• Abas wittii (Grunow) R.Ross & P.A.Sims, 1980 †: phytoplankton
• Abratopdinium cardioforme S.Mao & B.A.R.Mohr †: phytoplankton
• Abratopdinium kerguelense S.Mao & B.A.R.Mohr †: phytoplankton
• Abruptophycus compositus Vologdin, 1962 †: phytoplankton
• Acaciella angepena W.V.Preiss, 1972 †: phytoplankton
• Acaciella augusta W.V.Preiss, 1972 †: phytoplankton
• Acaciella australica (Howchin) M.R.Walter, 1972 †: phytoplankton
• Acaciella savoryensis K.Grey & M.R.Walter, 1994 †: phytoplankton
• Acanthina bullosa Korde, 1973 †: phytoplankton
• Acanthina multiformis Korde, 1973 †: phytoplankton
• Acanthoceras zachariasii (Brun) Simonsen, 1979: phytoplankton
• Acanthodinium caryophyllum Kofoid, 1907: phytoplankton
• Acanthodiscus antarcticus Hajós, 1975 †: phytoplankton
• Acanthodiscus clypeolus (Brun) Van Heurck, 1896 †: phytoplankton
• Acanthodiscus convexus Hajós & Stradner in Hajós, 1975 †: phytoplankton
• Acanthodiscus danicus J.Fenner, 1994 †: phytoplankton
• Acanthodiscus immaculatus (Hanna) V.A.Nikolaev & J.A.Barron in Nikolaev et al., 2001 †: phytoplankton
• Acanthodiscus ornatus Hajós & Stradner in Hajós, 1975 †: phytoplankton
• Acanthodiscus paterus (J.A.Long, Fuge & J.Smith) V.A.Nikolajev & Fourt. †: phytoplankton
• Acanthodiscus rugosus Pant., 1892 †: phytoplankton
• Acanthodiscus schmidtii Jousé, 1951 †: phytoplankton
• Acanthodiscus vulcaniformis Jousé, 1951 †: phytoplankton
• Acanthogonyaulax acanthosphaera (Sargeant) Sargeant †: phytoplankton
• Acanthogonyaulax paliuros (Sargeant) Sargeant †: phytoplankton
• Acanthogonyaulax spinifera (Murray & Whitting) H.W.Graham, 1942: phytoplankton
• Acanthoica acanthifera Lohmann ex Lohmann, 1913: phytoplankton
• Acanthoica acanthos J.Schiller, 1925: phytoplankton
• Acanthoica bidentula Lecal-Schlauder, 1951: phytoplankton
• Acanthoica biscayensis A.Kleijne, 1992: phytoplankton
• Acanthoica coronata Lohmann, 1903: phytoplankton
• Acanthoica janchenii J.Schiller, 1925: phytoplankton
• Acanthoica lithostratos J.Schiller, 1926: phytoplankton
• Acanthoica maxima Heimdal, 1981: phytoplankton
• Acanthoica monospina J.Schiller, 1925: phytoplankton
• Acanthoica ornata Conrad, 1928: phytoplankton
• Acanthoica quattrospina Lohmann, 1903: phytoplankton
• Acanthoica rubens Kamptner, 1941: phytoplankton
• Acanthoica schilleri Conrad, 1928: phytoplankton
• Acanthoica trispinosa Ostenfeld: phytoplankton
• Acantholithium dicopum Haeckel, 1887: phytoplankton
• Acantholithium stellatum Haeckel, 1887: phytoplankton
• Acanthonia echinoides (Claparède & Lachmann, 1858) Haeckel, 1881: phytoplankton
• Acanthosphaera actinota Haeckel, 1860: phytoplankton
• Acanthosphaera castanea Haeckel, 1887: phytoplankton
• Acanthosphaera dodecastyla Mast, 1910: phytoplankton
• Acanthosphaera pinchuda Boltovskoy, 1980: phytoplankton
• Acanthosphaera tenuis Haeckel, 1887: phytoplankton
• Acaryochloris thomasi Partensky & al., 2018: phytoplankton
