• Abietinaria abietina (Linnaeus, 1758)
• Abietinaria filicula (Ellis & Solander, 1786)
• Abietinaria fusca (Johnston, 1847)
• Abietinaria interversa (Pictet & Bedot, 1900)
• Abietinaria pulchra (Nutting, 1904)
• Abylopsis eschscholtzii (Huxley, 1859)
• Abylopsis tetragona (Otto, 1823)
• Abyssopathes lyra (Brook, 1889)
• Acanella arbuscula (Johnson, 1862)
• Acanthogorgia armata Verrill, 1878
• Acanthogorgia hirsuta Gray, 1857
• Acanthogorgia pico Grasshoff, 1973
• Acaulis primarius Stimpson, 1853
• Acauloides ammisatum Bouillon, 1965
• Acauloides ilonae (Brinckmann-Voss, 1966)
• Acryptolaria conferta (Allman, 1877)
• Acryptolaria crassicaulis (Allman, 1888)
• Acryptolaria longitheca (Allman, 1877)
• Acthelmis intestinalis (Fabricius, 1780)
• Acthelmis schaudinnii Carlgren, 1921 accepted as Haliactis arctica Carlgren, 1921
• Actigia vanbenedeni (Hincks, 1869) accepted as Coryne vanbenedenii Hincks, 1868
• Actinauge abyssorum (Gravier, 1918) accepted as Actinauge karinae Fautin, 2016
• Actinauge abyssorum Carlgren, 1934
• Actinauge karinae Fautin, 2016
• Actinauge richardi (Marion, 1906)
• Actinernus michaelsarsi Carlgren, 1918
• Actinia candida Müller, 1776 accepted as Metridium senile (Linnaeus, 1761)
• Actinia cari Delle Chiaje, 1822
• Actinia elongata Delle Chiaje, 1825 (unaccepted)
• Actinia equina (Linnaeus, 1758)
• Actinia equina mediterranea Schmidt, 1971 accepted as Actinia mediterranea Schmidt, 1971
• Actinia filiformis Rapp, 1829 accepted as Cereus filiformis (Rapp, 1829)
• Actinia fragacea Tugwell, 1856
• Actinia mediterranea Schmidt, 1971
• Actinia prasina Gosse, 1860
• Actinia sali Monteiro, Sole-Cava & Thorpe, 1997
• Actinia schmidti Monteiro, Sole-Cava & Thorpe, 1997 accepted as Actinia mediterranea Schmidt, 1971
• Actinia striata Quoy & Gaimard, 1833
• Actinia striata Rizzi, 1907 (accepted > unreplaced junior homonym)
• Actinoscyphia aurelia (Stephenson, 1918)
• Actinoscyphia saginata (Verrill, 1882)
• Actinostola abyssorum (Danielssen, 1890)
• Actinostola callosa (Verrill, 1882)
• Actinothoe clavata (Ilmoni, 1830) accepted as Sagartiogeton undatus (Müller, 1778) accepted as Cylista undata (Müller, 1778) accepted as Sagartia undata (Müller, 1778)
• Actinothoe sphyrodeta (Gosse, 1858)
• Adamsia carciniopados (Otto, 1823) accepted as Adamsia palliata (Fabricius, 1779) accepted as Calliactis palliata (Müller, 1776)
• Adamsia palliata (Bohadsch, 1761) accepted as Adamsia palliata (Fabricius, 1779) accepted as Calliactis palliata (Müller, 1776)
• Adamsia palliata (Fabricius, 1779) accepted as Calliactis palliata (Müller, 1776)
• Aegina citrea Eschscholtz, 1829
• Aegina rosea Eschscholtz, 1829
• Aeginopsis laurentii Brandt, 1838
• Aeginura grimaldii Maas, 1904
• Aequorea aequorea (Forsskål, 1775) accepted as Aequorea forskalea Péron & Lesueur, 1810
• Aequorea conica Browne, 1905
• Aequorea forskalea Péron & Lesueur, 1810
• Aequorea macrodactyla (Brandt, 1835)
• Aequorea pensilis (Haeckel, 1879)
• Aequorea vitrina Gosse, 1853
• Agalma clausi Bedot, 1888
• Agalma elegans (M. Sars, 1846)
• Agalma okenii Eschscholtz, 1825
• Agalma rubra Vogt, 1852 accepted as Halistemma rubrum (Vogt, 1852)
• Agalmopsis utricularia Claus, 1879 accepted as Lychnagalma utricularia (Claus, 1879)
• Aglantha digitale (O. F. Müller, 1776)
• Aglantha elata (Haeckel, 1879)
• Aglaophenia acacia Allman, 1883
• Aglaophenia elongata Meneghini, 1845
• Aglaophenia harpago Schenck, 1965
• Aglaophenia kirchenpaueri (Heller, 1868)
• Aglaophenia latecarinata Allman, 1877
• Aglaophenia lophocarpa Allman, 1877
• Aglaophenia octodonta (Heller, 1868)
• Aglaophenia parvula Bale, 1882
• Aglaophenia picardi Svoboda, 1979
• Aglaophenia pluma (Linnaeus, 1758)
• Aglaophenia tubiformis Marktanner-Turneretscher, 1890
• Aglaophenia tubulifera (Hincks, 1861)
• Aglaophenopsis bonnevieae (Jäderholm, 1909)
• Aglaophenopsis cartieri (Bedot, 1921)
• Aglaophenopsis cornuta (Fewkes, 1881)
• Aglaura hemistoma Péron & Lesueur, 1810
• Aiptasia couchii Gosse
• Aiptasia diaphana (Rapp, 1829) accepted as Exaiptasia diaphana (Rapp, 1829)
• Aiptasia mutabilis (Gravenhorst, 1831)
• Aiptasiogeton hyalinus (Delle Chiaje, 1822)
• Aiptasiogeton pellucidus (Hollard, 1848) accepted as Aiptasiogeton hyalinus (Delle Chiaje, 1822)
• Alataspora africana Schulman, Kovaleva & Dubina, 1979
• Alataspora caproi Gaevskaja & Kovaleva, 1984
• Alataspora contrariocapsularia Schulman, Kovaleva & Dubina, 1979
• Alataspora lepidum Gaevskaya & Kovaljova, 1979
• Alataspora serenum Gaevskaja & Kovaleva, 1979
• Alataspora solomoni Yurakhno, 1988
• Alataspora tetricum Gaevskaya & Kovaljova, 1979
• Alcyonium acaule Marion, 1878
• Alcyonium aurantium Pallas, 1766 accepted as Tethya aurantium (Pallas, 1766)
• Alcyonium bocagei (Saville Kent, 1870)
• Alcyonium boletiforme Lamarck, 1815 accepted as Polymastia boletiformis (Lamarck, 1815)
• Alcyonium coralloides (Pallas, 1766)
• Alcyonium cranium Müller, 1776 accepted as Craniella cranium (Müller, 1776)
• Alcyonium cydonium Linnaeus, 1767 accepted as Geodia cydonium (Linnaeus, 1767)