• Abiella chejagica Kanev, 1989 †: Roadian
• Abiella kolvae Kanev, 1983 †: Kungurian
• Abiella porochovskiensis Ragozin, 1938 †: Kungurian
• Abiella rotunda Ragozin, 1933 †: Cisuralian
• Abiella satura Kanev, 1994 †: Kungurian
• Abiella ussovi Ragozin, 1933 †: Guadalupian
• Abiella vana Kanev, 1994 †: Wordian
• Acanthoceramoporella granulosa (Ulrich, 1890) †: Ordovician
• Acanthoceramoporella triloba (Cumings & Galloway, 1913) †: Ordovician
• Acanthoceramoporella valliensis Karklins, 1984 †: Ordovician, Upper
• Acanthocidaris hastigera A. Agassiz & H.L. Clark, 1907: Cisuralian
• Acanthocladia biserialis Chronic, 1949 †: Paleozoic
• Acanthocladia crebriramosa Trizna, 1939 †: Permian
• Acanthocladia fruticosa Ulrich, 1890 †: Carboniferous
• Acanthocladia guadalupensis Girty, 1908 †: Guadalupian
• Acanthocladia macer Trizna, 1950 †: Sakmarian
• Acanthocladia multipora Fritz, 1932 †: Permian
• Acanthocladia pinnata Rogers, 1900 †: Carboniferous
• Acanthocladia rectangulata Xia & Liu, 1986 †: Carboniferous
• Acanthocladia robusta Yang & Lu, 1962 †: Permian
• Acanthocladia sparsifurcata Shulga-Nesterenko, 1941 †: Permian
• Acanthocladia striata Bolkhowitinova & Markoff, 1926 †: Carboniferous
• Acanthoclema alternatum (Hall, 1883) †: Emsian
• Acanthoclema asperum (Hall, 1852) †: Llandovery
• Acanthoclema distilum Bigey, 1988 †: Devonian, Middle
• Acanthoclema elegantula Ernst, 2008 †: Devonian, Middle
• Acanthoclema lineatum McNair, 1937 †: Devonian
• Acanthoclema parvula Ernst, Dorsch & Keller, 2011 †: Eifelian
• Acanthoclema triseriale (Hall, 1883) †: Emsian
• Acantholaminatus typicus Marintsch, 1998 †: Ordovician
• Acanthopecten latiplicatus Muromtseva & Turbanov, 1974 †: Tournaisian
• Acanthopecten tarchanensis Muromtseva & Turbanov, 1974 †: Tournaisian
• Acanthostictoporella angusta Ernst & Königshof, 2010 †: Givetian
• Acanthotrypa carnica Vinassa de Regny, 1915? †: Ordovician
• Actinodonta carinata Barrois, 1891 †: Floian
• Actinodonta cuneata Phillips, 1848 †: Llandovery
• Actinopteria epsilon J. Hall, 1883 †: Devonian, Upper
• Actinotrypa peculiaris (Rominger, 1866) †: Mississippian
• Acupipora mexicana Ernst & Vachard, 2017 †: Moscovian
• Adlatipora fossulata Gautier, Wyse Jackson & McKinney, 2013 †: Kungurian
• Admiratella improvida Gorjunova, 1992 †: Artinskian
• Aenigmoconcha elongata Benediktova, 1950 †: Cisuralian
• Aganaster cingulatus Easton, 1943 †: Carboniferous
• Aganaster gregarius (Meek & Worten, 1869) †: Devonian, Upper
• Aganaster huaanensis (Wu, 1980) †: Capitanian