Pseudanabaena arcuata (Skuja) Anagnostidis et Komárek

Trichomes solitary (very rarely clusters of a few trichomes), short, ± straight or curved (arcuated), (2-) 5-7 (-15)-celled, 10-20 (-80) urn long, immotile, surrounded by mucilaginous, gelatinous, amorphous, diffluent sheaths, irregularly situated or somewhat parallel arranged, 0.9-1.3 um wide, clearly constricted at the hyaline cross-walls, not attenuated at the ends. Cells cylindrical, pale blue-green to pale grey-olive-green, 2-14 um long; cell content homogeneous or finely granulated. Apical cell acute, cylindrical and conical, or slightly truncate, without calyptra.
Occurrence: Freshwater, endogloeic in mucilaginous layer of planktic Rotatoria (Conochilus) in large lakes, also rarely in slime of Microcystis (especially M. flos-aquae) and other species; free-floating (epiplanktic) specimens from mucilaginous, irregular-shaped flakes must be revised; Europe: lakes of Denmark, Germany, Sweden, Switzerland, data from Greece are uncertain