A strew slide from River Colne oysters. Wide range of species present. Prepared by William Gatrell. Olympus BHB microscope using 450nm LED light. As well as the strew, I imaged a couple with 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. Images stacked in Zerene (Pmax).
As for ID’s, one I think is Gyrosigma fasciola, and the other may be Gyrosigma distortum although I am less convinced about the second one.
Gyrosigma fasciola (Ehrenberg) J.W.Griffith & Henfrey 1856. Published in: Griffith, J.W. & Henfrey, A. (1855). The micrographic dictionary: a guide to the examination and investigation of the structure and nature of microscopic objects; illustrated by forty-one plates and eight hundred and sixteen woodcuts. pp. [i]-v, [1]-696, 41 pls. London: John van Voorst. Page 303, Plate 11, Figure 21.
Maybe Gyrosigma distortum (W.Smith) J.W.Griffith & Henfrey 1856. Published in: Griffith, J.W. & Henfrey, A. (1855). The micrographic dictionary: a guide to the examination and investigation of the structure and nature of microscopic objects; illustrated by forty-one plates and eight hundred and sixteen woodcuts. pp. [i]-v, [1]-696, 41 pls. London: John van Voorst. Page 303, Plate 11, Figure 20. Also see Sterrenburg, F. A. S. “Studies on the Genera Gyrosigma and Pleurosigma (Bacillariophyceae).” Proceedings of the Academy of Natural Sciences of Philadelphia, vol. 145, 1994, pp. 217–36. JSTOR, http://www.jstor.org/stable/4064991. Pages 232-233, Figures 29-32.