Euastrum oblongum is a species of desmid, in the family Desmidiaceae.

[1] Euastrum oblongum consists of cells that are elliptic in outline, divide into two halves called semicells.

Semicells have a pair of basal lobes and a pair of lateral lobes, both with a shallow "pit" as to appear double-lobed.

The apex is truncate with a deep notch.

[2] Euastrum oblongum occurs in mesotrophic waters.