Abietinaria abietina (Linnaeus, 1758) (additional source)
Acanthodoris pilosa (Abildgaard, 1789) (additional source)
Acarina accepted as Acari (basis of record)
Acasta Leach, 1817 (additional source)
Acasta spongites (Poli, 1791) (additional source)
Actacarus Schulz, 1937 (additional source)
Actinia equina (Linnaeus, 1758) (additional source)
Actinia fragacea Tugwell, 1856 (additional source)
Actiniaria (basis of record)
Actiniidae Rafinesque, 1815 (additional source)
Actinostolidae Carlgren, 1932 (additional source)
Actinothoe Fischer, 1889 (additional source)
Actinothoe sphyrodeta (Gosse, 1858) (additional source)
Adalaria proxima (Alder & Hancock, 1854) (additional source)
Adamsia Forbes, 1840 accepted as Calliactis Verrill, 1869 (additional source)
Aeginina longicornis (Krøyer, 1843) (additional source)
Aeolidiella alderi (Cocks, 1852) (additional source)
Aeolidiella glauca (Alder & Hancock, 1845) (additional source)
Aepophilus Signoret, 1879 (additional source)
Aepophilus bonnairei Signoret, 1879 (additional source)
Aepopsis Jeannel, 1922 (additional source)
Aepopsis robinii (Laboulbene, 1849) (additional source)
Aepus Leach in Samouelle, 1819 (additional source)
Aepus marinus (Stroem, 1788) (additional source)
Aetea anguina (Linnaeus, 1758) (additional source)
Aetea sica (Couch, 1844) (additional source)
Aetea truncata (Landsborough, 1852) (additional source)
Agabus Leach, 1817 (basis of record)
Agabus conspersus (Marsham) (basis of record)
Agauopsis Viets, 1927 (additional source)
Aglaophenia acacia Allman, 1883 (additional source)
Aglaophenia kirchenpaueri (Heller, 1868) (additional source)
Aglaophenia tubulifera (Hincks, 1861) (additional source)
Aiptasia Gosse, 1858 (additional source)
Aiptasia mutabilis (Gravenhorst, 1831) (additional source)
Aiptasiidae Carlgren, 1924 (additional source)
Alcyonacea accepted as Octocorallia (basis of record)
Alcyonidium Lamouroux, 1813 (additional source)
Alcyonidium gelatinosum (Linnaeus, 1761) (additional source)
Alcyonidium hirsutum (Fleming, 1828) (additional source)
Alcyonidium parasiticum (Fleming, 1828) (additional source)
Alcyoniidae Lamouroux, 1812 (additional source)
Alcyonium digitatum Linnaeus, 1758 (additional source)
Alcyonium glomeratum (Hassall, 1843) (additional source)
Alderia modesta (Lovén, 1844) (additional source)
Aleochara Gravenhorst, 1802 (basis of record)
Allomelita pellucida (G.O. Sars, 1883) (additional source)
Alloteuthis media (Linnaeus, 1758) (additional source)
Alloteuthis subulata (Lamarck, 1798) (additional source)
Alpheus Fabricius, 1798 (additional source)
Amalosoma Fisher, 1948 (additional source)
Amalosoma eddystonense Stephen, 1956 (additional source)
Amathia Lamouroux, 1812 (additional source)
Amathia lendigera (Linnaeus, 1758) (additional source)
Amblyosyllis formosa (Claparède, 1863) accepted as Amblyosyllis spectabilis (Johnston in Baird, 1861) (additional source)
Ammotheidae Dohrn, 1881 (basis of record)
Amoebidae Ehrenberg, 1838 (basis of record)
Amphiblestrum Gray, 1848 (additional source)
Amphiblestrum flemingii (Busk, 1854) (additional source)
Amphichaeta Tauber, 1879 (additional source)
Amphichaeta sannio Kallstenius, 1892 (additional source)
Amphiglena mediterranea (Leydig, 1851) (additional source)
Amphilectus Vosmaer, 1880 (additional source)
Amphilectus fucorum (Esper, 1794) (additional source)
Amphiporidae Örsted, 1843 (additional source)
Amphiporus Ehrenberg, 1831 (additional source)
Amphiporus allucens Bürger, 1895 (additional source)
Amphiporus bioculatus sensu Verrill, 1892 (additional source)
Amphiporus dissimulans Riches, 1893 (additional source)
Amphiporus elongatus Stephenson, 1911 accepted as Psammamphiporus elongatus (Stephenson, 1911) (basis of record)
Amphiporus hastatus McIntosh, 1874 (additional source)
Amphiporus lactifloreus (Johnston, 1828) (additional source)
Amphitholina cuniculus (Stebbing, 1874) (additional source)
Amphitritides gracilis (Grube, 1860) (additional source)
Ampithoe gammaroides (Spence Bate, 1857) accepted as Pleonexes gammaroides Spence Bate, 1857 (additional source)
