Cell outline has a deep constriction that divides the cell into two approx. equal semicells
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Cell not flattened; "arms" emerge from the end of each semi-cell and are radially arranged if view end-on.
Staurastrum -
Semi-cells rounded; constriction deep or wide; cell outline relatively smooth except for short spines (cf. Cosmarium).
Staurodesmus -
Semi-cells ovoid to slightly polygonal, each ornamented by at least 4 spines arising at 90 degress to the cell surface.
Xanthidium -
Semi-cells long and cylindrical (with wavy outline in some species), with swelling near constriction.
Pleurotaenium -
Cell flattened in end or side view; semi-cells composed of radiating "arms", all in one plane.
Micrasterias -
Semi-cells rounded, often with rough or warty surface, but spines do not occur.
Cosmarium -
Semi-cells usually longer than wide, with prominent lobes, and a notch at the end of each one.
Euastrum -
Cells small, hourglass shaped, with a spine at each corner.
Arthrodesmus