An aluminium (or aluminum for my friends over the pond) coated strew slide. No location given, however the label says 210F40 or something like that. The range of species reminds of strews from the Antarctic region. Prepared by John Dale. The aluminium coating has the result of producing a darkground looking image under brightfield lighting conditions. Olympus BHB microscope using 450nm LED light. I chose an Asteromphalus sp. (maybe A. parvulus) for imaging at higher resolution. 63x Leitz Pl Apo 1.4 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, brightfield lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 26 images stacked in Zerene (Pmax).
My ID for this one is tentative. However Asteromphalus parvulus is a pretty good match. Asteromphalus parvulus Karsten 1905. Published in: Karsten, G. (1905). Das Phytoplankton des Antarktischen Meeres nach dem Material der deutschen Tiefsee-Expedition 1898-1899. Wissenschaftliche Ergebnisse der Deutschen Tiefsee-Expedition auf dem Dampfer ‘Valdivia’ 1898-1899 II 2(2): 1-136, pls I-XIX, 1 map, many unnumbered distribution maps. Page 90, Plate 8, Figure 14.
Another good reference: Hallegraeff, G.M., Leblanc, K. New observations on the Antarctic Asteromphalus darwinii/hookeri diatom species-complex (Asterolampraceae). Polar Biol 46, 759–772 (2023). https://doi.org/10.1007/s00300-023-03160-6