Nitzschia angustata has been sometimes placed in Tryblionella. Nitzschia angustata, however, lacks the longitudinal fold of most species in Tryblionella. Nitzschia angustata var. acuta has strongly rostrate apices. Nitzschia angustatula is more narrow (around 4 μm) and shorter in length (13-24 μm). Tryblionella brunoi is larger and more broad (9-13 µm), has a longitudinal undulation and has coarser areolae, 20 in 10 μm. Nitzschia siliqua has capitate apices.