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Volume 31
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  • Tatsuya HAYASHI, Yoshihiro TANIMURA
    Volume 31 (2015) Pages 1-11
    Released: October 06, 2015
    JOURNALS RESTRICTED ACCESS
    A new diatom species, Cyclostephanos ramosus sp. nov., is described from Pleistocene sediments of the Paleo-Kathmandu Lake, Nepal. Cyclostephanos ramosus is a polymorphic species characterized by three morphological variations, which are related to valve silicification, valve size and stratigraphic distribution. Heavily-silicified valves exhibit an annulus and network-like structures in the valve center and narrow secondary costae in the mantle area. Other valves have a variable number of valve face areolae, mantle areolae, costae, and mantle fultoportulae, and show differences in the shape of the mantle costae. The number of costae and mantle fultoportulae also shows variations related to stratigraphic distribution, which occur on a time scale of a few tens of thousands of years. On the basis of morphological characteristic features, C. ramosus is most similar to Cyclostephanos malawiensis, but differs in its domed cribra on the mantle, much deeper mantle and larger distance between spines and mantle fultoportulae. The three morphological variations have different implications. Valves showing variation in silicification reflect an ecomorphological response to available silica, while valves with size-related variations show morphological modification brought about by vegetative cell divisions. The stratigraphic variations are highly suggestive because they indicate that the number and shape of costae, which have been traditionally used to delineate Cyclostephanos species, can vary intraspecifically on long time scales. These facts suggest the careful examination of intraspecific morphological variations on various time scales is required for the taxonomy of Cyclostephanos.
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  • Christopher S. LOBBAN
    Volume 31 (2015) Pages 12-17
    Released: November 26, 2015
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    A new extant species of Grammatophora is distinguished by elaborately areolate valvocopulae. It was collected on blue coral in Apra Harbor, Guam. Valves were narrowly to linear-elliptical, 22–77 µm long by 5–6 µm wide, with transapical striae 19–20 in 10 µm. In these characters valves are very similar to those of G. oceanica and G. marina. The valve is asymmetrical in the apical plane, having a slightly deeper mantle at one end. Valvocopulae were remarkably different from other species in having elongate areolae closed by vela, 11–12 in 10 µm, throughout the valvocopula. Septa were planar, inclined towards the center of the cell. Live cells were not observed but spines on both apices suggest that this species may not form the zigzag colonies typical of common Grammatophora species.
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  • Yasuo KIHARA, Kumiko TSUDA, Chizu ISHII, Erika ISHIZUMI, Taisuke OHTSU ...
    Volume 31 (2015) Pages 18-44
    Released: November 26, 2015
    JOURNALS OPEN ACCESS
    The periphytic diatom flora of Nakaikemi Wetland, a peaty low moor located near the Sea of Japan in Fukui Prefecture, central Japan, was studied. This moor was inscribed as a registered wetland under the Ramsar Convention in 2012. We checked a total of 50 diatom samples collected from the surface of filamentous green algae, living/dead spermatophytes, and mud in the moor in May and November, 2008. The water ranged from slightly acidic to alkaline (pH 5.9–8.8), and electrical conductivity also varied greatly among sites (7–32 mS m-1). In all, 297 taxa belonging to 61 genera are listed and illustrated from these samples, although 36 taxa among them have not been identified to species. In terms of taxa richness, the dominant genus was Pinnularia, represented by 35 taxa, followed by Navicula (24 taxa), Nitzschia and Gomphonema (23 taxa each), and Sellaphora (21 taxa). Several brackish and/or marine diatoms occurred in the samples although the water was fresh. Navicula americana var. moesta Temp. et H.Perag. is raised to species level with its transfer to the genus Sellaphora, as S. moesta (Temp. et H.Perag.) Ohtsuka comb. nov.
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  • Hiroyuki TANAKA, Tamotsu NAGUMO
    Volume 31 (2015) Pages 47-55
    Released: November 26, 2015
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    The Mukaiyama Formation, one of four formations of the Sendai Group located along the Pacific Ocean side of southern Iwate, Miyagi and Fukushima Prefectures, Japan, is a Pliocene fluvial and lagoonal deposits. A sample from black mudstone of the upper Mukaiyama Formation was collected from the upper stream tributary site of Tatsunokuchi Gorge, Sendai City, Miyagi Prefecture. The diatom assemblage of the sample is composed of marine (including brackish) diatoms with a frequency of 52% and freshwater diatoms with a frequency of 48% (Table 1). Among all species, the most abundant was marine species Paralia aff. sulcata (26%), followed by two marine species P. aff. elliptica (9%) and Lancineis fatula (3%). Freshwater species are characterized by many taxa of two genera Pinnularia (16 taxa) and Eunotia (11 taxa). The most abundant species among the freshwater taxa was Eunotia minor (16%), followed by Gomphonema parvulum var. parvulum (5%) and Aulacoseira crassipunctata, Eunotia bidens, E. hexaglyphis, Pinnularia subcapitata var. elongata (all 3%). The assemblage suggests that the sampling site at the Mukaiyama Formation was once a bay or lagoonal environment influenced by freshwater.
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