Staurastrum polytrichum. Notice large cell dimensions and stout spines that are evenly distributed over the cell surface.
Cell dimensions (L x B): ca 80 x 80 µm (including spines)
S. polytrichum is a conspicuous, 3-radiate Staurastrum species. Semicells are elliptic in outline and the cell wall is evenly covered with stout spines arranged in obscure circles around the angles. In apical view semicells are triangular with straight sides and broadly rounded angles. S. polytrichum is characteristic of shallow, slightly acidic, mesotrophic waters. In the Netherlands it is a rare species nowadays only to be encountered in some quaking fens in the Holocene part of the country.