Species: Colonies sometimes surrounded by mucilage; cell body cylindrical to spool-shaped, with broadly rounded ends
and slightly concave sides, 10-21 μm long, 3-8 μm wide;
cells arranged in a linear series contacting at the polar regions of the sides making intercellular perforation
between the cells; outer cells with slightly convexed outer side and a long, slightly curved spine at each corner;
cell wall smooth or punctate
(Photomicrographs of the Freshwater Algae, vol. 16, 1996).
* Preliminary DNA analyses showed that stock Ffu-1, an isolate from these cells, is not belong to S. perforatus, but to S. tropicus. Ffu-1 may belong to an intermediate type between both species (communicated by Dr. E. Hegewald at Research Centre Jülich, ICG III Phytosphere, Germany, December 2005).