Abadehellidae Loeblich & Tappan, 1984 † (basis of record)
Abadehellidae Loeblich & Tappan, 1984 † (extant flag source)
Abadehellidae Loeblich & Tappan, 1984 † (habitat flag source)
Abadiellidae Hupé, 1953 † (habitat flag source)
Abelisauridae Bonaparte & Novas, 1985 † (extant flag source)
Abelisauridae Bonaparte & Novas, 1985 † (habitat flag source)
Abrocomidae Miller & Gidley, 1918 (extant flag source)
Abrocomidae Miller & Gidley, 1918 (habitat flag source)
Abrograptidae Mu, 1958 † (basis of record)
Abrograptidae Mu, 1958 † (extant flag source)
Abrograptidae Mu, 1958 † (habitat flag source)
Acadiocarididae Schram, 1974 † (basis of record)
Acadiocarididae Schram, 1974 † (extant flag source)
Acadiocarididae Schram, 1974 † (habitat flag source)
Acanthaceae de Jussieu, 1789 (habitat flag source)
Acanthastrellidae Schrammen, 1924 † (basis of record)
Acanthastrellidae Schrammen, 1924 † (extant flag source)
Acanthastrellidae Schrammen, 1924 † (habitat flag source)
Acanthisittidae Sundevall, 1872 (extant flag source)
Acanthisittidae Sundevall, 1872 (habitat flag source)
Acanthoceratidae Hyatt, 1900 † (extant flag source)
Acanthoceratidae Hyatt, 1900 † (habitat flag source)
Acanthochaetetidae Fischer, 1970 (extant flag source)
Acanthochaetetidae Fischer, 1970 (habitat flag source)
Acanthochitonidae Pilsbry, 1893 (extant flag source)
Acanthochitonidae Pilsbry, 1893 (habitat flag source)
Acanthocladiidae Zittel, 1880 † (basis of record)
Acanthocladiidae Zittel, 1880 † (extant flag source)
Acanthocladiidae Zittel, 1880 † (habitat flag source)
Acanthocnemidae Crowson, 1964 (extant flag source)
Acanthocnemidae Crowson, 1964 (habitat flag source)
Acanthodesmiidae Hertwig, 1879 accepted as Trissocyclidae Haeckel, 1881 (extant flag source)
Acanthodesmiidae Hertwig, 1879 accepted as Trissocyclidae Haeckel, 1881 (habitat flag source)
Acanthodidae Huxley, 1861 † (basis of record)
Acanthodidae Huxley, 1861 † (extant flag source)
Acanthodidae Huxley, 1861 † (habitat flag source)
Acanthodontidae Lindström, 1970 † (basis of record)
Acanthodontidae Lindström, 1970 † (habitat flag source)
Acanthograptidae † (extant flag source)
Acanthograptidae † (habitat flag source)
Acanthonematidae Wenz, 1938 † (basis of record)
Acanthonematidae Wenz, 1938 † (habitat flag source)
Acanthosomatidae Signoret, 1864 (extant flag source)
Acanthosomatidae Signoret, 1864 (habitat flag source)
Acanthostegidae Jarvik, 1952 † (extant flag source)
Acanthostegidae Jarvik, 1952 † (habitat flag source)
Acanthuridae Bonaparte, 1835 (extant flag source)
Acaridae Ewing & Nesbitt, 1942 (extant flag source)
Acaridae Ewing & Nesbitt, 1942 (habitat flag source)
Acaroceratidae Chen, Qi & T.E. Chen, 1979 † accepted as Novacaroceratidae Özdikmen, 2013 † (basis of record)
Acaroceratidae Chen, Qi & T.E. Chen, 1979 † accepted as Novacaroceratidae Özdikmen, 2013 † (extant flag source)
Acaroceratidae Chen, Qi & T.E. Chen, 1979 † accepted as Novacaroceratidae Özdikmen, 2013 † (habitat flag source)
Acartophthalmidae Czerny, 1928 (extant flag source)
Acartophthalmidae Czerny, 1928 (habitat flag source)
