Gomphonema angustatum var. obtusatum has a more clavate shape.
Gomphonema parvulum has a more rhombic-lanceolate valve shape and more rostrate apices.
Gomphonema micropus may appear very similar, but the areolae along the axial area are not expanded. The valves of G. micropus are also more elliptic-lanceolate. It needs to be determined if G.angustatum is the fine striae form of G. sarcophagus, as these taxa may be indistinguishable.