| Order | Family | Species | Occurrence | SeaLifeBase name | Name |
|---|---|---|---|---|---|
| Rotaliida | Amphisteginidae | Amphistegina lessonii | native | ||
| Littorinimorpha | Anabathridae | Amphithalamus rauli | native | ||
| Littorinimorpha | Anabathridae | Amphithalamus vallei | native | Del Valle's tiny shell | |
| Amphilepidida | Amphiuridae | Amphiura fibulata | native | ||
| Amphilepidida | Amphiuridae | Amphiura stimpsoni | native | ||
| Trachymedusae | Rhopalonematidae | Amphogona apsteini | native | ||
| Amphipoda | Ampithoidae | Ampithoe marcuzzii | native | ||
| Pectinida | Pectinidae | Amusium papyraceum | native | Paper scallop | |
| Arcida | Arcidae | Anadara notabilis | native | Eared ark | |
| Cladophorales | Anadyomenaceae | Anadyomene saldanhae | native | ||
| Cladophorales | Anadyomenaceae | Anadyomene stellata | native | Papyrus print alga | |
| Comatulida | Colobometridae | Analcidometra armata | native | Swimming sea lily | |
| Amphipoda | Leucothoidae | Anamixis hanseni | native | ||
| Amphipoda | Leucothoidae | Anamixis vanga | native | ||
| Sabellida | Sabellidae | Anamobaea orstedii | native | Split-crown feather duster | Split-crown feather duster |
| Isopoda | Ancinidae | Ancinus belizensis | native | ||
| Oegopsida | Ancistrocheiridae | Ancistrocheirus lesueurii | native | Sharpear enope squid | |
| Decapoda | Palaemonidae | Ancylomenes pedersoni | native | Pederson cleaner shrimp | Pederson cleaner shrimp |
| Isopoda | Microparasellidae | Angeliera psamathus | native | ||
| Not assigned | Planaxidae | Angiola lineata | native | Dwarf Atlantic planaxis | |
| Isopoda | Microparasellidae | Angliera psamathus | native | ||
| Cardiida | Tellinidae | Angulus merus | native | ||
| Cardiida | Tellinidae | Angulus probinus | native | ||
| Cardiida | Tellinidae | Angulus versicolor | native | Many-colored tellin | |
| Lucinida | Lucinidae | Anodontia schrammi | native | ||
| Venerida | Veneridae | Anomalocardia auberiana | native | Pointed venus | |
| Venerida | Veneridae | Anomalocardia brasiliana | native | West Indian pointed venus | |
| Pectinida | Anomiidae | Anomia ephippium | native | Common jingle shell | |
| Pantopoda | Phoxichilidiidae | Anoplodactylus bahamensis | native | ||
| Pantopoda | Phoxichilidiidae | Anoplodactylus batangensis | native | ||
| Pantopoda | Phoxichilidiidae | Anoplodactylus californicus | native | ||
| Pantopoda | Phoxichilidiidae | Anoplodactylus evelinae | native | ||
| Pantopoda | Phoxichilidiidae | Anoplodactylus imswe | native | ||
| Pantopoda | Phoxichilidiidae | Anoplodactylus jonesi | native | ||
| Pantopoda | Phoxichilidiidae | Anoplodactylus maritimus | native | ||
| Pantopoda | Phoxichilidiidae | Anoplodactylus monotrema | native | ||
| Pantopoda | Phoxichilidiidae | Anoplodactylus multiclavus | native | ||
| Pantopoda | Phoxichilidiidae | Anoplodactylus pectinus | native | ||
| Ceramiales | Ceramiaceae | Anotrichium tenue | native | ||
| Charadriiformes | Laridae | Anous minutus | native | Black noddy | Black noddy |
| Charadriiformes | Laridae | Anous stolidus | native | Brown noddy | Brown noddy |
| Charadriiformes | Laridae | Anous tenuirostris | native | Lesser noddy | Sooty noddy |
| Dentaliida | Dentaliidae | Antalis antillaris | native | Antillean tuskshell | |
| Leptothecata | Plumulariidae | Antennella gracilis | native | ||
| Leptothecata | Halopterididae | Antennella secundaria | native | Sessile hydrozoans | |
| Valvatida | Goniasteridae | Anthenoides piercei | native | ||
| Littorinimorpha | Vitrinellidae | Anticlimax schumoi | native | ||
| Sipuncula | Phascolosomatidae | Antillesoma antillarum | native | Sipunculids | |
| Malacalcyonacea | Gorgoniidae | Antillogorgia elisabethae | native | Sea plume | |
| Ceramiales | Ceramiaceae | Antithamnion decipiens | native |