Planktonic foraminifera, Globigerina sp. and benthic foraminifera, Sorites orbiculus were collected, respectively, at coastal areas and near beaches of Sesoko Island, Okinawa, Japan. From these foraminifera, spheroid endosymbionts without frustules were isolated and cultivated. Since these isolates formed frustules, they were identified as diatoms. The symbiotic diatom from planktonic foraminifera was Amphora leeana sp. nov. From S. or biculus two diatom species, Nitzschia sp. and Nanofrustulum shiloi were recognized.

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A floristic study of marine diatoms ( planktonic and epilithic) in coastal waters Sesoko Isl., Okinawa Prefecture, was carried out. Diatoms were examined using light micr oscopy (LM) and scanning electron microscopy (SEM). A total of 65 taxa (at the species and variety level) were found. Dominant taxa in the samples were Guinardia cylindrus (Cleve)Hasle var. cylindrus, Guinardia striata (Stolterf. ) Hasle, Neocalyptella robusta (G. Norman)Hern. - Becer. et Meave, Proboscia alata (Brightw. ) Sundström var. alata, Bleake leya notata (Grunow) Round and Psammodiscus nitidus (WGreg. ) Round et D. G. Mann were new occurences in Japan.

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Cyclostephanos numataensis sp. nov. i s described from the Numata paleo -lake deposit, inferred to be Upper Pleistocene in origin. The new species is characterized by an interfascicle, which has a rimoportula extending to the valve rim (sometimes a portion or all the interfascicles bearing fultoportulae have these structures positioned near the rim of each interfascicle). Internally, the rimoportula is positioned near the valve rim, and the external opening is on the mid mantle. External tubular extensions of the rimoportula and fultoportulae are lacking, and the ribs on the mantle interfascicles are plain.

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Changes in the periphytic diatom assemblage with improvement in water quality were studied over a 25-year period (1973-1998) of the Katabira River, discharged tap water that had originated from a geographically different system. For the first 10 years, mid-stream assemblages were represented by a few species and dominated by the most tolerant species. Thereafter, the structure of the assemblage changed slightly, and after 1993 the water quality in winter recovered to the same level as that in summer, and the number of species showing a marked increase. During this period, species adapted to clean water conditions -Cocconeis pediculus, Melosira varians, Nitzschia dissipata and Nitzschia fonticolawere added to the newly developing periphytic diatom assemblages.
After 1993, species transported from a different water system via the discharged tap water began to appear at the downstream site from the discharge point of the water purification plant on the Katabira River. In 1997 over a wide area downstream from the discharge point, species that had transported from a different water system were appeared throughout the year. In this area during summer, the transported species, Fragilaria construens f. venter and Skeletonema potamos, were abundant, and during winter when the water temperature was low, Diatoma vulgaris and Gomphonema quadripunctatum, which prefer cool water, appeared. These changes in the periphytic diatom assemblage in the Katabira River reflect the improvement in water quality and the rehabilitation of the physical habitat.

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The grazing effects of a herbivorous fish, Plecoglossus altivelis (ayu), on the species composition of benthic algal communities were investigated in the Kiso River (Nagano prefecture). Algae were collected from the cobbles and boulders with and without grazing scars of ayu. Achnanthidium convergens predominated in the non-grazed algal communities, whereas Homoeothrix janthina in addition to A. convergens in the grazed algal communities. The biomass of H. janthina was greater in the grazed algal communities than in the non-grazed ones. There was no significant difference in the biomass of A. convergens between two kinds of communities. These results indicate that the grazing by ayu affects the algal species composition by increasing the biomass of H. janthina.

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The following five lakes, Hiruga-ko, Kugushi-ko, Suigetu-ko, Suga-ko and Mikata-ko have been collectively called Mikatagoko. The lakes have different salinities, and are located on the coast of Wakasa Bay along the Japan Sea side of Fukui Prefecture, Central Japan.
In this paper we compare the data of Nigorikawa & Nishikata (1975) with the results of our analyses of aquatic conditions and diatom assemblages in 1999 and 2000.
The epiphytic materials and the bottom surface oozes collected from 38 sites in total were used to elucidate the species components of diatom assemblages. In this investigation, the water qualities at the sites were analyzed. Asaresult, we found that the diatom biocoenosis and thanatocoenosis reflected the chemical and physical conditions of the waters.

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Diatoms in an epiphyte algal sample from Sugao-numa (Sugao Swamp) were exam-. ined, and a total of 258 taxa among 39 genera were recorded. All of the taxa that occurred abundantly were attached species in particuler, Eunotia curvata, Achnanthes minutissima, Gomphonema parvulum and Navicula mutica var. mutica. The DAlpo value calculated from the relative frequencies of each taxon observed was 50.7.

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