• Abas wittii (Grunow) R.Ross & P.A.Sims, 1980 †
• Acanthoceras azoricum (Menegh.) Kütz., 1862 accepted as Ceramium azoricum Meneghini accepted as Ceramium echionotum var. azoricum (Meneghini) Piccone, 1884
• Acanthoceras echinophorum (Menegh.) Frauenf., 1855 accepted as Ceramium echionotum J.Agardh, 1844
• Acanthoceras echionotum (J.Agardh) Kütz., 1849 accepted as Ceramium echionotum J.Agardh, 1844
• Acanthoceras magdeburgense Honigm., 1910 accepted as Acanthoceras zachariasii (Brun) Simonsen, 1979
• Acanthoceras magdeburgense var. lata Honigm., 1909 accepted as Acanthoceras zachariasii (Brun) Simonsen, 1979
• Acanthoceras magdeburgense var. magdeburgense Honigmann, 1909 accepted as Acanthoceras magdeburgense Honigm., 1910 accepted as Acanthoceras zachariasii (Brun) Simonsen, 1979
• Acanthoceras oxyacanthum Kützing, 1849 (uncertain)
• Acanthoceras zachariasii (Brun) Simonsen, 1979
• Acanthodiscus antarcticus Hajós, 1975 †
• Acanthodiscus clypeolus (Brun) Van Heurck, 1896 †
• Acanthodiscus convexus Hajós & Stradner in Hajós, 1975 †
• Acanthodiscus danicus J.Fenner, 1994 †
• Acanthodiscus immaculatus (Hanna) V.A.Nikolaev & J.A.Barron in Nikolaev et al., 2001 †
• Acanthodiscus ornatus Hajós & Stradner in Hajós, 1975 †
• Acanthodiscus paterus (J.A.Long, Fuge & J.Smith) V.A.Nikolajev & Fourt. †
• Acanthodiscus rugosus Pant., 1892 †
• Acanthodiscus schmidtii Jousé, 1951 †
• Acanthodiscus vulcaniformis Jousé, 1951 †
• Achnantella brevipes (C.Agardh) Gaillon, 1833 accepted as Achnanthes brevipes C.Agardh, 1824
• Achnantella longipes (C.Agardh) Gaillon, 1833 accepted as Achnanthes longipes C.Agardh, 1824
• Achnantheiopsis apiculata (R.M.Patrick) Lange-Bert., 1997 accepted as Planothidium apiculatum (R.M.Patrick) Lange-Bertalot, 1999
• Achnantheiopsis aueri (Krasske) Lange-Bert., 1997 † accepted as  †
• Achnantheiopsis biporoma (M.H.Hohn & Hellerman) Lange-Bertalot, 1997 accepted as Planothidium biporomum (M.H.Hohn & Hellerman) Lange-Bertalot, 1999
• Achnantheiopsis borneolanceolata Lange-Bert., 1997 accepted as
• Achnantheiopsis chilensis (Hust.) Lange-Bert., 1997 † accepted as Planothidium chilense (Hustedt) Lange-Bertalot, 1999 † accepted as Achnanthes chilensis Hustedt, 1927 †
• Achnantheiopsis daui (Foged) Lange-Bert., 1997 accepted as Planothidium daui (Foged) Lange-Bertalot, 1999 accepted as Achnanthes daui Foged, 1962
• Achnantheiopsis delicatula (Kütz.) Lange-Bert., 1997 accepted as Planothidium delicatulum (Kützing) Round & Bukhtiyarova, 1996 accepted as Achnanthidium delicatulum f. delicatulum Kützing, 1844
• Achnantheiopsis distincta (Messik.) Lange-Bert., 1997 accepted as Planothidium distinctum (Messikommer) Lange-Bertalot, 1999 accepted as Achnanthes distincta Messikommer, 1954
• Achnantheiopsis dubia (Grunow) Lange-Bert., 1997 accepted as Planothidium dubium (Grunow) Round & Bukhtiyarova, 1996
• Achnantheiopsis engelbrechtii (Cholnoky) Lange-Berta., 1997 accepted as Planothidium engelbrechtii (Cholnoky) Round & L.Bukhtiyarova, 1996 accepted as Achnanthes engelbrechtii var. engelbrechtii Cholnoky, 1955
