A nicely made slide, but I am fairly sure the name is wrong. This is (I think) Actinoptychus decorans, not Actinoptychus stella. More on this later. Single example in between two other diatoms. From Cormacks (presumably Cormacks siding), Oamaru, New Zealand. Prepared by T Peters. Olympus BHB microscope using 450nm LED light. 63x Leitz Pl Apo NA 1.40 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, slightly oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 56 images stacked in Zerene (Pmax).
Right, the name. On the slide this is described as A. stella, and with a number after it (132/24). This does not look like A. stella. The number refers to Plate 132, Figure 24 in Schmidt’s Atlas, which does show a diatom which looks like this. Putting the text for Fig. 24 through Google translate gives the following; “Oamaru (Weissfl.) I consider this form to be different from A. Wittianus and do not dare to list it as a var. of the same.”. However Figure 23 on the same plate is A. stella and I think this is where the confusion has come in. On the Oamaru Diatoms website, there are examples of both A. decorans and A. wittianus and to me these look very similar to each other, and to this one. As I have not been able to find other photos of A. wittianus from Oamaru to compare against, I am currently going the name of A. decorans for the one here. A. wittianus is I think also know as A. wittii. All of this just highlights how complex naming these diatoms can be.