Cytomorphological characters supporting the taxonomic validity of Cyanothece (Cyanoprokaryota)

The fine structure of the type species of the genus Cyanothece KOMAREK 1976, C. aeruginosa, is described and compared with the main cytological characteristics of morphologically related members of the genera Cyanobium, Cyanobacterium and Synechococcus. Several morphological features, such as cell walls with thick outer layers containing a special type of vesicles, position of thylakoids, "keritomy" (net-like appearance of protoplast caused by arrangement of thylakoids, net-like nucleoids and/or by tendency to form intrathylakoidal spaces) and a special structure of mucilaginous envelopes were found to be characteristic of this genus, supporting its separate position among coccal cyanoprokaryotes (cyanobacteria, cyanophytes). The taxonomic significance of ultrastructural features in all mentioned genera is discussed.