- Abarenicola Wells 1959
- Abbottina D.S. Jordan & Fowler 1903
- Abies P. Miller 1754
- Ablennes Jordan & Fordice 1887
- Abudefduf Forsskål 1775
- Abyssorhynchia Zezina 1980
- Abyssothyris Thomson 1927
- Acalypha Linné 1753
- Acalypta Westwood 1840
- Acanthaster Gervais 1841
- Acanthastrea Milne-Edwards & Haime 1848
- Acanthephyra A. Milne-Edwards 1881
- Acanthobasiliola Zezina 1981
- Acanthocephalus Koelreuter 1771
- Acanthocepola Bleeker 1874
- Acanthochitona Gray 1821
- Acanthochondria Oakley 1930
- Acanthocybium Gill 1862
- Acanthocyclops Kiefer 1927
- Acanthogobius Gill 1859
- Acanthopagrus Peters 1855
- Acanthopanax (Decaisne & Planchon) F.A.W. Miquel
- Acanthopleura Guilding 1829
- Accipiter Brisson 1760
- Acentrogobius Bleeker 1874
- Acentronura Kaup 1853
- Acer Linné 1753
- Acharax Dall 1908
- Acheilognathus Bleeker 1863
- Achelia Hodge 1864
- Achyranthes Linné 1753
- Aciconula Mayer 1903
- Acila H. & A. Adams 1858
- Acipenser Linnaeus 1758
- Acorus Linné 1753
- Acrepyris Kieffer 1905
- Acrocephalus J.A. Naumann & J.F. Naumann 1811
- Acrocirrus Grube 1873
- Acromycter Smith & Kanazawa 1977
- Acropyga Roger 1862
- Acropoma Temminck & Schlegel 1843
- Acropora Oken 1815
- Actinocleidus Mueller 1937
- Actinopyga Bronn 1860
- Acuaria Bremser 1811
- Acupalpus Latreille 1829
- Acusta Albers 1860
- Aedes Meigen 1818
- Aeginellopsis Arimoto 1970
- Aegista Albers 1850
- Aegisthus Giesbrecht 1891
- Aerothyris Allan 1939
- Aesculus Linné 1753
- Aesopia Kaup 1858
- Aetheia Thomson 1915
- Aetobatus Blainville 1816
- Aetomylaeus Garman 1908
- Agabus Leach 1817
- Agamomermis Stiles 1903
- Agelas Duchassaing & Michelotti 1864
- Agonum Bonelli 1810
- Agriocnemis Sélys 1877
- Agulhasia King 1871
- Aidanosagitta Tokioka 1965
- Ailuropoda Milne-Edwards 1870
- Alactagulus Nehring 1897
- Alatocladia (Yendo) Johansen 1969
- Alcyna A. Adams 1860
- Alcyonidium Lamouroux 1813
- Aldingia Thomson 1916
- Alectis Rafinesque 1815
- Aleiodes Wesmael 1838
- Alepes Swainson 1839
- Alisometra A.H. Clark 1947
- Allactaga Cuvier 1836
- Allantus Panzer 1801
- Allium Linné 1753
- Allocricetulus Argyropulo 1932
- Allocyclops Kiefer 1932
- Allopeas H. B. Baker 1935
- Allorchestes Dana 1849
- Allotrochus Fagel 1955
- Alnus Miller 1754
- Alocasia (Schott) G.Don
- Aloe Linné
- Aloephagus Essig 1950
- Alpheus Fabricius 1798
- Alticola Blanford 1881
- Aluterus Cloquet 1816
- Alveopora de Blainville 1830
- Amara Bonelli 1810
- Amarsipus Haedrich 1969
- Amazona Lesson 1830
- Ambassis Cuvier & Valenciennes 1828
- Amblychaeturichthys Bleeker 1874
- Amblyeleotris Bleeker 1874
- Amblygobius Bleeker 1874
- Amblyomma Koch 1844
- Amblyopone Erichson 1842
- Amegilla Friese 1897
- Amia Linnaeus 1766
- Amidostomum Railliet & Henry 1909
- Amiota Loew 1862
- Ammobaculites Cushman 1910
- Ammodytes Linnaeus 1758
- Ammoglobigerina Eimer & Fickert 1899
- Ammonia Brünnich 1772
- Ammothea Leach 1814
- Ampelopsis Michaux
- Ampharete Malmgren 1866
- Amphibalanus Pitombo 2004
- Amphictene Savigny 1818
- Amphiops Erichson 1843
- Amphipholis Thomas 1966
- Amphiporus Ehrenberg 1831
- Amphiprion Bloch & Schneider 1801
- Ampithoe Stebbing 1899
- Amphithyris Thomson 1918
- Amusium Röding 1798
- Amynthas Kinberg 1867
- Anakinetica Richardson 1987
- Anapagurus Henderson 1886
- Anarhichas Linnaeus 1758
- Anatrichosoma Smith & Chitwood 1954
- Anax Leach 1815
- Anchialina Norman & Scott 1906
- Anchistrotos Tang & Izawa 2005
- Anchistus Borradaile 1898
- Ancistrum Maupas 1883
- Ancylostoma Dubini 1843
- Andrena Fabricius 1775
- Andrias Tschudi 1837
- Andricus Hartig 1840
- Androlaelaps Berlese 1903
- Anemone Linné
- Aneugmenus Hartig 1837
- Angaria Röding 1798
- Angiostrongylus Kamensky 1905
- Anguilla Garsault 1764
- Anguillicola Yamaguti 1935
- Anguillicoloides Moravec & Taraschewski 1988
- Angustassiminea Habe 1943
- Aniculus Dana 1852
- Anilocra Leach 1818
- Anisakis Dujardin 1845