Ampithoe helleri Karaman, 1975 accepted as Pleonexes helleri (Karaman, 1975) (additional source)
Anapagurus chiroacanthus (Liljeborg, 1856) (additional source)
Anasca accepted as Flustrina (basis of record)
Anchialina agilis (G.O. Sars, 1877) (additional source)
Anchinoe Gray, 1867 accepted as Phorbas Duchassaing & Michelotti, 1864 (additional source)
Anchinoe fictitius (Bowerbank, 1866) accepted as Phorbas fictitius (Bowerbank, 1866) (additional source)
Ancyroniscus Caullery & Mesnil, 1919 (basis of record)
Ancyroniscus bonnieri Caullery & Mesnil, 1919 (basis of record)
Anemonia Risso, 1827 (additional source)
Anemonia viridis (Forsskål, 1775) (additional source)
Anguilla anguilla (Linnaeus, 1758) (additional source)
Anguinella van Beneden, 1845 (additional source)
Angulus squalidus (Pulteney, 1799) accepted as Tellina incarnata Linnaeus, 1758 accepted as Bosemprella incarnata (Linnaeus, 1758) (basis of record)
Annectocyma Hayward & Ryland, 1985 (additional source)
Annectocyma major (Johnston, 1847) (additional source)
Annelida (additional source)
Anopla accepted as Nemertea incertae sedis (basis of record)
Antalis entalis (Linnaeus, 1758) (basis of record)
Antalis vulgare (da Costa, 1778) accepted as Antalis vulgaris (da Costa, 1778) (basis of record)
Antennella Allman, 1877 (additional source)
Antho involvens (Schmidt, 1864) represented as Antho (Antho) involvens (Schmidt, 1864) (additional source)
Anthopleura Duchassaing de Fonbressin & Michelotti, 1860 (additional source)
Anthopleura ballii (Cocks, 1851) (additional source)
Anthopleura thallia (Gosse, 1854) (additional source)
Anurida Laboulbène, 1865 (additional source)

British Isles for Hermaea bifida (Montagu, 1816) 
British Isles for Laevicardium crassum (Gmelin, 1791) 
British Isles for Tellimya ferruginosa (Montagu, 1808) 
East Coast of Scotland for Hermaea bifida (Montagu, 1816) 
English Channel for Hippolyte longirostris (Czerniavsky, 1868) 
English Channel for Ocinebrina aciculata (Lamarck, 1822) 
Scilly Isles for Ocinebrina aciculata (Lamarck, 1822) 
South Coast of England for Liocarcinus arcuatus (Leach, 1814) 
South Coast of Ireland for Emarginula crassa J. Sowerby, 1813 
West Coast of England for Liocarcinus arcuatus (Leach, 1814) 
West Coast of Ireland for Hermaea bifida (Montagu, 1816) 

English coalfish for Pollachius virens (Linnaeus, 1758)
English coley for Pollachius virens (Linnaeus, 1758)
English common dragonet for Callionymus lyra Linnaeus, 1758
English Connemara clingfish [from synonym] for Lepadogaster candollei Risso, 1810
English Corbin's sand eel for Hyperoplus immaculatus (Corbin, 1950)
English corkwing [from synonym] for Symphodus (Crenilabrus) melops (Linnaeus, 1758)
English Cornish clingfish [from synonym] for Lepadogaster lepadogaster purpurea (Bonnaterre, 1788)
English deep-nosed pipefish for Syngnathus typhle Linnaeus, 1758
English father lasher for Myoxocephalus scorpius (Linnaeus, 1758)
English fluke for Platichthys flesus (Linnaeus, 1758)
English John dory for Zeus faber Linnaeus, 1758
English lamprey for Lampetra fluviatilis (Linnaeus, 1758)
English lesser pipefish for Syngnathus rostellatus Nilsson, 1855
English lesser sand eel for Ammodytes tobianus Linnaeus, 1758
English painted ray for Raja microocellata Montagu, 1818
English poor-cod for Trisopterus minutus (Linnaeus, 1758)
English pout for Trisopterus luscus (Linnaeus, 1758)
English Raitt's sand eel for Ammodytes marinus Raitt, 1934
English reticulate dragonet for Callionymus reticulatus Valenciennes, 1837
English sand smelt [from synonym] for Atherina (Hepsetia) presbyter Cuvier, 1829
English sapphirine gurnard [from synonym] for Trigla lucerna Linnaeus, 1758
English sea snail for Liparis liparis (Linnaeus, 1766)
English streaked gurnard [from synonym] for Trigloporus lastoviza (Bonnaterre, 1788)
English trout for Salmo trutta Linnaeus, 1758
English tub [from synonym] for Trigla lucerna Linnaeus, 1758
English turbot [from synonym] for Psetta maxima (Linnaeus, 1758)
English two spot goby [from synonym] for Gobiusculus flavescens (Fabricius, 1779)