Pseudanabaena Lauterborn, 1915

Key # 7

  1.) Classification: Order Synechococcales, Family Pseudanabaenaceae.

        More than 30 species have been described. The members of Pseudanabaena occupy an

        extremely wide range of habitats. The results of some preliminary studies of their genetic

        material suggest that revision and reclassification of some species is needed,

        but this has not been entirely clarified (Komárek and Johansen 2015b).

  2.) Form: Filamentous.

  3.) Groups: Filaments are solitary or agglomerated into very fine, mucilaginous mats.

  4.) Sheaths: No firm sheath but rarely a fine, colorless, diffluent, narrow mucilage envelope.

  5.) Filaments: Short, unbranched, straight to arcuate, unattenuated; older filaments have

        obvious crosswall constrictions; some indistinct motility (trembling or slow gliding).

  6.) Cells: Cylindrical, longer than wide, 1–3.5μm wide; conical end cells, no wall thickening.

        Heterocysts: Absent.

        Akinetes: Absent.

        Aerotopes: Normally absent; some variability.

  7.) Color: Includes various shades of dull green through blue green.

  8.) Replication: Hormogonia production (single to multicellular) or filament disintegration

        without necridia. Division is perpendicular to the long axis, sometimes asymmetrical.

        Cells grow to their original size and shape before the next division.

  9.) Habitat: Mostly planktonic, but also found in metaphytic, periphytic, and benthic habitats

        of lakes with variable trophic levels (oligotrophic to slightly eutrophic).

        Others occur in soil or within algal mucilage or colonial rotifers (endogloeic).

        A few are found in extreme biotopes (mineral/ hot springs or hypersaline habitats).

10.) Similar genera: Anabaena. Both have similar cylindrical cells and moniliform filaments.

        Pseudanabaena cells are more cylindrical and have no heterocysts, akinetes, or sheath.

        Anabaena cells are more rounded and have heterocysts, akinetes, and a colonial sheath.

11.) Toxins: None are reported.

12.) Distinguishing features: Pseudanabaena cells are cylindrical and have conspicuous,

        deep crosswall constrictions and no heterocysts, akinetes, or sheath.

        Filaments are moniliform and do not attenuate or narrow toward the ends.  MAN

Pseudanabaena_01

Pseudanabaena is a group of filamentous cyanobacteria. The filaments are short

with no sheath, straight to arcuate (bent like a bow), never tapering and

indistinctly motile. Older filaments have obvious crosswall constrictions.  They

vary from solitary filaments to fine, mucilaginous mats. The cells are cylindrical

and longer than wide. The end cells can be conical. No heterocysts, akinetes or

aerotopes. They are mostly planktonic but can be found in the metaphyton or

periphyton of oligotrophic to slightly eutrophic lakes. This is from a plankton

tow taken from Camp Ernst Lake, Burlington, KY, USA on August 27, 2015.

400X Magnification.

Pseudanabaena_02

This specimen was in a shallow water sample from north shore of Lake Yambo,

Ecuador, taken in 2014. 400X Magnification.

Pseudanabaena_03

This is from a plankton tow taken from Redbud Lake (end of Cedar Hill Lane,

Florence, KY, USA, 39° 0'44.23"N, 84°41'8.61"W) on September 24, 2014.

400X Magnification.