An arrangement of three Surirella cardinalis from Connecticut, USA. Prepared by WA Firth. Olympus BHB microscope using 450nmm LED light. As well as the arrangement I imaged the central one at higher resolution. 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. 72 images stacked in Zerene.
The slide says “Transverse striae 68,600 per inch”, so a spacing of 370nm. I measured the spacing on the central one and got a value of 276nm (which would equate to about 92,000 per inch. Of course I am only measuring one area on one example, but it is certainly a ‘fine’ structure.
Also known as Surirella guatimalensis Ehrenberg and Iconella guatimalensis (Ehrenberg) Ruck & Nakov and Surirella davidsonii (for example see here – https://diatoms.org/species/203251/iconella-guatimalensis). The Diatoms of North America link has some good details about it. I can see the 2 spikes at either side of the head pole they mention. Interesting they also say that due to the fine structure it appears ‘structureless under light microscopy’. I can see the striae, but only just and with 450nm light and a 1.4 NA objective. What amazes me is that Firth gave a striae measurement, so presumably he was able to see something with his light microscope as well (in the days before electron microscopy).