Pa
- Palaeoendeinae Bamber, 2007 †
- Palaeoendeis Charbonnier, Vannier & Riou, 2007 †
- Palaeoisopoda †
- Palaeoisopodidae Dubinin, 1957 †
- Palaeoisopodus Broili, 1928 †
- Palaeopantopoda †
- Palaeopantopodidae Hedgpeth, 1955 †
- Palaeopantopus Broili, 1929 †
- Palaeopycnogonides Charbonnier, Vannier & Riou, 2007 †
- Palaeothea Bergstrom, Sturmer & Winter, 1980 †
- Pallenoides Stock, 1951
- Pallenopsidae Fry, 1978
- Pallenopsis Wilson, 1881
- Pantopipetta Stock, 1963
- Pantopoda
- Pantopoda incertae sedis
- Paranymphon Caullery, 1896
- Parapallene Carpenter, 1892
Pe
- Pentacolossendeis Hedgpeth, 1943
- Pentanymphon Hodgson, 1904
- Pentapycnon Bouvier, 1910
Ph
- Phoxichilidiidae Sars, 1891
- Phoxichilidium Milne-Edwards, 1840
- Phoxichilidoidea Sars, 1891
- Phoxiphilyra Stock, 1974
Pi
- Pigrogromitus Calman, 1927
Pr
- Proboehmia Stock, 1991
- Propallene Schimkewitsch, 1909
- Prototrygaeus Stock, 1975
Ps
- Pseudopallene Wilson, 1878
Py
- Pycnofragilia Stock, 1974
- Pycnogonidae Wilson, 1878
- Pycnogonoidea Pocock, 1904
- Pycnogonum Bruennich, 1764
- Pycnopallene Stock, 1950
- Pycnosomia Losina-Losinsky, 1961
- Pycnothea Loman, 1921