An arrangement of six Actinocyclus ralfsii on a slide by Richard Suter. there has been significant movement of what I presume is pigment of the ring around the diatoms, which is especially visible in 4x objective image. Olympus BHB microscope using 450nm LED light. As well as the low magnification images of the arrangement I did a stack of one of them using the 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. 64 images stacked in Zerene (Pmax). This is the lower left one from the 20x objective image.
Actinocyclus ralfsii (W.Smith) Ralfs 1861. Published in: Pritchard, A. (1861). A history of infusoria, including the Desmidiaceae and Diatomaceae, British and foreign. Fourth edition enlarged and revised by J. T. Arlidge, M.B., B.A. Lond.; W. Archer, Esq.; J. Ralfs, M.R.C.S.L.; W. C. Williamson, Esq., F.R.S., and the author. pp. [1]-xii, [1]-968, 40 pls [I-XV]. London: Whittaker and Co.. Page 835. This name is currently regarded as a synonym of Actinocyclus octonarius var. ralfsii (W.Smith) Hendey 1954. Published in: Hendey, N.I. (1954). A preliminary check-list of British marine diatoms. Journal of the Marine Biological Association of the United Kingdom 33: 537-560. Page 557.