have continued from the late Oligocene-early Miocene to the present, with its possible centre of distribution on the eastern Pacific coasts.
Rhoicosphenia Grun. is a relatively isolated genus among the biraphid diatoms. Morphological changes in an isopolar member of the genus, Rh. genuflexa (Kütz.) Medlin, were investigated using light and scanning electron microscopy. The fully raphid valve showed changes in its flexure that could be correlated with size reduction during its life history from the initial cells to the smallest cells found in the population. Bands showed changes in number (from three to one) related to size reduction. Rh. genuflexa is morphologically similar to Rh. abbreviata (C. Ag.) Lange-Bert. (=Rh. curvata (Kütz.) Grun.), although the two are distinct taxa. These observations support previous contentions that Rhoicosphenia is a natural taxonomic grouping.
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The interspecific relationships of three euryhaline species of Cyclotella (Bacillariophyta) commonly encountered in large numbers in Choctawhatchee Bay, north-eastern Gulf of Mexico, and their relationships to the other species of the genus, are discussed with particular reference to the origin of euryhalinity in this predominantly freshwater genus. Frustule morphology of Cyclotella choctawhatcheeana sp. nov. is described on the basis of light and scanning electron microscopic observations. The cingulum structure of C. striata (Kutzing) Grunow is also described.
The morphology and fine structure of six species of the monoraphid diatom genus Cocconeis Ehr. have been investigated. The raphid valve is concave and thinner than the convex araphid valve. The vela are located near the internal openings of the areolae in the raphid valve but near the outer surface in the araphid valve. The fine structure of these plates varies very little among the species examined except for the araphid valve of Cocconeis pediculus. The raphe is a simple slit with parallel sides.
The raphe endings in the central area are somewhat dilated on the outer surface but undilated and bent slightly towards the valve margin on the interior.
Each complete cingulum consists of three plain imperforate girdle bands and includes a robust valvocopula. The valvocopulae of the raphid valve frequently bear fimbriae, the morphology of which is distinct for each species.
The central area of the valve is variable in the araphid valve of Cocconeis klamathensis. All taxa show a tendency towards irregularity in the rows of striae on one side of the central area in the raphid valve.
The valve morphology of the brackish-water plankton diatom Skeletonema subsalsum is dependent on salinity. In cells grown at salinities of 3‰ or less, the valve faces were flat and the connecting processes much reduced in length. Cells grown at salinities of 5‰ or higher had dome-shaped valves and extended connecting processes. The effect of an increase in salinity could be duplicated by the addition of sucrose to the growth medium. The growth rate was nearly independent of salinity in the range of 1–10‰. It was concluded that the osmotic pressure of the medium exerts a direct effect on cell-wall morphogenesis in S. subsalsum.
Nitzschia pungens f. multiseries a widely distributed diatom that produces the neurotoxin domoic acid, has adversely affected the mussel (Mytilus edulis) culture industry in eastern Prince Edward Island, Canada. The morphological variations of this phytoplanktonic diatom occurring both in culture and in nature are discussed. Any Nitzschia watch' should include particular attention to the several variations which can be induced by conditions of growth, before deciding on a taxonomic characterization.
Navicula mutica (Kütz.) var. mutica was isolated from the air, cloned on agar, cultured in soil-water bottle, and studied with transmission and scanning electron micros-ropy. The frustules were lanceolate to ovoid with rounded apices, with the apical axis 8.5 ± 3.2 μ and the trans-apical and the transapical axis 3.6 ± 0.6 μm. Striae were composed of two or three puncta, and the mantle bore a single row of puncta aligned with the striae. The ends of the raphe turned away from an isolated punctual in the central area of the valve. The mantle puncta and one or two of the valve-face puncta in each stria opened into a series of transapical grooves in the interior of the valve, the grooves contributing to the appearance of striae in the light microscope. The interior of the mantle also possessed a pair of longitudinal grooves, discontinuous at the apices of the valves. An undulate advalvar margin of the valvocopula likely articulates along the interior longitudinal groove of the mantle. The projections of the undulate margin are perhaps positioned between the transapical grooves and along the longitudinal groove between the dentiform structures formed by the intersection of the double-grooved system. The girdle bands each had two (occasionally three) rows of pores. The pleurae margins were straight and not undulate.
