Ara
- Arachnomysis
- Arachnopsis
- Arachnothelphusa
- Araiopontonia
- Araleptochelia
Araphura Bird & Holdich, 1984
- Araphura arvedlundi Larsen & Araújo-Silva, 2009
- Araphura breviaria Dojiri & Sieg, 1997
- Araphura brevimanus (Lilljeborg, 1864)
- Araphura curticauda Larsen, 2005
- Araphura cuspirostris Dojiri & Sieg, 1997
- Araphura doutagalla Błażewicz-Paszkowycz & Bamber, 2012
- Araphura elongata (Shiino, 1970)
- Araphura extensa Larsen, 2003
- Araphura filiformis (Lilljeborg, 1864)
- Araphura higginsi Sieg & Dojiri, 1989
- Araphura io Bamber, 2005
- Araphura joubinensis Sieg & Dojiri, 1989
- Araphura macrobelone Błażewicz-Paszkowycz, Bamber & Cunha, 2011
- Araphura parabrevimanus (Lang, 1968)
- Araphura pygmothymos Błażewicz-Paszkowycz & Bamber, 2012
- Araphura rectifrons (Kudinova-Pasternak, 1973)
- Araphura spinithenari Larsen, 2005
- Araphura whakarakaia Bird, 2011
- Araphura yarra Błażewicz-Paszkowycz & Bamber, 2012
Crustacea → Malacostraca → Tanaidacea → Paratanaoidea → Tanaellidae
- Aratus
Arc
Arcangeloscia Taiti & Ferrara, 1980
- Arcangeloscia buettneroides Schmalfuss & Ferrara, 1978
- Arcangeloscia congolensis Taiti & Ferrara, 1980A
- Arcangeloscia curvitelson Ferrara & Schmalfuss, 1983
- Arcangeloscia longistyla Ferrara & Schmalfuss, 1983
- Arcangeloscia meridionalis Taiti & Ferrara, 1987
- Arcangeloscia microphthalma Schmalfuss & Ferrara, 1978
- Arcangeloscia porcellioides Budde-Lund, 1904
- Arcangeloscia puylaerti Schmalfuss & Ferrara, 1978
Crustacea → Malacostraca → Isopoda → Oniscidea → Philosciidae
- Arcania
- Archaeobalanidae
- Archaeobalanidae
Archaeocuma Bacescu, 1972
- Archaeocuma peruanum Bacescu, 1972
Animalia → Arthropoda → Malacostraca → Cumacea → Lampropidae
- Archaeomysis
Archaeoscia Vandel, 1973
- Archaeoscia singularis Vandel, 1973
Crustacea → Malacostraca → Isopoda → Ligiamorpha → Philosciidae
- Archaeoscina
- Archaeoscinidae
- Archepleuroxus
- Archiacasta
- Archiconchoecemma
- Archiconchoecerra
- Archiconchoecetta
- Archiconchoecia
- Archiconchoecilla
- Archiconchoecinna
- Archiconchoecissa
- Archileptastacus
- Archinotodelphyidae
- Archinotodelphyidae
- Archinotodelphys
- Archisenia
- Arcitalitrus
- Arcoscalpellum
- Arcotheres
- Arcticotantulus
- Arctides
- Arctocyclopina
- Arctodiaptomus
- Arctolembos
- Arctopleustes
- Arctopontius
- Arctopsis
- Arctotanais
- Arcturidae
- Arcturides
- Arcturididae
- Arcturina
- Arcturinella
- Arcturinoides
- Arcturocheres
- Arcturopsis
- Arcturus
- Arculfia
Are
- Arenaeus
- Arenocaris
- Arenolaophonte
- Arenopontia
- Arenosetella
Areosquilla Manning, 1976
- Areosquilla hanseni Manning, 1976
- Areosquilla indica (Hansen, 1926)
- Areosquilla interstincta Manning, 1976
Crustacea → Malacostraca → Stomatopoda → Squilloidea → Squillidae
- Aretopsis
Arg
- Argathona
- Argeia
- Argeiopsis
- Argestes
- Argestidae
- Argestidae
- Argilloecia
- Argis
- Argissa
- Argissidae
- Argulidae
- Argulidae
- Arguloida
- Arguloida
- Argulus
Arh
- Arhaphuroides
- Arhina
Ari
- Arietellidae
- Arietellidae
- Arietellus
- Aristaeomorpha
- Aristaeopsis
- Aristeidae
- Aristeus
- Aristias
- Aristiidae
- Aristiopsis
Arm
- Armadillidae
- Armadillidiidae
- Armadillidium
- Armadillo
- Armadilloniscus
- Armases
- Armatalona
- Armatobalanus
- Armatognathia
- Armaturatanais
Aro
- Aroui
Arr
- Arrhinopsis
- Arrhis
Art
- Artemesia
Artemia Leach, 1819
- Artemia franciscana Kellog, 1906
- Artemia gracilis Verrill, 1869
- Artemia monica Verrill, 1869
- Artemia persimilis Piccinelli & Prosdocimi, 1968
- Artemia salina (Linnaeus, 1758)
- Artemia sinica Cai, 1989
- Artemia tibetiana Abatzopoulos, Zhang & Sorgeloos, 1998
- Artemia urmiana Günther, 1899
Crustacea → Branchiopoda → Anostraca → Artemiidae
Porodica Artemiidae Grochowski, 1895
- Artemia Leach, 1819
Crustacea → Branchiopoda → Anostraca
- Artemiopsis
- Artesia
- Artesiidae
- Arthromysis
- Arthrophryxus
- Arthrura
- Arthurhumesia
- Arthuricornua
Artopoles Barnard, 1920
- Artopoles capensis Barnard, 1955
- Artopoles natalis Barnard, 1920
Crustacea → Malacostraca → Isopoda → Sphaeromatoidea → Sphaeromatidae
- Artopotamon
- Artotrogidae
- Artotrogidae
- Artotrogus
- Artystone
Aru
- Arubolana
- Aruga
- Arugella