Gomphonema duplipunctatum may be distinguished from G. parvulum and other small species of Gomphonema by its rhombic-lanceolate valves, unprotracted apices, and the two isolated stigmoids in the central area. Gomphonema germainii is similar outline and stria density but differs by having a single stigmoid. Gomphonema signyensis also has two stigmoids and overlaps in size, but differs in valve outline.
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Krammer and Lange-Bertalot 2/4 Pl 76 Fig 1-7