- Anisodactylus Dejean 1829
- Anisolabis Fieber 1853
- Anisops Spinola 1837
- Annandaleum Newman & Ross 1971
- Anneissia Summers, Messing, Rouse 2014
- Anochetus Mayr 1861
- Anodonta Lamarck 1799
- Anolis Daudin 1802
- Anomalomyrma Taylor 1990
- Anopheles Meigen 1818
- Anoplius Dufour 1834
- Anoplogenius Chaudoir 1852
- Anoplolepis Santschi 1914
- Anotogaster Sélys 1854
- Antedon de Fréminville 1811
- Antennarius Lacépède 1798
- Anterhynchium de Saussure 1863
- Anthemiphyllia Pourtales 1878
- Anthenea Gray 1840
- Anthocidaris Lütken 1864
- Anthopleura Duchassaing de Fonbressin & Michelotti 1860
- Antimora Günther 1878
- Aonchotheca Lopez-Neyra 1947
- Aoroides Walker 1898
- Apatura Fabricius 1807
- Apenesia Westwood 1874
- Aphanoconia Wagner 1905
- Aphaenogaster Mayr 1853
- Aphelochaeta Blake 1991
- Aphelocheirus Westwood 1833
- Aphelonyx Mayr 1881
- Aphilaenus Vilbaste 1968
- Aphyocypris Günther 1868
- Apis Linnaeus 1758
- Apistus Cuvier 1829
- Aplidium Savigny 1816
- Aplysia Linnaeus 1767
- Apocryptodon Bleeker 1874
- Apocyclops Lindberg 1942
- Apodemus Kaup 1829
- Apogon Lacépède 1801
- Apogonichthyoides Smith 1949
- Apohyale Bousfield & Hendrycks 2002
- Apolygopsis Yasunaga, Schwartz & Chérot 2002
- Apolygus China 1941
- Apophua Morley 1913
- Apotomopterus Hope 1838
- Appasus Amyot & Serville 1843
- Apristus Chaudoir 1846
- Aproceros Malaise 1931
- Aquarius Schellenberg 1800
- Aquila Brisson 1760
- Arabella Grube 1850
- Arabidopsis Heynhold
- Arachis Linné
- Architeuthis Steenstrup in Harting 1860
- Araeosoma Mortensen 1903
- Araschnia Hübner 1819
- Arca Linnaeus 1758
- Arcania Learch 1817
- Archaeomysis Czerniavsky 1882
- Archaster Müller & Troschel 1840
- Archicolliuris Liebke 1931
- Archipatrobus Zamotajlov 1992
- Arcotheres Manning 1993
- Arctonoe Chamberlin 1920
- Arctoscopus Jordan & Evermann 1896
- Arctosia Cooper 1983
- Arcuatula Jousseaume in Lamy 1919
- Ardea Linnaeus 1758
- Ardisia W.T. Swingle 1788
- Arenicola Lamarck 1801
- Arenicolides Mesni 1898
- Arge Schrank 1802
- Argulus Müller 1785
- Argyreus Fabricius 1807
- Argyrosomus De la Pylaie 1835
- Argyrotheca Dall 1900
- Arianta Turton 1831
- Ariosoma Swainson 1838
- Arisaema C.F.P. von Martius 1831
- Aristaeomorpha Wood Mason 1891
- Aristeus Duvernoy 1840
- Aristichthys Oshima 1919
- Arius Cuvier & Valenciennes 1840
- Armandia Filippi 1861
- Armatocillenus Dupuis 1912
- Arostrilepis Mas-Coma & Tenora 1997
- Arothron Müller 1841
- Artemia Leach 1819
- Artemisia Linné 1753
- Arthrostoma Cameron 1927
- Arvicola Lacépède 1799
- Asaphidion Des Gozis 1886
- Asarum Linné 1753
- Ascaridia Dujardin 1845
- Ascaris Linnaeus 1758
- Ascarops van Beneden 1873
- Ascogaster Wesmael 1835
- Asellus Geoffroy 1762
- Aseraggodes Kaup 1858
- Asiagomphus Asahina 1985
- Aspasma D.S. Jordan & Fowler 1902
- Aspasmichthys Briggs 1955
- Aspicera Dahlbom 1842
- Aspiculuris Schulz 1924
- Aspidontus Cuvier 1835
- Assiminea Fleming 1828
- Astasia Dujardin 1841
- Aster Linné
- Asterina Nardo 1834
- Asterophila Randall & Heath 1912
- Asterropteryx Rüppell 1830
- Asthenosoma Grube 1867
- Astrabe D.S. Jordan & Snyder 1901
- Astrea Lamarck 1801
- Astreopora Blainville 1830
- Astroceramus Fisher 1906
- Astrocladus Verrill 1899
- Astropecten Gray 1840
- Astrosarkus Mah 2003
- Astrosclera Lister 1900
- Astrothauma Fisher 1913
- Ateles E. Geoffroy 1806
- Atelorias Fisher 1993
- Atergatis De Haan 1833
- Athalia Leach 1817
- Atherion D.S. Jordan & Starks 1901
- Atopocottus Bolin 1936
- Atorella Vanhöffen 1902
- Atrina Gray 1847
- Atrophaneura Reakirt 1865
- Attheyella Brady 1880
- Atule Jordan 1922
- Atyopsis Chace 1983
- Aucuba Thunberg
- Aulichthys Brevoort 1862
- Aulites Richardson 1987
- Aulocyathus Marenzeller 1904
- Aulonocarabus Reitter 1896
- Aulopus Cloquet 1816
- Auplopus Spinola 1841
- Austropeplea Cotton 1942
- Auxis Cuvier 1829
- Avicula Bruguière 1792
- Awaous Steindachner 1860
- Azygia Looss 1899