• Achnantheiopsis fonticolanceolata (Lange-Bert. & Schim.) Lange-Bert., 1997 accepted as Planothidium fonticolanceolatum (Lange-Bertalot & Schimanski) Lange-Bertalot, 1999 accepted as Achnanthes fonticolanceolata Lange-Bertalot & Schimanski, 1989
• Achnantheiopsis fragilarioides (J.B.Petersen) Lange-Bert., 1997 accepted as Planothidium fragilarioides (J.B.Petersen) Round & Bukhtiyarova, 1996 accepted as Achnanthes fragilarioides J.B.Petersen, 1924
• Achnantheiopsis frequentissima (Lange-Bert.) Lange-Bert., 1997 accepted as Planothidium frequentissimum (Lange-Bertalot) Lange-Bertalot, 1999
• Achnantheiopsis frequentissima var. magna (F.Straub) Lange-Bert., 1997 accepted as Planothidium frequentissimum var. magnum (F.Straub) Lange-Bertalot, 1999 accepted as Achnanthes rostrata var. magna F.Straub, 1985
• Achnantheiopsis frequentissima var. minor (Schulz-Danzig) Lange-Bert., 1997 accepted as Planothidium frequentissimum var. minus (Schulz-Danzig) Lange-Bertalot, 1999 accepted as Achnanthes lanceolata f. minor Schulz, 1926
• Achnantheiopsis grana (M.H.Hohn & Hellerman) Lange-Bert., 1997 accepted as Planothidium granum (M.H.Hohn & Hellerman) Lange-Bertalot, 1999 accepted as Achnanthes grana Hohn & Hellerman, 1963
• Achnantheiopsis hauckiana (Grunow) Lange-Bert., 1997 accepted as Planothidium hauckianum (Grunow) Round & Bukhtiyarova, 1996
• Achnantheiopsis haynaldii (Schaarschm.) Lange-Bert., 1997 accepted as Planothidium haynaldii (Schaarschmidt) Lange-Bertalot, 1999
• Achnantheiopsis heteromorpha (Grunow) Lange-Bert., 1997 accepted as Planothidium heteromorphum (Grunow) Lange-Bertalot, 1999 accepted as Achnanthes heteromorpha var. heteromorpha Grunow in Cleve & Grunow, 1880
• Achnantheiopsis holstii (Cleve) Lange-Bert., 1997 accepted as Planothidium holstii (Cleve) Lange-Bertalot, 1999 accepted as Achnanthes holstii var. holstii Cleve, 1881
• Achnantheiopsis joursacensis (Hérib.) Lange-Bert., 1997 accepted as Planothidium joursacense (Héribaud-Joseph) Lange-Bertalot, 1999 accepted as Achnanthes joursacense Héribaud-Joseph, 1903
• Achnantheiopsis lanceolata (Bréb. ex Kütz.) Lange-Bert., 1997 accepted as Planothidium lanceolatum (Brébisson ex Kützing) Bukhtiyarova, 1999
• Achnantheiopsis lanceolatoides (Sovereign) Lange-Bert., 1997
• Achnantheiopsis linkei (Hustedt) Lange-Bert., 1997 accepted as Planothidium linkei (Hustedt) Lange-Bertalot, 1999 accepted as Achnanthes linkei var. linkei Hustedt, 1939
• Achnantheiopsis magnifica (Hustedt) Lange-Bert., 1997 accepted as Planothidium magnificum (Hustedt) Lange-Bertalot, 1999 accepted as Achnanthes magnifica Hustedt, 1952
• Achnantheiopsis marina (Hust.) Lange-Bertalot, 1997 accepted as Planothidium marinum (Hustedt) Lange-Bertalot, 1999 accepted as Achnanthes marina Hustedt, 1937
• Achnantheiopsis minutissima (Krasske) Lange-Bert., 1997 accepted as Achnanthes lanceolata var. minutissima Krasske, 1938 accepted as Planothidium minutissimum (Krasske) Lange-Bertalot, 1999
