- Macaca Lacépède 1799
- Macandrevia King 1859
- Machilus Nees
- Macridiscus Dall 1902
- Macrobrachium Bate 1868
- Macrocyclops Claus 1893
- Macromia Rambur 1842
- Macrophthalmus Desmarest 1823
- Macrophya Dahlbom 1835
- Macropodus Lacépède 1801
- Macropus Shaw 1790
- Macroramphosus Lacépède 1803
- Macroschisma Gray 1835
- Macrotrochela
- Mactra Linnaeus 1769
- Mactrinula Gray 1853
- Madrepora Linnaeus 1758
- Maeropsis Chevreux 1919
- Magadina Thomson 1915
- Magnolia Linné
- Mahidolia H.M. Smith 1932
- Makrokylindrus Stebbing 1912
- Malacomys Milne-Edwards 1877
- Malagazzia Bouillon 1984
- Malakichthys Döderlein 1883
- Mallotus Loureiro
- Mammanidula Sadovskaya in Skrjabin et al. 1952
- Mammomonogamus Ryzhikov 1948
- Mancinella Link 1807
- Mangarinus Herre 1943
- Maraenobiotus Mrázek 1893
- Mariaster A.H. Clark 1916
- Marmota Blumenbach 1779
- Marphysa Quatrefages 1865
- Marteilia Grizel, Comps, Bonami, Cousserans, Duthoit & Le Pennec 1974
- Marteilioides Comps, Park & Desportes 1987
- Martes Pinel 1792
- Mastigoniscus Lincoln 1985
- Mastonia Hinds 1843
- Mastophorus Diesing 1853
- Matsubaraea Taki 1953
- Matuta Weber 1795
- Mauremys Gray 1869
- Maurolicus Cocco 1838
- Maxillicosta Whitley 1935
- Mecistocirrus Railliet & Henry 1912
- Megabalanus Hoek 1913
- Megabeleses Takeuchi 1952
- Megachasma L.R. Taylor, Compagno & Struhsaker 1983
- Megachile Latreille 1802
- Megacyclops Kiefer 1927
- Megalodiscus Chandler 1923
- Megalomma Johansson 1926
- Megalops Lacépède 1803
- Megasyllis San Martín Hutchings & Aguado 2008
- Megathiris d'Orbigny 1847
- Megatomostethus Takeuchi 1933
- Megatrema Sowerby 1823
- Magellania Bayle 1880
- Megerlia King 1850
- Megerlina Deslongchamps 1884
- Meghimatium Hasselt 1823
- Meiacanthus Norman 1943
- Melampus Montfort 1810
- Melanips Walker in Haliday 1835
- Melanius Bonelli 1810
- Melanocorypha F. Boie 1828
- Melanoides Olivier 1804
- Melanostomias Brauer 1902
- Meles Brisson 1762
- Melicertissa Haeckel 1879
- Melicertum Goldfuss 1820
- Melita Leach 1814
- Menoidium Perty 1852
- Meotiorhynchus Sharp 1896
- Mercenaria Schumacher 1817
- Meretrix Lamarck 1799
- Meriones Illiger 1811
- Merulina Ehrenberg 1834
- Mesochaetopterus Potts 1914
- Mesechthistatus Breuning 1950
- Mesochra Boeck 1865
- Mesocyclops G.O. Sars 1914
- Mesogammarus Tzvetkova 1965
- Mesophoyx Sharpe 1894
- Mesopristes Bleeker 1845
- Mesosagitta Tokioka 1965
- Mesostenus Gravenhorst 1829
- Mesovelia Mulsant & Rey 1852
- Mespilia Desor 1846
- Messor Forel 1890
- Metacaprella Mayer 1903
- Metacyclops Kiefer 1927
- Metagonimus Katsurada 1912
- Metahuntemannia Smirnov 1946
- Metalia Gray 1855
- Metanephrops Jenkins 1972
- Metapenaeopsis Bouvier 1905
- Metapenaeus Wood Mason 1891
- Metaprotella Mayer 1890
- Metastrongylus Molin 1861
