The fossil diatom resting spore spec i es Periptera tetracornusa sp. nov. is described from Deep Sea Drilling Project Holes 438A and 438B, off Honshu, Japan and the Newport Beach section, California. This species is characterized by four triangular processes on the epivalve. The last occurrence of this species may be dated at ca.10.3 Ma in the early late Miocene. This species may be a useful biostratigraphic marker of the Neogene diatom biostratigraphy of the North Pacific.
Diatom assemblages were collected f r om Lake Ikeda in January 2002, and a total of 141 taxa from 29 genera were recorded. The dominant taxa were Asterionella formosa and Fragilaria crotonensis in the plankton, and Fragilaria construens var. binodis and Cymbella minuta in the sediments.
Two Navicula species are newly described from several Japanese rivers and a pond. Navicula exiloides nov. sp. resembles Navicula exilis, but differs in the size range, apical shape, angle of striation and areola density Although Navicula delicatilineolata nov. sp. bears similarities to Navicula heimansioides, they are distinguishable by the shape of both the valve and axial area.
The ecology of dominant Cyclotella s pp. were studied at four sampling sites during 2000-2001, and eight sampling sites during 2002, in southwestern Taiwan. During the study in 2000-2001, the cell density of Cyclotella was compared with the variation of environmental factors by Pearson correlation analysis. The result showed significant positive correlation with nitrate (r=0.37, p=0.01) and negative correlation with water temperature (r=-0.255, p=0.05). Whereas, other factors such as ammonium, nitrite, orthophosphate, organic phosphate, dissolved oxygen concentration, pH, conductivity and salinity did not reveal any significant correlation. However, the especially high cell density of Cyclotella occurring in 2000-2001 could not be explained solely by nitrate and water temperature. Hence, further study was carried out at eight sampling sites during 2002. The result showed that high cell density correlated significantly with electric conductivity (r= -0.45, p =0.01). It was presumed that electric conductivity was a more important factor reflecting the cell density of Cyclotella. Apart from ecological studies, this paper also investigated the morphology of the dominant Cyclotella spp. and confirmed by using scanning electron microscopy that the local species are mainly Cyclotella meneghiniana Kiitz. mixed with Cyclotella sp.
Two new Pinnularia taxa, Pinnularia acidobionta sp. nov. and Pinnularia kirisimaensis sp. nov., are described. Both taxa are thought to be endemic to Lake Usori, Osorezan, Aomori, Japan and Fudo Pond, Kirishima, Kyusyu, Japan.
We conducted a morphometric study to compare Asterionella specimens from Lake Hovsgol, Mongolia with the neotype specimens of A. formosa Hassan from the Glienicker See, Berlin, Germany. Specimens were digitized and measured for valve length, mid-valve width, head pole width, and foot pole width, and length to mid-valve ratio was calculated. Plots of morphometric measures revealed that specimens from Lake Hovsgol are not in the same size class as those from the Glienicker See. Size change series for each population revealed different rates of size diminution. For Lake Hovsgol specimens valve length change to mid-valve width change had a value of 0.217. For the neotype specimens of A. formosa, valve length change with respect to mid-valve width change was 0.41. A related rate, as a proxy for the relation between size diminution between each lake's population, had a value of 1.25 which indicates that each population vegetatively reproduces at a different rate. Cluster analysis using all morphometric measures resulted in Lake Hovsgol specimens aggregating in a group separate from the neotype A. formosa. With evidence of endemism being more prevalent in diatoms than what was once thought, genetic evidence of possible species differences among Asterionella in other lakes, and different environmental conditions between the two locales of Asterionella in this study, we propose that the Asterionella specimens from Lake Hovsgol are different from the neotypes of A. formosa and should be treated as A. edlundii Stoermer & Pappas sp. nov.
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