Recently Paradiadesmis proves as a moderately species-rich subgenus whereas the nominate subgenus of Diadesmis contains, so far known, very few taxa, all similar to the type species, Diadesmis confervacea. Diadesmis fukushimae, Diadesmis tahitiensis, Diadesmis virginiana and Diadesmis paracontenta ssp. magisconcava are proposed as new taxa. Two other probably new taxa, both from French Polynesia, are discussed and shown by SEM or LM and SEM microphotographs respectively. Diadesmis biscutella, known up to now only from New Caledonia (Melanesian Islands), is identified also in two Polynesian islands. The frustules display heterovalvy here facultatively. Diadesmis irata and D. brekkaensis, two commonly misidentified taxa, are shown as distinctly independent species. The holotype of the latter is photographed for the first time and compared with conspecific populations from Central Europe and Central America. Seven other established, but in parts rarely recorded Diadesmis taxa are shown by SEM-photographs for comparison and better identification.
Fragilaria berolinensis and Synedra parasitica have been studied in relation to their current taxonomic position. All the evidence points to a removal to new genera based largely on electron microscopic evidence complemented by their unique habitat requirements, the former planktonic and the latter epiphytic on other diatoms. In addition their ecology and north/south hemisphere occurrence is considered.
The history and nature of Caloneis a re discussed. The genus appears to possess no morphological synapomorphies and cannot be satisfactorily diagnosed versus Pinnularia. Thus, although molecular genetic data could yet show that Caloneis is strictly monophyletic, there is currently no evidence for this view. I suggest that Caloneis has been maintained largely because of historical precedent: diatoms with alveolate striae have been identified tothe level of species or species complex directly, without reference to supposed generic characteristics; only once the species or species complex has been recognized is the diatom assigned to Caloneis, which is done using received knowledge, based on convention.
Epilithic diatoms were collected from a small pond (pH2.3, water temperature 26°C)at Osoresan, Aomori Prefecture, on June 12 1999. The valves of diatoms in this study were examined at 2000 × magnification with light microphotographs. The valve ends were differentiated as rostrate and capitate forms, although significant difference in frequency was not observed. The central part of the valves was severely constricted in 92%, breadth of the axial area was wide in 85%, striae length was disordered in 72%, valve length was 43-73 μm, width at the central part of the valve was 4-8.5 μm, valve width at the widest part of the valve was 6.5-10 μm, and striae density was 10-13 in 10 μm. This taxon is considered new, and is named Pinnularia paralange-bertalotii Fukush., Yoshit. &Ts. Kobay. nov. spec.
The taxonomic history of the diatom genus Asterionella is sketchy at best. At present, delimitation of the genus, and species within it, are unclear. This is presented in a compilation of the taxonomy of Asterionella. In regard to species determination, valve shape variation is important. With the proliferation of splitting diatom taxa at the species level, the need for revision of Asterionella is apparent. We have provided some initial results concerning application of quantitative methods to valve shape variation in Asterionella Seven shape variants may be present in the Great Lakes.
A marine epiphytic diatom Cocconeis convexa Giffen was obtained on seaweeds collected from the tidal zone, and its morphology has been investigated using the light microscopy (LM) and the electron microscopy (EM) with the bleaching method. The valves are elliptic or rhombic. The valve face of the raphid valve (RV) is concave and that of the araphid valve (AV) is complementary and strongly convex. The single plastid is flat and C-shaped. The raphe on the RV is straight, and terminates in slightly deflected belietoglossae internally. The striae consist of small, round areolae and are radiate and uniseriate. The hymenes, with perforations arranged in a centric array, are located near the internal openings of the areolae. On the AV, the striae consist of several alveoli. Each alveolus is occluded by a hymene that has perforations arranged in a parallel array and located near the outer surface. The cingulum of AV consists of three open bands without fimbriae; a valvocopula and two bands with a ligula.
Four new taxa are described: Stelodis cus obscurus n. gen. et n. sp., Heterangion orbiculatum n. gen. et n. sp., Diommatetras grossa n. gen. et n. sp. and Dimeractis vicconstricta n. gen. et n. sp. They are based on specimens from the marine sediment of the Morito Formation, early Miocene in age, distributed in the Miura Peninsula south of Tokyo. Stelodiscus obscurus has discoidal valves thin-walled with highly columnar areolae encased by the hypocaust that allows the valvar wall to be empty to a great extent. The loculate areolae are wholly veiled by a single, homogeneous sheet of extremely fine reticulum. Heterangion orbiculatum is a biddulphioid with circular valves that are bipo lar by a pair of marginal elevations of different sizes, and with poroid areolae aligned in radiating rows with repeated furcations. The elevations project from the valve face, each with an unlamellated ocellus at its summit. Diommatetras grossa is another biddulphioid with quadrate valves that have pseudocellate fields at the rostrate corners and equal-sized elevations paired at opposing corners. Finally, Dimeractis vicconstricta is a panduriform diploneid. The solid axial ster num bears a plicate raphe alongside which are longitudinal canals, one on each side. The canal opens to the frustular cavity through unocculuded pores and to the outside via veiled poroids. Between the sternum and the valvar margin are alveolar chambers that ope n to both sides in bilateral rows, each with a mid-depth occlusion. A taxonomic discussion concludes that the f irst taxon is comparable to Actinocyclus by the marginal ring of fan-shaped rimoportules rising from the porous valvar wall; the second and the third are comparable to the Ceratoneis/Pleurosira complex due to the pericentral rimoportule(s) and the presence of the polar elevations bearing topmost ocelli; and the fouth and final one is separated from Diploneis on the basis of the distinctive canals associated with the dualness of areolar pattern.