- Metazaptyx Pilsbry 1905
- Mexiconema Moravec, Vidal & Salgado-Maldonado 1992
- Michailocoris Štys 1985
- Microcanthus Swainson 1839
- Microcosmus Heller 1877
- Microcyclops Claus 1893
- Microdrosophila Malloch 1921
- Microeuraphia Poltarukha 1997
- Micrognathus Duncker 1912
- Microlepia C. Presl
- Micromys Dehne 1841
- Micropercops Fowler & B.A. Bean 1920
- Micropterus Lacépède 1802
- Microstomus Gottsche 1835
- Microtetrameres Travassos 1915
- Microtralia Dall 1894
- Microtus Schrank 1798
- Mikadotrochus Lindholm 1927
- Miliammina Heron-Allen & Earland 1930
- Millepora Linnaeus 1758
- Milvus Lacépède 1799
- Mimachlamys Iredale 1929
- Mirounga
- Miscanthus Andersson
- Misgurnus Lacépède 1803
- Misolampidius Solsky 1875
- Mitrapus Song & Chen 1976
- Mizuhopecten Masuda 1963
- Mobula Rafinesque 1810
- Modiolicola Aurivillius 1883
- Modiolus Lamarck 1799
- Moellendorffia Ancey 1887
- Moerella Fischer 1887
- Moerisia Boulenger 1907
- Mogera Pomel 1848
- Moguranema Yamaguti 1941
- Mola Kölreuter 1763
- Molgula Forbes 1848
- Molineus Cameron 1923
- Molinostrongylus Skarbilovitch 1934
- Molobratia Hull 1958
- Monacanthus Oken 1817
- Monalocoris Dahlbom 1851
- Moniliformis Travassos 1915
- Monocentris Bloch & Schneider 1801
- Monocorophium Bousfield & Hoover 1997
- Monoctenus Dahlbom 1835
- Monodonta Lamarck 1799
- Monodontomerus Westwood 1833
- Monoliropus Mayer 1903
- Monomitopus Alcock 1890
- Monommata Bartsch 1870
- Monomorium Mayr 1855
- Monopterus Lacépède 1800
- Monostyla Ehrenberg 1930
- Montastraea Blainville 1830
- Monticellina Laubier 1961
- Montifringilla Brehm 1828
- Montipora Blainville 1830
- Moolgarda Whitley 1945
- Mopalia Gray 1847
- Moraria Scott T. & Scott A. 1893
- Morbakka Gershwin 2008
- Morganiella Travassos 1937
- Morphnosoma Lutshnik 1915
- Mortonagrion Fraser 1920
- Morula Schumacher 1817
- Morus Linné 1753
- Mothocya Hope 1851
- Muellerius Cameron 1927
- Mugil Linnaeus 1758
- Mugilogobius Smitt 1899
- Mulloidichthys Whitley 1929
- Multatria Van Syoc & Newman 2010
- Munna Krøyer 1839
- Muraenesox McClelland 1844
- Murina
- Murravia Thomson 1916
- Mus Linnaeus 1758
- Musa Linné
- Musculium Link 1807
- Mustela Linnaeus 1758
- Mustelus Linck 1790
- Mya Linnaeus 1758
- Myagropsis Kützing 1843
- Myas Strum 1826
- Mycale Gray 1867
- Mycodrosophila Oldenberg 1914
- Mycteroperca Gill 1862
- Myersina Herre 1934
- Myliobatis Cuvier 1816
- Mylopharyngodon W.K.H. Peters 1881
- Myocastor Kerr 1792
- Myodes Pallas 1811
- Myopias Roger 1861
- Myotis Kaup 1829
- Myrmecina Curtis 1829
- Myrmentoma Forel 1912
- Myrmica Latreille 1804
- Myrsine Linné 1753
- Mystus Scopoli 1777
- Mytilaster Monterosato 1883
- Mytilicola Steuer 1902
- Mytilus Linnaeus 1758
- Myurella Hinds 1844
- Myoxocephalus Tilesius 1811