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Taxonomic studies on the diatom genus Navicula Bory. Navicula grevillii (C.A.Ag.) Heiberg and N. comoides (Dillwyn) H. & M. Peragallo
Abstract
Two closely related species of the diatom genus Navicula were investigated using light and electron microscopy. A hitherto unrecorded structure associated with the raphe of N. delognei Van Heurck is described.
Examination of type material revealed that the nomenclatural types of N. grevillii (CA.Ag.) Heiberg and N. comoides (Dillwyn) H. & M. Peragallo do not agree with the present understanding of these species, therefore alternative names were sought. All the synonyms of each species were traced and a table of synonymy is supplied. The names N. delognei and N. pseudocomoides are proposed as replacements for N. grevillii and N. comoides respectively and types are cited.
... Navicula, as a genus, according to modern concepts, includes species that were formerly classified in the section "Lineolatae" as defined by P.T. Cleve [12]. This section was raised to a subgenus by Cox [13]. According to the opinion of Round et al. [5], Cox [8,14], and Lange-Bertalot [6], we can describe the genus Navicula as naviculoid diatoms with slit-like raphe with ends curved to secondary valve, and with slit-like areolae (lineolae) in uniseriate striae that lie internally within alveoli or easily between broad and elevated interstriae or virgae (sensu Lange-Bertalot) [6]. ...
A new naviculoid diatom genus, Gandhia gen. nov., was described based on a detailed morphological investigation using light and scanning electron microscopy. Gandhia obtecta (Jüttner and Cox) Kulikovskiy, Glushchenko, Iurmanov, M.Thacker, B.Karthick and Kociolek comb. nov. was previously described as a member of the genus Navicula Bory sensu lato. This species differs from other species in the genus Navicula s.l. by the presence of an internal siliceous lamina covering the alveoli and forming the image of longitudinal lines on either side of the axial area, visible in LM. The presence of this siliceous lamina is similar to laminae in genera such as Pinnularia and Gomphoneis. This unusual morphology is not typical for Navicula sensu stricto, as previously noted by other scientists. Additional investigation of Gandhia obtecta comb. nov. and Gandhia ramosissimoides (H.P. Gandhi) Kulikovskiy, Glushchenko, M.Thacker, B.Karthick and Kociolek comb. nov. from waterbodies of the Western Ghats and the Himalayan region was conducted. Comparison with other species with the same morphological features included two additional species in the genus, namely, Gandhia jakovljevicii (Hustedt) Kulikovskiy, Glushchenko, M.Thacker, B.Karthick, and Kociolek comb. nov. and Gandhia lucida (Pantocsek) Kulikovskiy, Glushchenko, M.Thacker, B.Karthick and Kociolek comb. nov. We discuss the biogeographic patterns of the species, including disjuncts between Europe and Asia.
... Navicula, as a genus, according to modern concepts, includes species that were formerly classified in the section "Lineolatae" as defined by P.T. Cleve [12]. This section was raised to a subgenus by Cox [13]. According to the opinion of Round et al. [5], Cox [8,14], and Lange-Bertalot [6], we can describe the genus Navicula as naviculoid diatoms with slit-like raphe with ends curved to secondary valve, and with slit-like areolae (lineolae) in uniseriate striae that lie internally within alveoli or easily between broad and elevated interstriae or virgae (sensu Lange-Bertalot) [6]. ...
