| Macoma | Macominae | Tellinidae | Tellinoidea | Mesostoma | Admetinae? | Cancellariidae | Mitroidea | |
| Macrocallista | Pitarinae | Veneridae | Veneroidea | Metaceritium | Metacerithiidae | Cerithioidea | ||
| Macrochisma | Fissurellinae | Fissurellidae | Fissurelloidea | Metaconulus | Calliostomatinae | Cirridae | Cirroidea | |
| Macrochlamis | Chlamydinae | Pectinidae | Pectinoidea | Metaphos | Photinae | Buccinidae | Buccinoidea | |
| Macromphalus | Vanikoridae | Vanikoroidea | Metula | Colubrariinae | Fasciolariidae | Columbelloidea | ||
| Macron | Buccininae | Buccinidae | Buccinoidea | Metulella | Pyreninae | Columbellidae | Columbelloidea | |
| Macrosolen | Psammobiinae | Psammobiidae | Tellinoidea | Micantapex | