Ora
Oradarea Walker, 1903
- Oradarea acuminata Thurston, 1974
- Oradarea bidentata K.H. Barnard, 1932
- Oradarea crenulata Alonso de Pina, 1995
- Oradarea dawa Lowry & Myers, 2003
- Oradarea edentata K.H. Barnard, 1932
- Oradarea impressicauda K.H. Barnard, 1932
- Oradarea longimana (Boeck, 1871)
- Oradarea megalops (Nicholls, 1938)
- Oradarea novaezealandiae (Thomson, 1879)
- Oradarea ocellata Thurston, 1974
- Oradarea rossi Thurston, 1974
- Oradarea shoemakeri Pirlot, 1934
- Oradarea surera Alonso, 2012
- Oradarea tricarinata K.H. Barnard, 1932
- Oradarea tridentata K.H. Barnard, 1932
- Oradarea unidentata Thurston, 1974
- Oradarea walkeri Shoemaker, 1930
Crustacea → Malacostraca → Calliopioidea → Amphipoda → Calliopiidae
Oratosquilla Manning, 1968
- Oratosquilla fabricii (Holthuis, 1941)
- Oratosquilla kempi (Schmitt, 1931)
- Oratosquilla mauritiania (Kemp, 1913)
- Oratosquilla oratoria (De Haan, 1844)
Crustacea → Malacostraca → Stomatopoda → Squilloidea → Squillidae
Oratosquillina Manning, 1995
- Oratosquillina anomala (Tweedie, 1935)
- Oratosquillina asiatica (Manning, 1978)
- Oratosquillina berentsae Ahyong, 2001
- Oratosquillina gravieri (Manning, 1978)
- Oratosquillina inornata (Tate, 1883)
- Oratosquillina interrupta (Kemp, 1911)
- Oratosquillina manningi Ahyong, Chan & Liao, 2000
- Oratosquillina microps (Garcia & Manning, 1982)
- Oratosquillina nordica Ahyong & Chan, 2008
- Oratosquillina pentadactyla (Mannning, 1978)
- Oratosquillina perpensa (Kemp, 1911)
- Oratosquillina quinquedentata (Brooks, 1886)
- Oratosquillina stephensoni (Manning, 1978)
Crustacea → Malacostraca → Stomatopoda → Squilloidea → Squillidae
Orb
- Orbimorphus
- Orbione
- Orbitacolax
Orc
- Orchestia
- Orchestoidea
- Orchomene
- Orchomenella
- Orconectes
- Orcovita
Ore
- Oreades
- Oregonia
- Oregoniidae
- Oregoniscus
- Oreophorus
- Oreotlos
Ori
- Orientomysis
- Orientopsyllus
- Orientotlos
- Orionina
- Orithyia
- Orithyiidae
- Orithyioidea
- Oritoniscus
Orl
- Orlovibairdia
Orn
- Ornatoscalpellum
- Ornithocythere
Oro
- Orodillo
- Oroniscus
- Oropactes
- Orophryxus
- Oroscia
†Orozoe Barrande, 1872
- Orozoe marginata Maurer, 1885 †
- Orozoe mira Barrande, 1872 †
Crustacea → Oligostraca → Ostracoda → Ostracoda incertae sedis
Orp
- Orphelana
- Orphnoxanthus
Ort
- Orthagoriscicola
- Orthione
- Orthoconchoecia
- Orthocyclops
- Orthodillo
- Orthometopon
- Orthopagurus
- Orthopontonia
- Orthopsyllidae
- Orthopsyllidae
- Orthopsyllus
- Orthothelphusa
- Orthotheres