1. Acanthasteridae Sladen 1889
2. Acanthinulidae Steenberg 1917
3. Acanthochitonidae Pilsbry 1893
4. Acanthuridae Bonaparte 1832
5. Accipitridae Vieillot 1816
6. Acipenseridae Bonaparte 1831
7. Acoraceae Linné 1753
8. Acrididae MacLeay 1819
9. Acrocephalidae Alström et al. 2006
10. Acrocirridae Banse 1969
11. Acropomatidae T.N. Gill 1893
12. Acroporidae Verrill 1902
13. Acteonidae d'Orbigny 1843
14. Actiniidae Rafinesque 1815
15. Acuariidae Railliet, Henry & Sisoff 1912
16. Adiantaceae
17. Adoxaceae E. Meyer 1839
18. Adrianichthyidae M.C.W. Weber 1913
19. Aegisthidae Giesbrecht 1893
20. Aeschnidae Rambur 1842
21. Agamidae Gray 1827
22. Agariciidae Gray 1847
23. Agelasidae Verrill 1907
24. Aizoaceae Martynov
25. Alariaceae Setchell & Gardner 1925
26. Alaudidae Vigors 1825
27. Alcyonidiidae Johnston 1838
28. Aleyrodidae
29. Allocreadiidae Looss 1902
30. Alpheidae Rafinesque 1815
31. Alydidae Amyot & Serville 1843
32. Amaranthaceae de Jussieu 1789
33. Amarsipidae Haedrich 1969
34. Amaryllidaceae J. St.-Hilaire 1805
35. Ambassidae Klunzinger 1870
36. Amblycipitidae F. Day 1873
37. Ameiridae Boeck 1865
38. Amiidae Bonaparte 1838
39. Ammodytidae Bonaparte 1835
40. Ammotheidae Dohrn 1881
41. Ampharetidae Malmgren 1866
42. Amphinomidae Savigny in Lamarck 1818
43. Amphiporidae McIntosh 1874
44. Amphiuridae Ljungman 1867
45. Ampithoidae Stebbing 1899
46. Ampullariidae J.E. Gray 1824
47. Anacardiaceae R.Brown 1818
48. Anarhichadidae Bonaparte 1835
49. Ancistridae Issel 1903
50. Ancylostomatidae Looss 1905
51. Ancyrocephalidae Bychowsky & Nagibina 1968
52. Andrenidae
53. Angariidae Gray 1857
54. Anguillicolidae Yamaguti 1935
55. Angullidae Rafinesque 1810
56. Anisakidae Skrjabin & Karokhin 1945
57. Anisogammaridae Bousfield 1977
58. Anisolabididae Verhoeff 1902
59. Anoplocephalidae Cholodkovsky 1902
60. Antedonidae Norman 1865
61. Antennariidae T.N. Gill 1863
62. Anthemiphyllidae Vaughan 1907
63. Anthuridae Leach 1814
64. Aoridae Walker 1908
65. Aphelochiridae
66. Aphididae Latreille 1802
67. Aphrophoridae Evans 1946
68. Apidae
69. Apistidae Gill 1859
70. Aploactinidae McCulloch 1922
71. Aplysiidae Lamarck 1809
72. Apogonidae Günther 1859
73. Aquifoliaceae de Candolle ex A. Richard 1830
74. Arabellidae Hartman 1944
75. Araceae de Jussieu 1789
76. Araliaceae de Jussieu 1789
77. Arbaciidae Gray 1855
78. Archaeobalanidae Newman & Ross 1976
79. Archasteridae Viguier 1878
80. Architeuthidae Pfeffer 1900
81. Arcidae Lamarck 1809
82. Ardeidae Leach 1820
83. Arecaceae von Berchtold & J. Presl 1820
84. Arenicolidae Johnston 1835
85. Argidae Konow 1890
86. Argulidae Leach 1819
87. Ariidae L.S. Berg 1958
88. Aristeidae Wood-Mason
89. Aristolochiaceae de Jussieu 1789
90. Artemiidae Grochowski 1895
91. Ascarididae Baird 1853
92. Ascaridiidae Travassos 1919
93. Ascorhynchidae Hoek 1881
94. Asellidae Latreille 1802
95. Asilidae Friedrich 1873
96. Assimineidae H. Adams & A. Adams 1856
97. Asteraceae von Berchtold & J. Presl 1820
98. Asteriidae Gray 1840
99. Asterinidae Gray 1840
100. Asterocheridae Giesbrecht 1899
101. Astrocoeniidae Koby 1890
102. Astropectinidae Gray 1840
103. Astroscleridae Lister 1900
104. Atelidae Gray 1825
105. Atherinidae Risso 1827
106. Atorellidae Vanhöffen 1902
107. Atractidae Travassos 1919
108. Atyidae De Haan 1849
109. Aulacidae Shuckard 1841
110. Aulopidae Cope 1872
111. Azygiidae Lühe 1909