Three new monospecific genera, H-shaped in girdle view, are described from the early Miocene marine deposits of the Boso Peninsula, central Japan. Tetralophus endocampus gen. et sp. nov., Orthosoma polyporophorum gen. et sp. nov., and Dendrogonia polygoniata gen. et sp. nov. are all bipolar with tall or low elevations and chain-forming by apposition of summit plates or the whole of the valve face is without an ocellus or pseudocellus. Linking spines are present or lacking on the tips of the elevations. The three new genera are placed in the Biddulphiales.
Asteroactina mona gen. et sp. nov. is described as a new Asterolampra-like diatom with an extra rimoportula in a pericentral specialized position, other than those arranged around the valve margin. This rimoportula differs from the others in position, shape and probable function.
Diatoms from Ishite Stream near the Komenono Forest Research Center of Ehime University in Matsuyama, Ehime Prefecture, Japan, were studied. Samples were collected from the surface of pebbles and a cobble on 14 November 2003 and 22 November 2005. Based on light microscopy of cleaned diatom frustules, we identified a total of 99 diatom taxa belonging to 39 genera. A checklist including nine unidentified taxa is provided herein, along with light micrographs. Achnanthes minutissima var. robusta Hust. is raised to species level with its transfer to the genus Achnanthidium, i. e., as Achnanthidium robustum (Hust. ) Ohtsuka comb. nov. et stat. nov. Synedra ramesi Hérib. is transferred to a morphologically more suitable genus, as Ulnaria ramesi (Hérib. ) Ohtsuka comb. nov. Many taxa that have never or rarely been reported from Japanese rivers are noted here. A review of light micrographs in past literature, however, reveals that most of these taxa have in fact been known to occur in Japanese rivers, but have been either unidentified or identified as other taxa heretofore.
The original materials of Cymbella affinis Kütz., Cymbella turgidula Grunow and Cymbella uenoi Skvortsov are examined. I also designate the lectotypes and epitypes using these original materials. The epitype of C. affinis agree with the current concepts of this taxon except for Krammer (2002). The type designations by Krammer for C. affinis and C. turgidula do not have priorities for the designations herein. A new combination, Cymbella uenoi f. nipponica (Skvortsov) comb. et stat. nov., for Cymbella turgidula var. nipponica Skvortsov, is also described.
To investigate the spatial distribution of diatom valves in the surface sediment of Lake Kitaura, and to reveal the factors controlling diatom distribution,60 samples from surface sediments were analyzed. Diatom valve abundance was high (more than 4.0×108 valves g-1) in the area of fine grain sediment distribution, and low (less than 1.0×108 valves g-1) in the littoral zone. Diatom assemblages in the surface sediment were characterized by the predominance of planktonic taxa including Aulacoseira granulata, A. pusilla and Cyclostephanosd ubius. High abundances of tychoplanktonic taxa including Pseudostaurosira spp. (P. brevistriata and other species) and Staurosira spp. (S. construens var. construens, var. binodis, var. exigua, S. venter) were found in shallow areas in the northern and southern parts of the lake, and high abundances of benthic taxa including Navicula spp. and Cocconeis spp. at the northern end and littoral zone of the lake were also recorded. The diatom distributions in the surface sediment of the lake reflect the distribution of planktonic diatoms produced in the overlying lake water, tychoplanktonic diatoms occurred in the shallow area of the lake, and benthic diatoms transported from tributaries and the littoral zone of the lake.
In order to explore the origin and evolution of an endemic diatom species, Stephanodiscus suzukii Tuji & Kociolek, living in Lake Biwa, species and morphological changes of Stephanodiscus spp. for the last 400 ka were elucidated using samples from a 140 m-long core. The first appearance of S. suzukii like-species was approximately 390 ka, close to the timing of the onset of Lake Biwa basin formation. However, their dominance started at about 170 ka. Since their first appearance, changes in dominance from S. sp. D, to S. suzukii can be recognized. During periods of transition, transitional forms of the two species were present in the populations. Morphological changes are apparent in the location of interrupted areolae fascicles, the number of areolae per fascicle and number of fascicles per 10 lam near the margin. The existence of individuals with transitional forms and slow morphological changes during the transition period suggest that S. sp. D, and S. suzukii are identical species. The changes in morphology of S. suzukii are related to shifts in global climates and local crustal movements, suggesting they are survival strategies against severe climate and limnetic changes.
Diatom flora of a Sphgnum bog, Yakumogahara Moor, located in the Hira Mountain Range in west-central Honsyu, Japan, was studied. Eleven samples were collected in May 2004. A total of 50 diatom species belonging to 20 genera were identified and illustrated together with one unidentified species. Frustulia saxonica Rabenh. was the most abundant species and it was dominant in seven of the 11 samples. The predominant genera were Eunotia and Pinnularia, represented by 11 and 10 species, respectively.
112 diatom taxa were identified in sediment cores from Sawano-ike Pond, the water of which is weakly acidic as well as low in electric conductivity. They belong to the following genera: Aulacoseira (8), Brachysira (6), Brevisira (1), Caloneis (2), Chamaepinnularia (1), Craticula (2), Discostella (1), Encyonema (4), Encyonopsis (2), Eunotia (25), Fallacia (1), Fragilaria (2), Frustulia (3), Kobayasiella (2), Luticola (1), Navicula (2), Naviculadicta (1), Neidium (5), Nitzschia (3), Peronia (1), Pinnularia (22), Sellaphora (4), Stauroneis (6), Stenopterobia (2), Surirella (4), Tabellaria (1).
The fine structures of Stephanodiscus excentricus Hust. and S. niagarae Ehrenb. were studied in detail using materials taken from Pleistocene diatomite, Terrebonne, Oregon, USA. The Terrebonne diatomite is the type locality of S. excentricus which is known for the unique characteristic of its valve pattern center which is not located at its geometric valve center. External and internal views of the two Stephanodiscus taxa using SEM and LM photographs show the location and shape of mantle fultoportulae and rimoportulae, as well as fascicles made up of areolae rows.
Aulacoseira distans (Ehrenb. ) Simonsen var. nivalis (W. Sm. ) E. Y. Haw. from Kamanuma (Kama Pond), northern Fukushima Prefecture, Japan is 8.5-17.5 lam in diameter,4-7.5 p. m in height. Striae are arranged straight or slightly spiral,12-16 in 10 [im. Valve face has areolae which are always larger in diameter than those of the mantle. Spines are located on the top of every interstria. Single rimoportula located at the end of one row of areolae, inner shallow ringleist, extending over ringleist. Inner valve face/mantle junction has very thin silica wall.