Hmm, it’s true, then. They are here. Tychonema‘s. On the Cyanobactria course in Czech Rebublic last August I was quite surprised to hear Prof. Komárek say that Tychonema is quite common in the northern lakes…
As he, together with Anagnostidis, wrote in Süsswasserflora 19/2 (2005) they occur “in the plankton of northern, colder lakes, slightly eutrophicated”. Found some in a northern lake.
Tychonema resembles a lot Planktothrix, and is very closely related too. Both belong to the family Phormidiacea and even to the subfamily Phormidioideae. What is different between these genera is that in Tychonema the cell content is pale and whit “holes” These holes are in fact widened thylakoids, a phenomenon called keritomy.
Tychonema bourrellyi (J.W.G.Lund) Anagnostidis & Komárek
Komárek, J. & Anagnostidis, K. 2007. Cyanoprokaryota , 2. Teil: Oscillatoriales. Süßwasserflora von Mitteleuropa, Band. 19/2. Elsevier, München.