A strew slide from St Laurent, France. Prepared by Bernard Hartley. Mounted in Aroclor and dated April 1975.
A really nice array of diatoms, along with quite a lot of sponge spicules as well. I’ve picked out a few of the more interesting/unusual ones for imaging. Olympus BHB microscope using 450nm LED light. 63x Leitz Pl Apo NA 1.40 objective, oil immersion (other than Aulacodiscus reticulatus which was a 40x Leitz Pl Apo NA 1.00 objective with oil immersion). Olympus Aplanat Achromat condenser, oil immersion, brightfield lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. Imaging stacking done in Zerene (Pmax).
I’ve put a question mark after all of these, as I have yet to find an article which discusses the diatoms present at St Laurent.
Auliscus normanianus ? Fairly sure on the name but this is the first 3 holed Auliscus I have seen. This was the only example on the slide, and unfortunately was underneath a large fragment of another diatom. This can be seen in the images and video footage above. This has lowered the contrast over part of the diatom which is a shame.
Actinoptychus stella ? I had thought this was Actinoptychus gründleri from looking through Schmidt’s Atlas and checking a couple of papers. This one looks similar but not identical to the one in the Atlas. However a diatom expert has mentioned this is probably Actinoptychus stella. Other possible names include Actinoptychus thumii or Actinoptychus stella var. thumii.
Araniscus lewisianus ? Initially I thought this was a circular diatom which was titled, but it does actually look to be oval. A. lewisianus is shown in Schmidt’s Atlas on Plate 66, Figure 12. Not a species I have heard of before, hence the question mark, although it does look similar to the images I’ve now seen. Currently accepted name – Coscinodiscus lewisianus var. lewisianus Greville, 1866. Written about in: Komura, S. (1998). A perplexing morphotype of some centric diatoms inclusive of Coscinodiscus lewisianus Grev. and its allies. Diatom 14: 1-23, 147 figs [photographs], 1 text-fig..
Aulacodiscus reticulatus. A very pretty looking diatom. Unfortunately this one was also overlain by a diatom fragment (at about the 10 o’clock position) and a sponge spicule at the top right which degrades the image in those locations.