A new naviculoid diatom genus, Gandhia gen. nov., was described based on a detailed morphological investigation using light and scanning electron microscopy. Gandhia obtecta (Jüttner and Cox) Kulikovskiy, Glushchenko, Iurmanov, M.Thacker, B.Karthick and Kociolek comb. nov. was previously described as a member of the genus Navicula Bory sensu lato. This species differs from other species in the genus Navicula s.l. by the presence of an internal siliceous lamina covering the alveoli and forming the image of longitudinal lines on either side of the axial area, visible in LM. The presence of this siliceous lamina is similar to laminae in genera such as Pinnularia and Gomphoneis. This unusual morphology is not typical for Navicula sensu stricto, as previously noted by other scientists. Additional investigation of Gandhia obtecta comb. nov. and Gandhia ramosissimoides (H.P. Gandhi) Kulikovskiy, Glushchenko, M.Thacker, B.Karthick and Kociolek comb. nov. from waterbodies of the Western Ghats and the Himalayan region was conducted. Comparison with other species with the same morphological features included two additional species in the genus, namely, Gandhia jakovljevicii (Hustedt) Kulikovskiy, Glushchenko, M.Thacker, B.Karthick, and Kociolek comb. nov. and Gandhia lucida (Pantocsek) Kulikovskiy, Glushchenko, M.Thacker, B.Karthick and Kociolek comb. nov. We discuss the biogeographic patterns of the species, including disjuncts between Europe and Asia.
Scanning electron microscopy has revealed variation in the ultrastructure of distinctive isolated pores in or near the central area of raphid diatoms, with different types of pores being restricted to phylogenetic groups. Thus, the widespread use of the term stigma for all such pores not only hides the structural diversity but also obscures the phylogenetic distribution of the different types. This paper provides images of the different types of isolated pores, particularly refining the discrimination of variants within the Cymbellales, and reveals some interesting ecological patterns. Revised definitions of stigmata and stigmoids are proposed, together with the recognition and definition of another type of stigmoid. The restricted distribution of more precisely defined pore types shows the importance of consistent use of terminology and its relevance to phylogenetic studies.
The fine structure of a marine tube-dwelling diatom Parlibellas berkeleyi has been examined by light and scanning electron microscopies. The following morphological features of this species are revealed in detail for the first time through the present study. Parlibellns berkeleyi forms a branched colony which consists of several contiguous tubes, and its cells are arranged in a single row in a tube. Parlibellus berkeleyi has the external terminal raphe endings hooked in the same direction, the external coaxial central raphe endings, the internal terminal raphe endings with diminutive helictoglossae, the internal raphe endings slightly turned in the same direction, the central nodule without pores, the areola occluded by the hymen, and the perforated open bands consisted of two types.
We present light and scanning electron microscopy on two new species of Prestauroneis from the Zoigê Wetland, Sichuan Province, China. Prestauroneis nenwai sp. nov. is rhomboid in shape with acutely rounded apices. Striae around the central area are more widely spaced than elsewhere on the valve, and distinct pseudosepta are present. This new species is distinguished from the two previously described species in this genus by the shape and size of the valves. Prestauroneis lowei sp. nov. is more elliptical in outline, with barely protracted, broadly rounded apices. An indistinct pseudoseptum is present at each pole. This second new species is similar to Parlibellus protracta, but differs in outline, especially in the degree to which the headpole is protracted. Some species similar to Prestauroneis have been included in Parlibellus, a genus of quite different morphology. We compare the differences between these two genera, and based on published observations of valve ultrastructure we propose two new combinations, Prestauroneis protractoides (Hustedt) Q. Liu & Kociolek comb. nov. and Prestauroneis protracta (Grunow ex Cleve) Q. Liu & Kociolek comb. nov. Assignment to Prestauroneis of other species in Parlibellus awaits future scanning electron microscopy studies. Although currently a small genus, Prestauroneis may be found across a wide spectrum of environments, from fresh to brackish/marine waters.
This paper describes the results of long-term growth in culture of a clone of Gomphonema parvulum, which demonstrates that this taxon, unlike most other diatoms or other parts of G. parvulum, does not decrease in size as it reproduces vegetatively. After a period of eight months in culture, cells were significantly longer although valve widths were more or less the same. It is suggested that flexibility in the girdle region, particularly at the valve apices allows hypovalves to be the same size as, or longer than their corresponding epivalves. This phenomenon may be more widespread but may not have been noticed because the prevailing paradigm that diatoms decrease in size has not been questioned.
