• "Merodermid clade" (temporary name)
• [BETA] prion
• [Het-s] prion
• [PIN] prion
• [PSI] prion
• [URE3] prion
• Aa Baker, 1940 accepted as Philonesia Sykes, 1900 [Family: Helicarionidae]
• Aa H.G. Reichenbach, 1854 [Family: Orchidaceae]
• Aaaba Bellamy, 2002 [Family: Buprestidae]
• Aaaba de Laubenfels, 1936 accepted as Crellastrina Topsent, 1927 [Family: Crellidae]
• Aaaba fossicollis (Kerremans, 1903)
• Aaaba nodosus (Deyrolle, 1865)
• Aaadonta Solem, 1976
• Aaages Barovskiĭ, 1926
• Aaata de Laubenfels, 1930 accepted as Clathria Schmidt, 1862 [Family: Microcionidae]
• Aaata Semenov, 1906 [Family: Buprestidae]
• Aaata brepha de Laubenfels, 1930 accepted as Clathria brepha (de Laubenfels, 1930)
• Aaata spongigartina de Laubenfels, 1930 accepted as Clathria spongigartina (de Laubenfels, 1930)
• Aaba de Laubenfels, 1936 accepted as Crellastrina Topsent, 1927
• Aabacharis Schauff, 1991 accepted as Eprhopalotus Girault, 1916
• Aacanthocnema Tuthill & Taylor, 1955
• Aacanthocnema banksiae (Froggatt, 1901)
• Aacanthocnema casuarinae (Froggatt, 1901)
• Aacanthocnema dobsoni (Froggatt, 1903)
• Aachenaspis Egerton, 1857 † accepted as Auchenaspis Egerton, 1857 †
• Aachenia E. Knobloch, 1972 †
• Aachenipollis W. Krutzsch, 1970 †
• Aachenosaurus Smets, 1887 † accepted as Aachenoxylon M. Hovelacque, 1889 †
• Aachenoxylon M. Hovelacque, 1889 †
• Aachnoideus Chaudoir, 1838 accepted as Pterostichus Bonelli, 1810
• Aackia Yosii, 1966
• Aacocrinus Bowsher, 1955 †
• Aades Schönherr, 1823
• Aafrita Szwedo & Azar in Szwedo, Azar & Nohra, 2013 †
• Aagaardia Sæther, 2000
• Aagaardia longicalcis Sæther, 2000
• Aagaardia protensa Sæther, 2000
• Aagaardia triangulata Sæther, 2000
• Aageocolletes Engel, 2022
• Aages Barovskiĭ, 1926 accepted as Aaages Barovskiĭ, 1926
• Aages prior Barovskij, 1926
• Aaglacrinus † accepted as Aglaocrinus Strimple, 1961 †
• Aaglaocrinus Webster, 1981 † (uncertain)
• Aagyrus accepted as Anagyrus Howard, 1896
• Aagyrus chrysos Noyes & Hayat, 1994 accepted as Anagyrus chrysos Noyes & Hayat, 1994
• Aahithis Schallreuter, 1988 †
• Aaka Dworakowska, 1972 (uncertain)
• Aakia J.R. Grande, 2014 accepted as Panicum Linnaeus, 1753
• Aalatettix Zheng & Mao, 2002
• Aalatettix longipulvillus Zheng & Mao, 2002
• Aaleniella Conti & Fischer, 1981 † [Family: Trochidae]
• Aaleniella Plumhoff, 1963 † [Family: Eucytheridae]
• Aalenilla Phemhoff, 1963 † accepted as Aaleniella Plumhoff, 1963 †
• Aalenirhynchia Shi & Grant, 1993 †
• Aalinga Viraktamath & Webb, 2019
• Aalius Rumphius ex O. Kuntze, 1891 accepted as Sauropus Blume, 1826
• Aalius androgyna (L.) Kuntze accepted as Sauropus androgynus (L.) Merr.
• Aalius assimilis (Thwaites) Kuntze accepted as Sauropus assimilis Thwaites
• Aalius brevipes (Müll. Arg.) Kuntze accepted as Sauropus brevipes Müll. Arg.
• Aalius ceratogynum Kuntze accepted as Sauropus quadrangularis (Willd.) Müll. Arg.
• Aalius compressa (Müll. Arg.) Kuntze accepted as Sauropus quadrangularis (Willd.) Müll. Arg.
• Aalius forcipata (Hook. f.) Kuntze accepted as Sauropus macranthus Hassk.
• Aalius lanceolata (Hook. f.) Kuntze accepted as Sauropus rhamnoides Blume
• Aalius macrantha (Hassk.) Kuntze accepted as Sauropus macranthus Hassk.
• Aalius macrophylla (Hook. f.) Kuntze accepted as Sauropus macranthus Hassk.
• Aalius oblongifolia (Hook. f.) Kuntze accepted as Sauropus oblongifolius Hook. f.
• Aalius pubescens (Hook. f.) Kuntze accepted as Sauropus quadrangularis (Willd.) Müll. Arg.
• Aalius quadrangularis (Müll. Arg.) Kuntze accepted as Sauropus quadrangularis (Willd.) Müll. Arg.
• Aalius retroversa (Wight) Kuntze accepted as Sauropus androgynus (L.) Merr.
• Aalius rhamnodes (Blume) Kuntze accepted as Sauropus rhamnoides Blume
• Aalius rigida (Thwaites) Kuntze
• Aalius rostrata (Miq.) Kuntze accepted as Sauropus rostratus Miq.
• Aalius spectabilis (Miq.) Kuntze accepted as Sauropus macranthus Hassk.
• Aalius stipitata (Hook. f.) Kuntze accepted as Sauropus stipitatus Hook. f.
• Aalius sumatrana (Miq.) Kuntze accepted as Sauropus androgynus (L.) Merr.
• Aalius trinervia (Hook. f. & Thomson ex Müll. Arg.) Kuntze accepted as Sauropus trinervius Hook. f. & Thomson ex Müll. Arg.
• Aalivirus
• Aalolana accepted as Aatolana Bruce, 1993
• Aalolana rapax Bruce, 1993 (unaccepted)
• Aamunops Galán-Sánchez & Álvarez-Padilla, 2022
• Aancistroger Bei-Bienko, 1957
• Aancistroger sinicus Bei-Bienko, 1957
• Aaosphaeria A. Aptroot, 1995
• Aaosphaeria arxii (Aa) Aptroot, 1995
• Aapticheilichthys Huber, 2011
• Aaptochiton Hoare & Karasawa, 2008 †
• Aaptolasma Newman & Ross, 1971 accepted as Hexelasma Hoek, 1913
• Aaptolasma americana (Pilsbry, 1916)
• Aaptolasma brintoni Newman & Ross, 1971
• Aaptolasma callistoderma (Pilsbry, 1911)
• Aaptolasma fosteri (Newman & Ross, 1971)
• Aaptolasma leptoderma Newman & Ross, 1971
• Aaptolasma nolearia Foster, 1978
• Aaptolasma triderma Newman & Ross, 1971
• Aaptoryctes Gingerich, 1982 †
• Aaptos Gray, 1867
• Aaptos aaptos (Schmidt, 1864)
• Aaptos adriatica Gray, 1867 accepted as Aaptos aaptos (Schmidt, 1864)
• Aaptos alphiensis Samaai & Gibbons, 2005
• Aaptos bergmanni de Laubenfels, 1950