An arrangement of 100 forms from the Samoa. Prepared by Watson and Sons Ltd. The mount is on a square glass piece which is then mounted onto another slide. Mountant is yellowed. Olympus BHB microscope using 450nm LED light. I selected a few diatoms for imaging 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. Image stacks prepared in Zerene (Pmax). Lot of question marks with this one….
Cocconeis sp. Underside view. Some stacking artifacts – small low, contrast features. Looking through Schmidt’s Atlas, there were a few possibilities for this C. tenella (Plate 196, Figure 38 and is from Samoa), a form of C. heteroidea (Plate 196, Figure 37) or C. transversa (Plate 196, Figure 39). Given the location, I am veering towards C. tenella, however can’t rule the others out, especially C. heteroidea.
Endictya sp. Looks a bit like E. oceanica, but not sure.
Trigonium formosum var. pentagonale. Ok, a lot going on with names for this. I came across one site where an example like this was referred to as Trigonium graeffeanum. Trigonium graeffeanum, mentioned as being in Schmidt’s Atlas (Plate 79, Figure 1) as Amphitetras graeffeanum, however this image has only 4 points. On the same page is Triceratium formosum var. pentagonalis A.W.F.Schmidt 1882 (Plate 79, Figure 4) which looks to be a very good match for this. Published in: Schmidt, A.[W.F.] (1882). Atlas der Diatomaceen-kunde Series II: Heft 20. pp. pls 77-80. Aschersleben: Ernst Schlegel’s Verlag. This name is currently regarded as a synonym of Trigonium formosum var. pentagonale (A.W.F.Schmidt) Desikachary & Prema. Hence I am thinking this is right. However I also found a document on diatoms from Honolulu which mentioned Trigonium arcticum cf var pentagonalis which could well beTrigonium arcticum var. pentagonale (Tempère & Peragallo) Desikachary & Sreelatha 1989. This looks similar too. So I am leaving this one with a question mark as well.