• Achnanthepyla baccata Perag., 1921: phytoplankton
• Achnanthepyla glabrata (Grunow) Perag., 1921: phytoplankton
• Achnanthepyla mesogongyla (Grunow in Cleve & Grunow) Perag., 1921: phytoplankton
• Achnanthepyla minutula (Grunow) Perag., 1921: phytoplankton
• Achnanthepyla simplex Perag., 1921: phytoplankton
• Achnanthes aapajaervensis A.Cleve, 1934: phytoplankton
• Achnanthes acares M.H.Hohn & Hellerman, 1963: phytoplankton
• Achnanthes acus Simonsen ex F.Hinz et al., 2012: phytoplankton
• Achnanthes acuta Frenguelli, 1953: phytoplankton
• Achnanthes adamsii Cholnoky, 1964: phytoplankton
• Achnanthes adnata Bory, 1822: phytoplankton
• Achnanthes africana Woodhead & Tweed, 1958: phytoplankton
• Achnanthes agglutinata Grunow in Cleve & Grunow, 1880: phytoplankton
• Achnanthes ambigua S.J.C.Zimmermann, 1918: phytoplankton
• Achnanthes americana Cleve, 1893: phytoplankton
• Achnanthes amphicephala Hust., 1939: phytoplankton
• Achnanthes anceps A.Cleve, 1934: phytoplankton
• Achnanthes annulifera A.Cleve, 1953: phytoplankton
• Achnanthes antarctica Perag., 1921: phytoplankton
• Achnanthes antiqua Lauby, 1910 †: phytoplankton
• Achnanthes apiculata (Greville, 1859): phytoplankton
• Achnanthes araucaniana Freng., 1934 †: phytoplankton
• Achnanthes arcuata (Lyngb.) Kütz., 1833: phytoplankton
• Achnanthes arenaria Amossé, 1941: phytoplankton
• Achnanthes arenicola J.W.Bailey, 1851: phytoplankton
• Achnanthes arguta Hust.ex Simonsen, 1987: phytoplankton
• Achnanthes armillaris (O.F.Müller) Guiry, 2019: phytoplankton
• Achnanthes astridii VanLand., 1967: phytoplankton
• Achnanthes asymbasia M.H.Hohn, 1966: phytoplankton
• Achnanthes asymetrica R.M.Patrick, 1936: phytoplankton
• Achnanthes atacamae Hust., 1927: phytoplankton
• Achnanthes athenais Pant., 1902 †: phytoplankton
• Achnanthes aubertii Hérib., 1920 †: phytoplankton
• Achnanthes australis Ehrenb., 1854: phytoplankton
• Achnanthes baccata (Leud.-Fortm.) Cleve, 1895: phytoplankton
• Achnanthes bacescui Bodeanu, 1976: phytoplankton
• Achnanthes bacillaris Ehrenberg, 1844: phytoplankton
• Achnanthes bacillum Perag. in Héribaud et al., 1920: phytoplankton
• Achnanthes baicaliana Frenguelli, 1953: phytoplankton
• Achnanthes baldjicki sensu Pantocsek, 1892 †: phytoplankton
• Achnanthes baltalensis H.P.Gandhi ex Karthick, 2020 †: phytoplankton
• Achnanthes bavarica Ehrenb., 1853: phytoplankton
• Achnanthes bengalensis Grunow in Cleve & Grunow, 1880: phytoplankton
• Achnanthes bergianii A.Cleve, 1953: phytoplankton
• Achnanthes bergii A.Cleve, 1953: phytoplankton
• Achnanthes bernieri Manguin ex Kociolek & de Reviers, 1996: phytoplankton
• Achnanthes bonaeaurae Zanon, 1949: phytoplankton
• Achnanthes brevipes C.Agardh, 1824: phytoplankton
• Achnanthes calamae Frenguelli, 1930: phytoplankton
• Achnanthes coarctata (Brébisson ex W.Smith) Grunow, 1880: phytoplankton
• Achnanthes confusa Manguin: phytoplankton
• Achnanthes congolensis Hustedt, 1949: phytoplankton