Two days ago I found in the plankton an interesting diatom: Helicotheca tamesis (syn. Streptotheca tamesis). It is ribbon-like torted. One cell measured 100µm x 90 µm.
First picture: 20x DIC, stack with 7 pics
second picture: 40x DIC, stack 8 pics
third picture: 20xPh, stack with 8 pics.