A detailed description of the polymorphism and the fine structure of the frustule of a new diatom, Proteucylindrus taiwanensis gen. et sp. nov., is presented. The valve has 2–4 ocelli and 0–9 labiate processes and the areolae are simple pores. The ocelli do not protrude in the freshwater media but do so distinctly in seawater media with salinities above 5‰. The girdle is composed of several segmented bands. Each band has three segments. The sexual reproduction is by oogamy.
The evolution of the diatoms has never been considered in any detail and this paper sets out some of the problems and discusses briefly the fossil evidence, the likelihood of monophyletic versus polyphyletic origin and the possible habitats of the ancestral forms. We assume that diatoms arose at a fairly early period and certainly long before the Cretaceous, when the first fossil diatoms were deposited. A ‘pre-diatom’ stage is envisaged during which a naked photosynthetic cell acquired a coating of siliceous scales. This was followed by an ‘Ur-diatom’ stage when the siliceous scales differentiated to form valves and girdle bands, to give a recognizable but extremely simple diatom. Evidence for such development is indirect and we discuss this from the standpoint of the structure of scales of modern diatom auxospores, symmetry of initial valves, homology of valves and girdle bands, comparative morphology of auxospore scales/valves/girdle bands and the developmental sequences of modern diatom valve formation. From a discussion of the available data and leaning heavily on electron microscope studies we suggest that there is very considerable evidence to substantiate our hypothesis.
The structure of the frustule of vegetative cells of the diatom Cerataulus laevis Ehrenberg is described in detail. Reported for the first time is a fimbriate edge to the valve mantle. Sufficient morphological differences are noted to justify separation from the genus Biddulphia and the taxon is considered conspecific with Proteucylindrus Li et Chiang. The latter name therefore becomes an absolute synonym.
A detailed description of the fine structure of the frustule and processes of silification of Hydrosera triquetra Wallich is presented. The valve is pseudoloculate with simple pore structure on its inner layer. There are two types of girdle-bands. The valvocopula underlaps the valve mantle and overlaps the copula. Each daughter cell retains two parent girdle-bands and forms two new ones during the cell division.
The valves and girdle bands of Melosira varians C. A. Agardh have been shown to possess greater detail than had been supposed from light microscopy. Spines, pores and projections on the surface of the loculate valve are described, and the precise relationships of the girdle bands to each other and to the valves have been elucidated.
Rhoicosphenia Grun. has been placed by some authors in the monoraphid group with Achnanthes Bory and Cocconeis Ehrenb., and by others near Gomphonema Ehrenb. In order to clarify the systematic position of the genus, the morphology and anatomy of the vegetative cells of Rh. curvata (Kütz.) Grun. were investigated using light and electron microscopy. The structure and formation of the two types of valve are described, and the heterovalvy shown to be of a different type from that of the monoraphids; on the basis of raphe, valve and girdle structure a close relationship between these and Rhoicosphenia is unlikely. Rhoicosphenia shows many resemblances to Gomphonema but the types of pore occlusion present, coupled with apparently slight differences in the mucilage-secreting structures and the girdle, suggest that classification in the same family is unwise. The cryptic asymmetry of the valves, and in particular of the raphe system, is noted and explained with reference to their formation; with respect to this asymmetry two configurations of the valves can occur (named cis and trans types) and the distribution of these in raphid genera is discussed briefly. In view of the lack of evidence in raphid diatoms supporting a classification of bands into copulae and pleurae, it is recommended that this practice be suspended.
Thalassiosira bulbosa Syvertsen is described from one clonal culture and natural marine, arctic material collected from brown spots on the ice and from seawater close to the ice border. The new taxon belongs to the group of Thalassiosira species with a single central strutted process and one marginal ring of strutted processes. Specific features are the conspicuous bulbshaped outer part of the marginal strutted processes and a strutted tube surrounded by two oblong, bean-shaped satellite pores. T. bulbosa forms resting cells differing from the vegetative cells mainly in the degree of silicification and by having fewer openings through the frustule. The species may obtain its maximal cell size by a purely vegetative auxospore formation.
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The diatom genus Cylindrotheca Rabenhorst (with a reconsideration of Nitzschia closterium)
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