Two emergence events in the past 3 800 years have been recognized from the welldated marshy deposits of Lake Sagata. Each emergence event was associated with changes in fossil diatom assemblages. In the mud layers, planktonic Aulacoseira granulata, A. ambigua, and Fragilariaceae dominated, while two peat layers were characterized by aerial and/or aeroterrestrial taxa such as Eunotia praerupta var. bidens and Hantzschia amphioxys. Radiocarbon ages suggest the events had occurred 2100-1700 yr. B. P. and 1700-1300 yr. B. P. Past changes in the balance between precipitation and evaporation might have induced these emergence events.
This study was conducted to clarify the characteristics of periphytic diatom assemblages in a stream rehabilitated with advanced treated sewage, and the changes in periphytic diatom species transported to that stream from a natural stream. A total of 43diatom species were observed in the rehabilitated stream. Among these species, Achnanthes exigua, Fragilaria construens f. venter, Gomphonema parvulum, Nitzschia amphibia and Nitzschia constricta were abundant. Near the discharge point of the sewage effluent the average water temperature was about 21°C (above 15°C even in winter), and the structure of periphytic diatom assemblages had been affected by the high water temperature. Many species adapted to clean water conditions were observed at the sites receiving sewage effluent, suggesting that species transported from other water environments constituted the periphytic diatom assemblage with the species flowing from the sewage treatment plant. The number of species constituting the assemblage in the rehabilitated stre a m increased at site further downstream compared with sites where only sewage effluent was received by species transported from a natural stream to the rehabilitated stream, e. g. Nitzschia dissipata. The abundance of transported species in the periphytic diatom assemblages was less than 10% in many cases. However, it sometimes exceeded 10%, and these species were not observed during the period when water inflow from the natural stream stopped and only a small amount of water was flowing there. The changes observed in transported species at the downstream site in the rehabilitated stream indicate that the seasonal succession of periphytic diatom assemblages is caused by a flow of natural stream water even in a stream where treated sewage is used as maintenance water.
The sampling plots are located on t h e brackish water wetlands, near the Tseng-Wen Estuary, in southwestern Taiwan. It is a wild animal and mangrove conservation area, and many birds feed there. The periphytic algae and water samples were collected seasonally during autumn 1998 to summer 1999 from seven different concentrations of salinity gradient (from 0.6 % to 3.4 % tested in the first sampling season, October 31). In the field, pioneer diatoms growing on the artificial substrates of microscope slides were studied and cultured for a period of 15-days in three seasons; autumn-winter (October to November), winter (January) and spring-summer (March to April). A total of 36 diatom species were observed. The diatoms contributed more than 72 % of the total algal species (50 species). Pennate diatoms were generally the most prevalent, with only three species of centric diatoms found. Microalgal communities were dominated by diatom species except the cyanobacterium of Oscillatoria. After 15 days of culture in the field, there was a significant similarity at the sampling site Twl (0.98** ), Tw3 (0.99**) and Tw4 (0.87**) between the dominant diatoms growing on the artificial substrates and the dominant periphytic diatoms growing on the higher plants or macroalgae in nature, during the autumn-winter season from October 31 to November 14. Moreover, after three seasons, the 15-day of cultures at the nearby corners of Tw1A, Tw1B, TwlC, showed significant similarity between the artificial substrates and natural plant substrates in autumn-winter (mean of 0.99**) and springsummer (mean of 0.91**), but very low similarity during the low winter temperature. Besides, on the artificial substrates of slides, the genera Amphora, Cocconeis, Achnanthes, Melosira and Synedra always were the dominant pioneer diatom assemblages growing on the slides, then, the movable diatom assemblages of the genera Navicula, Nitzschia, Gyrosigma and Pleruosigma moving on the substrates. Finally, as in nature, all of the above genera had opportunities to become one of the co-dominant diatoms, growing on the natural or artificial substrates in these brackish wetland plots.
Diatoms were sampled on 4 February 2001 from two spas, Mine Spa and Katase Spa located in central part of Japan. The salinity at both spas ranged from 0.08% to 0.28% and so they may be termed oligohaline according to Kolbe (1927). The dominant species at station 1 were Pinnularia joculata and Nitzschia frustulum, while N frustulum, Cymbella pusilla, Amphola veneta, N microcephala, Rhopalodia gibberula and P. joculata appeared commonly at station 2 in Mine Spa. One of the dominant species, P. joculata, is regarded as tropical species, since it was originally found in tropical islands and described from a greenhouse in botanical garden in Europe. N. frustulum was dominant in Katase Spa.
Diatom assemblages in the sediment of Lake Yogo were examind, and a total of 180taxa among 30 genera were recorded. Abundant taxa were planktonic, i. e. Aulacoseira granulata, A. ambigua, Stephanodiscus carconensis, Cyclotella stelligera, and Asterionella formosa.