• Cocconeis communis f. placentula (Ehrenberg) Chmielevski, 1885 accepted as Cocconeis placentula f. placentula Ehrenberg, 1838
• Cocconeis communis var. placentula (Ehrenberg) O.Kirchner, 1878 accepted as Cocconeis placentula f. placentula Ehrenberg, 1838
• Cocconeis pediculus var. placentula (Ehrenberg) Grunow, 1867 accepted as Cocconeis placentula f. placentula Ehrenberg, 1838
• Cocconeis placentula (Skvortzow) Skabichevskii, 1977 (uncertain > unassessed)
• Cocconeis placentula (Skvortzow) Skabichevskii, 1977 accepted as Cocconeis placentula var. baicalensis Skvortzov & Meyer, 1928
• Cocconeis placentula Ehrenberg, 1838
• Cocconeis placentula f. anormalis Østrup, 1910 (uncertain > unassessed)
• Cocconeis placentula f. elata Cleve-Euler, 1934 (uncertain > unassessed)
• Cocconeis placentula f. euglypta (Ehrenberg) Hustedt, 1957 accepted as Cocconeis euglypta Ehrenberg, 1854
• Cocconeis placentula f. intermedia (Heribaud & Peragallo in Heribaud) Cleve, 1895 accepted as Cocconeis intermedia f. intermedia Héribaud & M. Peragallo in Héribaud, 1893
• Cocconeis placentula f. klinoraphis Geitler, 1927 (uncertain > unassessed)
• Cocconeis placentula f. lineata (Ehrenberg) Hustedt, 1957 accepted as Cocconeis lineata Ehrenberg, 1843
• Cocconeis placentula f. major Cleve-Euler, 1953 (uncertain > unassessed)
• Cocconeis placentula f. maximaornata Kaiser, 1918 (uncertain > unassessed)
• Cocconeis placentula f. minor (Pantocsek) F.W. Mills, 1933 accepted as Cocconeis lineata var. minor Pantocsek, 1892
• Cocconeis placentula f. minor Brun & Héribaud in Héribaud, 1893 accepted as Cocconeis intermedia f. minor Peragallo & Héribaud in Héribaud, 1893 † accepted as Cocconeis intermedia Peragallo & Héribaud in Héribaud, 1893 emend C.E.Wetzel, G.G.Lai, Ector & Jüttner in Lai et al., 2020
• Cocconeis placentula f. minuta Cleve in A. Schmidt, 1894 (uncertain > unassessed)
• Cocconeis placentula f. minutissima Mayer, 1913 (uncertain > unassessed)
• Cocconeis placentula f. nipponica Skvortzow, 1936 (uncertain > unassessed)
• Cocconeis placentula f. perpusilla Rabenhorst, 1864 (uncertain > unassessed)
• Cocconeis placentula f. placentula Ehrenberg, 1838 (uncertain > unassessed)
• Cocconeis placentula f. pumila Cleve-Euler, 1953 (uncertain > unassessed)
• Cocconeis placentula f. rouxii (Héribaud & Brun in Héribaud) Cleve-Euler, 1953 accepted as Cocconeis rouxii var. rouxii Héribaud & Brun in Héribaud, 1893
• Cocconeis placentula f. trilineata (M. Peragallo & Héribaud in Héribaud) Cleve-Euler, 1953 accepted as Cocconeis trilineatus M. Peragallo & Héribaud in Héribaud, 1893
• Cocconeis placentula var. acuta Meister, 1934 (uncertain > unassessed)
• Cocconeis placentula var. australica Playfair, 1914 (uncertain > unassessed)
• Cocconeis placentula var. baicalensis Skvortzov & Meyer, 1928 (uncertain > unassessed)
• Cocconeis placentula var. baikalensis Skvortzow, 1937 (uncertain > unassessed)
• Cocconeis placentula var. baltica Juhlin-Dannfelt, 1882 (uncertain > unassessed)
• Cocconeis placentula var. chiemensis Kaiser, 1926 (uncertain > unassessed)
• Cocconeis placentula var. constricta Zanon, 1948 (uncertain > unassessed)
• Cocconeis placentula var. costata Brun, 1880 (uncertain > unassessed)
• Cocconeis placentula var. elata (Cleve-Euler) Cleve-Euler, 1953 accepted as Cocconeis placentula f. elata Cleve-Euler, 1934
• Cocconeis placentula var. elliptica Hoppe, 1926 (uncertain > unassessed)
• Cocconeis placentula var. euglypta (Ehrenberg) Grunow, 1884 accepted as Cocconeis euglypta Ehrenberg, 1854
