We investigated the diatom flora of a wet grassland on mineral soil on the Ritsumeikan University Biwako-Kusatsu Campus (BKC) in Shiga Prefecture, central Japan. The wetland was originally present in the area, but other wetlands that had been present in other parts of the campus were also transplanted there; the wetland has been maintained by pumped-up ground water as well as by the original spring water. A field survey and sampling took place on 8 November 2013. The water was slightly acidic (pH 5.4–6.1) with variable electrical conductivities (4.8–17.5 mS m⁻¹). Diatom samples were collected from the surfaces of Moliniopsis japonica and Sphagnum palusture. In total, 108 diatom species (including nine unidentified ones) belonging to 30 genera were found, and they were all listed and illustrated. In terms of species richness, the dominant genus was Pinnularia represented by 20 species followed by Eunotia with 12 species. While the generic diatom composition was similar to those in peaty moors in Lake Biwa basin, the species composition was much different. We found some diatoms that are unusual in wetlands around Lake Biwa such as Pinnularia osoresanensis, which has been reported only in strongly acidic waters.

Autochthonous diatom flora in Fujimae Tidal Flat, a river-mouth tidal flat in central Honshu, Japan, is displayed as a checklist with microphotographs. We evaluated the diatom flora using the combination of three preparation methods; a nuclear staining method by hematoxylin solution, a sieving method, and a hydrogen peroxide cleaning method. In total 82 diatom taxa were regarded as components of the autochthonous diatom flora. Among them, 52 taxa detected by the nuclear staining method must have been alive on the tidal flat sediments mainly as an epipelon or a sedimented plankton. Sixty eight taxa detected from sieved samples with the relative frequency of >0.5% were putatively living there mainly as an epipsammon.

Diatoms are suspended in the atmosphere as fine particles, but their characteristics such as abundance, species composition, source, moving distance, and the weather conditions required for floating remain uncertain. To assess the amount and species composition of diatoms as fine particles in the lower atmosphere, surveys of fine particles were conducted from 4th to 31st August 2019 and from 8th to 31st January 2020 in Hachirogata reclaimed land, Ogata Village, Akita, Japan. The floating diatoms were usually very sparse, generally were dead, and formed a very minor constituent of suspended particulate matter. The abundance of floating diatoms increased under conditions of low solar radiation, high rainfall, and high wind speed. In such conditions, some living soil diatoms were also observed. The mean length of the diatoms in each atmospheric sample obtained was between 32.2 and 41.5 µm. Considering the size-dependent behavior of particles, diatoms probably underwent long-term suspension and/or repeated short-term suspension in the atmosphere.

A new diatom species, Eupyxidicula atlantica sp. nov., is described from upper Pliocene–lower Pleistocene sediments in the subpolar North Atlantic. Vegetative valves of the new species are domed and have a tubular process with an internal rimoportula, large loculate areolae arranged in a quincunx pattern over the valve, and mantle rimoportulae each with an external simple opening. Resting spore valves have additional rimoportulae scattered over the valve. The tubular process is the most important feature for distinguishing species of the genus Eupyxidicula. In E. atlantica, one (sometimes two) tubular process is found vertically in the valve center and has a hook structure in the middle and a notch at the apex. These characteristic features of the tubular process suggest that the linkage of cell colonies of E. atlantica was weaker than that of other Eupyxidicula species, e.g., E. turris and E. nipponicus, which have many tubular processes on the valve face/mantle area junction. Eupyxidicula atlantica can be differentiated from extant E. turris, E. nipponicus, and E. palmeriana not only by this unique tubular process but also by internal areolar cribra. The cribra of E. atlantica are restricted within hexagonal floors of areolae, whereas those of extant species are continuously distributed from the valve center to the margin. Among fossil species, Stephanopyxis apiculata is similar to E. atlantica in that both species have tubular processes at the valve center. In contrast to E. atlantica, however, S. apiculata has 0–4 tubular processes with no hook and notch structure, and their length depends upon the degree of curvature of valves.

For the purpose of fossil freshwater diatom study, diatoms of the early Miocene Futoro Formation distributed in Setana Town, west coast of Oshima Peninsula, Hokkaido, Japan were investigated. All samples were abundant in centric diatoms (80–92%), but many pennate diatom taxa were also found: 41 taxa of araphid diatoms in addition two taxa of genera and species indeterminable, 14 taxa of monoraphid diatoms and 74 taxa of biraphid diatoms, including some extinct species of all three. One Cocconeis taxon did not match any of the Cocconeis species reported to date. Unable to identify it, we propose it as a new species, Cocconeis setanensis Hidek.Suzuki sp. nov. Also, included herein are nomenclatural transfer for following three pennate taxa, Tetracyclus haradaae (Pantocsek) H.Tanaka, Geissleria longifissa (Hustedt) H.Tanaka and Sellaphora americana f. delicatula (Moisseeva) H.Tanaka, as well as information on 30, unique taxa found in the samples.

A fossil Actinocyclus species is reported from a volcanic ash layer (OT1 Tuff Bed) within middle Miocene marine deposits of the Otogawa Formation, Yatsuo area, Toyama Prefecture, central Japan. The co-occurrence of this species with exclusively freshwater Aulacoseira species suggests a freshwater origin for the Actinocyclus. The freshwater diatoms were present in the water or sediment of a lake on land and were caught up in a pyroclastic flow that was deposited to form the OT1 Tuff bed. The Actinocyclus specimens are neither identified with certainty as a published species nor described as a new species because they have been affected by diagenesis and the valves are poorly preserved; however, the specimens are similar to Actinocyclus krasskei. Their valve morphology is as follows: discoidal; 20–75 µm in diameter; radial or vaguely fasciculated areola rows on valve face; areola density 11–14 in 10 µm; rimoportulae on short hyaline stripes; external pores of rimoportulae are larger than areolae and appear as openings on the mantle just below the valve face/mantle junction; broad fan-shaped rimoportulae expand parallel to the valve face with short stalks that appear as ovals in cross-section; a pseudonodulus is observed under the light microscope on the inside of the valves as a simple pore or a pore with depression; thick silicification with modified areola openings at the external side of the valve face/mantle junction; and large areola chambers with a thin valve wall without spongy structure. These morphological characters resemble those of Actinocyclus krasskei, A. tubulosus, and other non-marine Actinocyclus species. This occurrence of Actinocyclus highlights the importance of volcanic ash for preservation of diatoms in lacustrine settings, and fills a gap in the diatom fossil record of Japan.

This study shows diatom fossil assemblage of the 2011 Tohoku-oki earthquake tsunami deposits and underlying soil in Arahama area, Sendai Plain, Miyagi Prefecture, northeastern Japan. All the major component species with >2% in relative abundance, 27 species belonging to 22 genera, are freshwater species. Surirella angustata and Nitzschia nana are common species in paddy field soil of the inter-ridge marshes, and their abundance in tsunami deposits increases toward inland. This suggests that diatom assemblage in tsunami current became similar as that of soil landward during the tsunami run up the plain. On the other hand, Hantzschia amphioxys and Luticola mutica are abundant in soil on beach ridges. In the tsunami deposits, they showed higher abundance at the sites just behind the beach ridges, and gradually decreased landward. This suggests that they probably transported from beach ridges toward inland due to erosion by the tsunami current. Transport distance of terrestrial diatom fossils is estimated to be a few hundred meters.