- Aardvark
- Aardwolf
- Abalone
- Abyssinian cat
- Abyssinian ground hornbill
- Acacia rat
- Achilles tang
- Acorn barnacle
- Acorn weevil
- Acorn woodpecker
- Acouchi (rodent resembling a squirrel)
- Adams stag-horned beetle
- Addax
- Adder
- Adelie penguin
- Admiral
- Admiral butterfly
- Adouri
- African augur buzzard
- African bush viper
- African civet
- African clawed frog
- African elephant
- African fish eagle
- African golden cat
- African ground hornbill
- African harrier hawk
- African hornbill
- African jacana
- African mole snake
- African paradise flycatcher
- African pied kingfisher
- African porcupine
- African rock python
- African wild cat
- African wild dog
- Agama
- Agouta (rodent resembling a mouse)
- Agouti (rodent resembling a squirrel)
- Airedale
- Aisan pied starling
- Akita Inu
- Alabama map turtle
- Alaska jingle
- Alaskan husky
- Alaskan malamute
- Albacore tuna
- Albatross
- Albertosaurus
- Albino
- Aldabra tortoise
- Allens big-eared bat
- Alligator
- Alligator gar
- Alligator snapping turtle
- Allosaurus
- Alpaca
- Alpine black swallowtail butterfly
- Alpine goat
- Alpine road guide tiger beetle
- Altiplano chinchilla mouse
- Amazon dolphin
- Amazon parrot
- Amazon tree boa
- Amber pen shell
- American alligator
- American avocet
- American badger
- American bittern
- American black vulture
- American cicada
- American crayfish
- American crocodile
- American crow
- American goldfinch
- American kestrel
- American lobster
- American marten
- American ratsnake
- American red squirrel
- American river otter
- American robin
- American toad
- American wigeon
- Amethyst gem clam
- Amethyst sunbird
- Amethystine python
- Ammonite
- Amoeba
- Amphibian
- Amphiuma
- Amur minnow
- Amur ratsnake
- Amur starfish
- Anaconda
- Anchovy
- Andean cat
- Andean cock-of-the-rock
- Andean condor
- Anemone
- Anemone crab
- Anemone shrimp
- Angel wing mussel
- Angelfish
- Anglerfish
- Angora
- Angwantibo
- Anhinga
- Animated
- Ankole
- Ankole-watusi
- Annas hummingbird
- Annelida
- Annelid
- Anole
- Anopheles
- Antarctic fur seal
- Antarctic giant petrel
- Anteater
- Antelope
- Antelope ground squirrel
- Antipodes green parakeet
- Ant
- Ant bear
- Ant lion
- Anura
- Aoudad
- Apatosaur
- Ape
- Aphid
- Apis dorsata laboriosa
- Aplomado falcon
- Aquatic leech
- Arabian horse
- Arabian oryx
- Arabian wild cat
- Aracari
- Arachnid
- Arawana
- Archaeocete
- Archaeopteryx
- Archer fish
- Arctic fox
- Arctic hare
- Arctic wolf
- Argali
- Argentine horned frog
- Argentine ruddy duck
- Argus fish
- Ariel toucan
- Arizona alligator lizard
- Ark shell
- Armadillo
- Armed crab
- Armed nylon shrimp
- Army ant
- Arrow crab
- Arrow worm
- Arrowana
- Arthropods
- Aruanas
- Asian constable butterfly
- Asian damselfly
- Asian elephant
- Asian lion
- Asian porcupine
- Asian small-clawed otter
- Asian trumpetfish
- Asian water buffalo
- Asiatic greater freshwater clam
- Asiatic lesser freshwater clam
- Asiatic mouflon
- Asiatic wild ass
- Asp
- Ass
- Assassin bug
- Astarte
- Astrangia coral
- Atlantic black goby
- Atlantic blue tang
- Atlantic ridley turtle
- Atlantic sharpnose puffer
- Atlantic spadefish
- Atlas moth
- Attwater's prairie chicken
- Auk
- Auklet
- Aurochs
- Australian curlew
- Australian freshwater crocodile
- Australian fur seal
- Australian kestrel
- Australian shelduck
- Australian Silky Terrier
- Avocet
- Axis deer
- Axolotl
- Aye-aye
- Aztec ant
- Azure-winged magpie
- Azure vase
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