An Actinoptychus sp. from Palos Verdes, California, USA. Label says ‘A. vulgaris var.’, but I am not sure about that, more in a minute. Mounted in Styrax and dated 30/5/[19]38. Prepared by John J Grover. Olympus BHB microscope using 450nm LED light. 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. 62 images stacked in Zerene (Pmax).
Back to the name. Actinoptychus vulgaris Schumann 1867. Published in: Schumann, J. (1867). Preussische Diatomeen. Schriften der Königlichen Physikalisch-Ökonomischen Gesellschaft zu Königsberg 8: 37-68, 3 pls. Page 64, no figure.
However I am not 100% convinced that is correct for this one. It could be Actinoptychus maculatus (see Päule Hecke’s Oamaru book, Figures 26-29 for A. maculatus compared with Figure 39 for A. vulgaris).
Actinoptychus maculatus A.W.F.Schmidt 1888. Published in: Schmidt, A.[W.F.] (1888). Atlas der Diatomaceen-kunde. Series III: Heft 33-34 [“Heft 29-30”]. pp. pls 129-136. Aschersleben: Verlag von Ludwig Siever. Plate 132, Figures 18–20. Schmidt said this “A. maculatus Gr. &St.. Grunow would like to classify this form as A. splendens or vulgaris. Its validity as a species is guaranteed by the very distinctive form of the processes.”. It also looks like the images for A. maculatus in Schmidt’s Atlas. I will leave it as Actinoptychus sp., with a tentative A. maculatus for now.