An arrangement of Ethmodiscus sp. (spelt Ethmoidiscus on the label), from the Java sea, in between two disc diatoms. Recent marine material. More on the name in a minute. Prepared by Eduard Thum. Olympus BHB microscope using 450nm LED light. Given the size of these, the whole arrangement was imaged using a 4x Nikon Plan Apo NA 0.2 objective. Then I imaged one using a 20x Nikon Plan Apo NA 0.65 objective and oblique lighting. Finally to get some better resolution I imaged part of the same one using a 63x Leitz Pl Apo 1.4 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 143 images stacked in Zerene (Pmax).
As for species, I initially thought it might be Ethmodiscus rex, however I don’t think it is now. I think it might be Ethmodiscus gazellae based on Round, F. E. (1980). Forms of the giant diatom Ethmodiscus from the Pacific and Indian Oceans. Phycologia, 19(4), 307–316. https://doi.org/10.2216/i0031-8884-19-4-307.1. Ethmodiscus gazellae (C.Janisch ex Grunow) Hustedt 1928. Published in: Hustedt, F. (1928). Die Kieselalgen Deutschlands, Österreichs und der Schweiz unter Berücksichtigung der übrigen Länder Europas sowie der angrenzenden Meeresgebiete Bd. VII: Teil 1: Liefrung 2. In: Rabenhorst’s Kryptogamenflora von Deutschland, Österreich und der Schweiz. (Anon. Eds), pp. 273-464. Leipzig: Akademische Verlagsgesellschaft m.b.h.. Page 375, Figure 196. Basonym: Coscinodiscus gazellae C.Janisch ex Grunow.
I’d not heard of Ethmodiscus before this one, so it is a new one on me. These are big diatoms but they can get really big – 2-3mm across.