• Abditodentrix pseudothalmanni (Boltovskoy & Guissani de Kahn, 1981): Miocene
• Abertella kewi Durham, 1957 †: Miocene
• Abertella palmeri Durham, 1957 †: Miocene
• Abra cytheraeformis Cossmann & Peyrot, 1909 †: Aquitanian
• Abra fragosa (Marwick, 1931) †: Miocene
• Abra marshalli (H. J. Finlay, 1927) †: Miocene
• Acanthinula hesslerana Jooss, 1911 †: Aquitanian
• Acanthocardia allae Studencka & Popov, 1996 †: Miocene
• Acanthocardia andreae (Dujardin, 1837) †: Miocene
• Acanthocardia otarii (Kharatishvili, 1952) †: Miocene
• Acasta schafferi de Alessandri, 1910 †: Miocene
• Acharax gigas (Kanno, 1960) †: Miocene
• Acharax muroensis (Natori, 1964) †: Aquitanian
• Acicula limbata Reuss, 1861 †: Burdigalian
• Acila antefultoni Slodkevich, 1967 †: Miocene
• Acila perfecta Slodkevich, 1967 †: Miocene
• Acirsa awamoaensis (P. Marshall & Murdoch, 1921) †: Miocene
• Acirsa subnodulosa (P. A. Maxwell, 1988) †: Miocene
• Aclis ascaris (W. Turton, 1819): Tortonian
• Acroloxus anatolicus Schütt, 1984 †: Langhian
• Acroloxus ucrainicus Gozhik & Prysjazhnjuk, 1978 †: Tortonian
• Acrosterigma fraternum (Mayer, 1864) †: Burdigalian
• Acrosterigma fraternum (Mayer, 1864) †: Aquitanian
• Actapericulum bicarinatum Holmes, 1995 †: Langhian
• Actapericulum bicarinatum Holmes, 1995 †: Burdigalian
• Acteocina kirkwoodiana H. G. Richards & Harbison, 1944 †: Miocene
• Acteon chilensis R. A. Philippi, 1887 †: Burdigalian
• Acteon infulatus Marwick, 1931 †: Miocene
• Acteon otamateaensis Laws, 1941 †: Miocene
• Actinobalanus bisculcatus (Darwin, 1854): Burdigalian
• Actinobalanus dolosus (Darwin, 1854) †: Miocene
• Actinobalanus inclusus (Darwin, 1854): Miocene
• Actinobalanus stellaris (Brocchi, 1814) †: Miocene
• Actinopora plicata Canu, 1916 †: Burdigalian
• Acuticosta baicalica B.-Y. Huang, 1964 †: Miocene
• Adenifera striata (MacGillivray, 1895) †: Miocene
• Adeona interdigitata MacGillivray, 1895 †: Miocene
• Adeonellopsis deformis (Canu & Bassler, 1919) †: Miocene
• Adeonellopsis glenaulinensis Brown, 1958 †: Miocene
• Adeonellopsis maghrebensis El Hajjaji, 1992 †: Messinian
• Adeonellopsis sandbergi Di Martino, Taylor & Portell, 2017 †: Burdigalian
• Admetula serrata (Bronn, 1831) †: Tortonian
• Admetula serrata (Bronn, 1831) †: Serravallian
• Admetula serrata (Bronn, 1831) †: Langhian
• Aechmella ambigua (MacGillivray, 1895) †: Miocene
• Aechmella depressa (MacGillivray, 1895) †: Miocene
• Aechmella poluzzii Moissette, 1988 †: Miocene
• Aechmella rakhamensis Abbas & El-Senoussi, 1979 †: Miocene
• Aetea truncata (Landsborough, 1852): Miocene
• Afripupa kenyensis Pickford, 2019 †: Burdigalian
• Agaronia gibbosa (Born, 1778): Serravallian
• Agaronia ispidula (Linnaeus, 1758) †: Miocene
• Agassizia (Agassizia) powersi Kier, 1972a †: Miocene
• Agassizia algarbiensis Da Veiga Ferreira, 1962 †: Miocene