filaments are usually in large, screw-like coils that do not
have a mucous sheath. They may be solitary and free-floating
plankton or grouped into slimy benthic clumps colored blue- green,
olive-green, or reddish-brown. Each trichome is cylindrical,
isopolar, and may be long or short. Arthrospira is usually
nonmotile, but occasionally glides with a rotating motion. Each
cell has visible cross walls and special
pore patterns in the cell wall, including a row of pores circling
the cell. The apical or end cells are rounded
or cylindrical and may have calyptras or thickened walls. The
thylakoids are arranged radially or in a whirled pattern. A few
species have gas vesicles.
Some researchers think Arthrospira
should be included within the genus Spirulina. A. maxima
and A. fusiformis are also known as Spirulina platensis
and are mass cultivated commercially.
Note how changing
the focus slightly allows different cellular structures to be
viewed on the same specimen.