Live and prepared cells of the marine pennate diatom Navicula complanatoides Hust. were examined with light and electron microscopy. It has narrowly lanceolate valves (26–55 μm long, 4–5 μm wide) and girdles 10–24 μm in depth. Striae are parallel at the center of the valve (24–28 in 10 μm), becoming slightly convergent toward the apices.
Electron microscopy revealed that the external valve surface presents a longitudinally ribbed appearance (20–28 parallel ribs at its maximum width), whereas internally, rectangular areolae are occluded by ricae. The raphe slit lies in a narrow axial area, and one side of the raphe sternum is deeper and folds over the other, obscuring the internal opening. Internally, the central virga on one side of the raphe and two virgae on the other are somewhat broader. A conspicuous pore (stigma) is present between the two broadened virgae.
The girdle consists of valvocopulae, copulae, and pleurae. There are 16–20 bands per cingulum. The valvocopulae and copulae are hollow tube-like structures, with inner and outer portions contrsting in morphology. They decrease in diameter in an abvalvar direction. There are four pleurae. These are flat bands which facilitate overlap of the epicingulum and hypocingulum.
Fundamental features of the valve and girdle reveal the distinctness of this species within Navicula. The areolae, external longitudinal ribs, and raphe structure suggest affinities with Pleurosigma, Gyrosigma, and Haslea. It is hypothesized that they share a derived state which indicates a recent common ancestor for these taxa. N. complanatoides and related species of the Naviculae microstigmatacae are distinctive enough to merit their own genus within the Naviculaceae.
Colonies of Berkeleya rutilans (Trent.) Grun., Navicula pseudocomoides Hendey and N. ramosissima (C. A. Ag.) Cleve were examined using light and electron microscopy to elucidate the structure of their mucilage tubes. Each species was found to have a characteristic tube construction which could be used for identification. A summary of features on which these species can be recognized was compiled.
Light and electron microscopic examinations have been made on a number of species previously attributed to the genus Amphipleura Kütz. As a result, two groups of species can be delimited, both of which warrant generic status. The genus Berkeleya Greville is therefore extended to include the marine tube-dwelling species while Amphipleura is confined to the freshwater free-living species. Comparison is made with species of the closely related genus Frustulia C. Ag. and emended generic descriptions are given for Amphipleura and Berkeleya.
The benthic diatom floras at Clevedon and Weston-Super-Mare were studied over a period of two years, with particular emphasis on the tube-dwelling species. Eight sampling sites were regularly visited, the diatom flora at each recorded and comparison made between the sites on each shore and between the two shores. The differences due to seasonal fluctuations in diatom populations, and those due to geographic location are discussed. It is suggested that the type of diatom zonation found during this study is a result of those conditions peculiar to estuaries and may therefore be typical of estuarine diatom zonation in general.
Tube-dwelling diatoms are found in a variety of habitats, from marine to fresh water on different types of substrata; rock, wood, plant and animal. I have described species as tube-dwelling (Cox, 1975 b) if they produce mucilage which is consolidated into a tubular structure around the cells, yet within the mucilage tube individual cells move and divide. The tube is usually attached to the substratum at its base and is extended apically by the secretion of more mucilage by the enclosed diatoms. Tube volume thus increases to accommodate the increased endotubular diatom population. The presence of tube-dwelling diatoms on rocky shores has been recorded by some workers (Aleem, 1949, 1950; Castenholz, 1963, 1967; Hopkins, 1964), while Castenholz (1963, 1967) correlated seasonal and distribution patterns of some littoral species with their response to light intensity and day-length. Carter (1932,1933) described the algal flora, including several tube-dwelling species, of two salt marshes but little work has been done on tube-dwelling diatoms occurring in estuaries. During the course of a study on the biology of these diatoms (Cox, 1975 ft) variation in their distribution at two Severn Estuary sites prompted an investigation into their distribution in the estuary as a whole. Diatom distribution was recorded with reference to the geographical location in the estuary and to the position on the shore at two sites lower down the estuary (Clevedon and Weston-Super-Mare).
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