• Achnantheiopsis miota (J.R.Carter & Denny) Lange-Bert., 1997 accepted as Planothidium miotum (Carter & Denny) Lange-Bertalot, 1999 accepted as Achnanthes miota Carter & Denny, 1982
• Achnantheiopsis oestrupii (Cleve-Euler) Lange-Bert., 1997 accepted as Planothidium oestrupii (A.Cleve) Round & L.Bukhtiyarova, 1996
• Achnantheiopsis peragalloi (Brun & Hérib.) Lange-Bert., 1997 accepted as Planothidium peragalloi (J.Brun & Héribaud-Joseph) Round & L.Bukhtiyarova, 1996
• Achnantheiopsis pericava (J.R.Carter) Lange-Bert., 1997 accepted as Planothidium pericavum (J.R.Carter) Lange-Bertalot, 1999 accepted as Achnanthes pericava J.R.Carter, 1966
• Achnantheiopsis pseudotanensis (Cleve-Euler) Lange-Bert., 1997 accepted as Planothidium pseudotanense (Cleve-Euler) Lange-Bertalot, 1999 accepted as Achnanthes pseudotanensis A.Cleve-Euler, 1953
• Achnantheiopsis pungens (Cleve-Euler) Lange-Bert., 1997 accepted as Planothidium pungens (Cleve-Euler) Lange-Bertalot, 1999 accepted as Achnanthes elliptica var. pungens Cleve-Euler, 1934 accepted as Skabitschewskia pungens (Cleve-Euler) Kulikovskiy & Lange-Bertalot, 2015
• Achnantheiopsis robusta (Hustedt) Lange-Bert., 1997 accepted as Planothidium robustum (Hustedt) Lange-Bertalot, 1999
• Achnantheiopsis robustior Lange-Bertalot, 1997 accepted as Planothidium robustius Lange-Bertalot, 1999
• Achnantheiopsis rostrata (Østrup) Lange-Bert., 1997 accepted as Planothidium rostratum (Østrup) Lange-Bertalot, 1999
• Achnantheiopsis salvadoriana (Hustedt) Lange-Bert., 1997 accepted as Planothidium salvadorianum (Hustedt) Lange-Bertalot, 1999
• Achnantheiopsis septentrionalis (Østrup) Lange-Bert., 1997 accepted as
• Achnanthepyla arctica (Cleve) Perag., 1921 accepted as Achnanthes brevipes var. arctica (P. T. Cleve) T. Ko-Bayashi, 1965 accepted as Achnanthidium arcticum Cleve, 1873
• Achnanthepyla arctica var. incurvata (Østrup) Perag., 1921
• Achnanthepyla baccata Perag., 1921
• Achnanthepyla bongrainii Perag., 1921 accepted as Achnanthes bongrainii (M. Peragallo) Mann, 1937 accepted as Achnanthepyla bongrainii var. bongrainii Perag., 1921
• Achnanthepyla bongrainii var. bongrainii Perag., 1921 accepted as Achnanthepyla bongrainii Perag., 1921 accepted as Achnanthes bongrainii (M. Peragallo) Mann, 1937
• Achnanthepyla bongrainii var. dilatata Perag., 1924
• Achnanthepyla bongrainii var. parallela Perag., 1921 accepted as Achnanthes bongrainii var. parallela (Peragallo) Frenguelli & Orlando, 1958
• Achnanthepyla gainii accepted as Achnanthepyla gainii var. gainii Perag., 1921 accepted as Achnanthes gainii (M. Peragallo) Mann, 1937
• Achnanthepyla gainii var. gainii Perag., 1921 accepted as Achnanthes gainii (M. Peragallo) Mann, 1937
• Achnanthepyla gainii var. ostrupii Perag., 1921
• Achnanthepyla glabrata (Grunow) Perag., 1921
• Achnanthepyla glabrata var. aucklandica (Grunow in Cleve & Grunow) Perag., 1921
