Abylidae, Familia
Abylopsinae, Subfamilia
Acanthephyra, Genus
Acanthomysis, Genus
Acotylea, Subordo
Acrania, Subphylum
– synonym of Cephalochordata, Subphylum
Acrania | Bleeker, 1859, Subphylum
– synonym of Cephalochordata, Subphylum
Actinotrocha, Genus
Aegidae, Familia
Aequorea, Genus
Aequoreidae, Familia
Agalma, Genus
Agalmatidae, Familia
Aglantha, Genus
Alaurina, Genus
Alciopa, Genus
Alciopidae, Familia
Alloposidae, Familia
Alloteuthis, Genus
Alpheidae, Familia
Alpheoidea, Superfamilia
Amblyops, Genus
Amphinema, Genus
Amphipoda, Ordo
Anchialina, Genus
Animalia, Regnum
Annelida, Phylum
Anomura, Infraorder
Anthoathecatae, Subclassis
Anthozoa, Superclass
Apolemia, Genus
Apolemiidae, Familia
Appendicularia, Classis
Appendicularia, Genus
Arachnactidae, Familia
Arachnactis, Genus
Architeuthidae, Familia
Architeuthis, Genus
Arthropoda, Phylum
Ascidiacea, Classis
Asellota, Subordo
Astacidea, Infraorder
Asterias, Genus
Asteriidae, Familia
Asteroidea, Classis
Asterope, Genus
Asterozoa, Subphylum
Athanas, Genus
Atolla, Genus
Atollidae, Familia
Atyoidea, Superfamilia
Aurelia, Genus