Acavidae Pilsbry, 1895 (extant flag source)
Acavidae Pilsbry, 1895 (habitat flag source)
Accipitridae Viellot, 1816 (extant flag source)
Accipitridae Viellot, 1816 (habitat flag source)
Acentrophoridae † (basis of record)
Acentrophoridae † (extant flag source)
Acentrophoridae † (habitat flag source)
Aceraceae de Jussieu, 1789 accepted as Sapindaceae de Jussieu, 1789 (extant flag source)
Aceraceae de Jussieu, 1789 accepted as Sapindaceae de Jussieu, 1789 (habitat flag source)
Acervulariidae † (extant flag source)
Acervulariidae † (habitat flag source)
Acervulinidae Schultze, 1854 (habitat flag source)
Acervulinidae Schultze, 1854 (extant flag source)
Achatinellidae Gulick, 1873 (extant flag source)
Achatinellidae Gulick, 1873 (habitat flag source)
Achatinidae Swainson, 1840 (extant flag source)
Achatinidae Swainson, 1840 (habitat flag source)
Acherontiscidae Carroll, 1967 † (basis of record)
Acherontiscidae Carroll, 1967 † (extant flag source)
Acherontiscidae Carroll, 1967 † (habitat flag source)
Achilidae Stål, 1866 (extant flag source)
Achilidae Stål, 1866 (habitat flag source)
Achipteriidae Thor, 1929 (basis of record)
Achipteriidae Thor, 1929 (extant flag source)
Achipteriidae Thor, 1929 (habitat flag source)
Achistridae Frizzell & Exline, 1955 † (basis of record)
Achistridae Frizzell & Exline, 1955 † (extant flag source)
Achistridae Frizzell & Exline, 1955 † (habitat flag source)
Achnanthaceae Kützing, 1844 (extant flag source)
Achorocyathidae Yankauskas, 1965 † (basis of record)
Achorocyathidae Yankauskas, 1965 † (habitat flag source)
Aciculidae Gray, 1850 (extant flag source)
Aciculidae Gray, 1850 (habitat flag source)
Acipenseridae Bonaparte, 1831 (extant flag source)
Acleistoceratidae Flower in Flower & Krummel, 1950 † (extant flag source)
Acleistoceratidae Flower in Flower & Krummel, 1950 † (habitat flag source)
Acleistorhinidae Daly, 1969 † (basis of record)
Acleistorhinidae Daly, 1969 † (extant flag source)
Acleistorhinidae Daly, 1969 † (habitat flag source)
Aclididae G.O. Sars, 1878 (extant flag source)
Aclididae G.O. Sars, 1878 (habitat flag source)
Acmaeidae Forbes, 1850 (extant flag source)
Acmaeidae Forbes, 1850 (habitat flag source)
Acolocrinidae Brett, 1980 † (basis of record)
Acolocrinidae Brett, 1980 † (extant flag source)
Acolocrinidae Brett, 1980 † (habitat flag source)

 Taxonomic remark

 for Coleolida †

Assigned to class Tentaculita in Bouček, 1964; Benton (1993) treats this order simply as "Problematica". Dernov, 2022 ... [details]

 Taxonomic remark

 for Eobacterium E.S. Barghoorn & J.W. Schopf, 1966

Included as an accepted genus of fossil Bacteria in Armstrong & Brasier, 2013, however Williams, 2012 states that ... [details]

 Taxonomic remark

 for Hyolitha †

Treated as a phylum in Runnegar, 1980 and PaleoBioDB (2017); other sources treat as an extinct class of Mollusca ... [details]

 Taxonomic remark

 for Paraconodontida †

Included in Benton, 1993 as questionably within class Conodonta; some more recent works exclude them altogether, ... [details]