Aulacodiscus kittonii ‘with 7 rays’. Single example on the slide. 7 processes. Prepared by Watson and Sons Ltd. 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. 97 images stacked in Zerene (Pmax). Interesting ‘flanges’ visible around the outside edges of the processes.
Aulacodiscus kittonii Arnott ex 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 844, Plate 8, Figure 24.
Seems to be a very rare example – 7 (actually 6, 7 or 8) processes were not observed in the paper by Robert W. Holmes & Albert Mahood (1980), Aulacodiscus kittonii Arnott – distribution and morphology on the West Coast of the United States, British Phycological Journal, 15:4, 377-389, DOI: 10.1080/00071618000650381).
For an example with 8 processes see here.