• Achnanthepyla glabrata var. glabrata (Grunow) Perag., 1921 accepted as Achnanthepyla glabrata (Grunow) Perag., 1921
• Achnanthepyla groenlandica (Cleve) Perag., 1921 accepted as Achnanthes groenlandica (Cleve) Grunow, 1880
• Achnanthepyla jamalinensis (Grunow in Cleve & Grunow) Perag., 1921 accepted as Achnanthes jamalinensis Grunow in Cleve & Grunow, 1880
• Achnanthepyla mesogongyla (Grunow in Cleve & Grunow) Perag., 1921
• Achnanthepyla minuta ‘(Grunow) M. Peragallo' VanLandingham, 1967 accepted as Achnanthepyla minutula (Grunow) Perag., 1921
• Achnanthepyla minutula (Grunow) Perag., 1921
• Achnanthepyla simplex Perag., 1921
• Achnanthepyla temperei (Perag.) Perag., 1921 accepted as Achnanthes temperei M.Peragallo, 1908
• Achnanthes aapajaervensis A.Cleve, 1934
• Achnanthes aapajärvensis Cleve-Euler, 1934 accepted as Achnanthes aapajaervensis A.Cleve, 1934
• Achnanthes abundans Manguin in Bourrelly & Manguin, 1954 accepted as Psammothidium abundans (Manguin, Bourrelly & Manguin) L.Bukhtiyarova, 1996
• Achnanthes abundans var. abundans Manguin in Bourrelly & Manguin, 1955 accepted as Achnanthes abundans Manguin in Bourrelly & Manguin, 1954 accepted as Psammothidium abundans (Manguin, Bourrelly & Manguin) L.Bukhtiyarova, 1996
• Achnanthes abundans var. elliptica Manguin in Bourrelly & Manguin, 1955 accepted as Psammothidium abundans var. ellipticum (Manguin) R. Flower, 2005
• Achnanthes acares M.H.Hohn & Hellerman, 1963
• Achnanthes acidoclinata Lange-Bert., 1996 accepted as Psammothidium acidoclinatum (Lange-Bertalot) Lange-Bertalot, 1999
• Achnanthes acus Simonsen ex F.Hinz et al., 2012
• Achnanthes acuta Frenguelli, 1953
• Achnanthes adamantiformis (R.E.M.Archibald) R.E.M.Archibald, 1971 accepted as Navigiolum adamantiforme (Archibald) Taylor & Lange-Bertalot
• Achnanthes adamsii Cholnoky, 1964
• Achnanthes adnata Bory, 1822
• Achnanthes affinis Grunow, 1880 accepted as Achnanthidium affine (Grunow) Czarnecki, 1994 accepted as Achnanthes affinis var. affinis Grunow in Cleve & Grunow, 1880
• Achnanthes affinis var. affinis Grunow in Cleve & Grunow, 1880 accepted as Achnanthes affinis Grunow, 1880 accepted as Achnanthidium affine (Grunow) Czarnecki, 1994
• Achnanthes affinis var. bistriata Skvortsov, 1938 accepted as Achnanthes minutissima var. bistriata Skvortzov, 2012
• Achnanthes affinis var. jamalinensis (Grunow in Cleve & Grunow) Cleve, 1895 accepted as Achnanthes jamalinensis Grunow in Cleve & Grunow, 1880
• Achnanthes affinis var. minuta Skvortsov, 1936
• Achnanthes africana Woodhead & Tweed, 1958
• Achnanthes agardhi (Kütz.) Cleve & J.D.Möller accepted as Achnanthes brevipes var. seriata (Agardh) Cleve, 1895 accepted as Achnanthes seriata C.Agardh, 1827
• Achnanthes agardhi f. agardhi (Kütz.) Cleve & J.D.Möller, 1878 accepted as Achnanthes agardhi (Kütz.) Cleve & J.D.Möller accepted as Achnanthes brevipes var. seriata (Agardh) Cleve, 1895 accepted as Achnanthes seriata C.Agardh, 1827
• Achnanthes agardhi f. minuta Cleve & J.D.Möller, 1878 accepted as Cymbosira minutula Grunow, 1863