• Cocconeis placentula var. euglyptoides L.Geitler, 1958 (uncertain > unassessed)
• Cocconeis placentula var. fossilis Pantocsek, 1902 (uncertain > unassessed)
• Cocconeis placentula var. genuina Mayer, 1913 (uncertain > unassessed)
• Cocconeis placentula var. gibba Kaiser, 1918 (uncertain > unassessed)
• Cocconeis placentula var. gonzalezguerreroi Camara, 1950 (uncertain > unassessed)
• Cocconeis placentula var. inclyta Schmidt in Schmidt et al., 1894 (uncertain > unassessed)
• Cocconeis placentula var. intermedia (Héribaud & M.Peragallo) Cleve, 1895 accepted as Cocconeis intermedia Peragallo & Héribaud in Héribaud, 1893 emend C.E.Wetzel, G.G.Lai, Ector & Jüttner in Lai et al., 2020
• Cocconeis placentula var. intermedia f. minor (Héribaud & M. Peragallo) Cleve, 1895 accepted as Cocconeis intermedia Peragallo & Héribaud in Héribaud, 1893 emend C.E.Wetzel, G.G.Lai, Ector & Jüttner in Lai et al., 2020
• Cocconeis placentula var. klinoraphis Geitler, 1927
• Cocconeis placentula var. limpida Schmidt in Schmidt et al., 1894 (uncertain > unassessed)
• Cocconeis placentula var. lineata (Ehrenberg) van Heurck, 1885 accepted as Cocconeis lineata Ehrenberg, 1843
• Cocconeis placentula var. lineolata Yakovlev, 1924 (uncertain > unassessed)
• Cocconeis placentula var. meridionalis Brun in Schmidt et al., 1894 (uncertain > unassessed)
• Cocconeis placentula var. minor (Brun & Héribaud in Héribaud) Héribaud accepted as Cocconeis placentula f. minor Brun & Héribaud in Héribaud, 1893 accepted as Cocconeis intermedia f. minor Peragallo & Héribaud in Héribaud, 1893 † accepted as Cocconeis intermedia Peragallo & Héribaud in Héribaud, 1893 emend C.E.Wetzel, G.G.Lai, Ector & Jüttner in Lai et al., 2020
• Cocconeis placentula var. minor H. Peragallo in Pelletan, 1889 (uncertain > unassessed)
• Cocconeis placentula var. oblonga Skvortzov, 2012 (uncertain)
• Cocconeis placentula var. oceanica (Ehrenberg) Schumann, 1867 accepted as Cocconeis oceanica Ehrenberg, 1840
• Cocconeis placentula var. placentula (M. Peragallo & Heribaud in Héribaud) Kolbe, 1927 accepted as Cocconeis trilineatus M. Peragallo & Héribaud in Héribaud, 1893
• Cocconeis placentula var. placentula Ehrenberg, 1838
• Cocconeis placentula var. placentula Rabenhorst, 1864 (uncertain > unassessed)
• Cocconeis placentula var. placentula Rishaw, 1870 (uncertain > unassessed)
• Cocconeis placentula var. pseudolineata Geitler, 1927 (uncertain > unassessed)
• Cocconeis placentula var. punctata (Ehrenberg) Brun, 1880 accepted as Cocconeis punctata Ehrenberg, 1841
• Cocconeis placentula var. punctata T.Morobuse (uncertain > unassessed)
• Cocconeis placentula var. ranomafanensis E. Manguin, 1952 (uncertain > unassessed)
• Cocconeis placentula var. rodriguensis C.Riaux-Gobin, O.E.Romero, P.Compère & A.Y.Al-Handal, 2011
• Cocconeis placentula var. rotunda Hajós, 1968 (uncertain > unassessed)
• Cocconeis placentula var. rotunda Skvortzow, 1929 (uncertain > unassessed)
• Cocconeis placentula var. rouxii (Héribaud-Joseph & Brun) Cleve, 1895 accepted as Cocconeis rouxii var. rouxii Héribaud & Brun in Héribaud, 1893
• Cocconeis placentula var. siberica Skabichevskii, 1952 (uncertain > unassessed)
• Cocconeis placentula var. skvortzowii (Skvortzow) Skabichevskii (uncertain > unassessed)
• Cocconeis placentula var. tenustriata Geitler, 1932 (uncertain > unassessed)
• Cocconeis placentula var. trilineata (M. Peragallo & Héribaud in Héribaud) Cleve, 1895 accepted as Cocconeis trilineatus M. Peragallo & Héribaud in Héribaud, 1893