• Nitzschia distans var. sigmoidea Grunow in Cleve & Grunow, 1880 (uncertain > unassessed)
• Nitzschia incolor var. sigmoidea Mereschkowsky, 1902 (uncertain > unassessed)
• Nitzschia obtusa var. sigmoidea Østrup, 1910 (uncertain > unassessed)
• Nitzschia praelonga var. sigmoidea Cleve-Euler, 1939 (uncertain > unassessed)
• Nitzschia putrida var. sigmoidea Mereschkowsky, 1903 (uncertain > unassessed)
• Nitzschia quarnerensis var. sigmoidea Grunow, 1862 (uncertain > unassessed)
• Nitzschia sigmoidea (Nitzsch) W.Smith, 1853
• Nitzschia sigmoidea Østrup, 1910 (uncertain > unassessed)
• Nitzschia sigmoidea var. amoricana (Kützing) Brébisson, 1870 (uncertain > unassessed)
• Nitzschia sigmoidea var. armoricana (Kützing) Grunow in Cleve & Grunow, 1880 accepted as Synedra armoricana Kützing, 1844
• Nitzschia sigmoidea var. balatonis Pantocsek, 1902 (uncertain > unassessed)
• Nitzschia sigmoidea var. beta W. Smith, 1853 (uncertain > unassessed)
• Nitzschia sigmoidea var. brebissonii (Kützing) Rabenhorst, 1864 accepted as Sigmatella brebissonii Kützing, 1849
• Nitzschia sigmoidea var. genuina Cleve-Euler, 1952 (uncertain > unassessed)
• Nitzschia sigmoidea var. genuina Mayer, 1913 (uncertain > unassessed)
• Nitzschia sigmoidea var. reflexa Carruthers, 1864 (uncertain > unassessed)
• Nitzschia sigmoidea var. sigmatella (Gregory) (uncertain > unassessed)
• Nitzschia sigmoidea var. sigmoidea (Nitzsch) W. Smith, 1853 accepted as Bacillaria sigmoidea Nitzsch, 1817
• Nitzschia sigmoidea var. subtilis Gordienko, 1929 (uncertain > unassessed)
• Nitzschia sigmoidea var. undulata Petit, 1877 (uncertain > unassessed)
• Nitzschia tenuis var. sigmoidea Arnott in Grunow, 1880 (uncertain > unassessed)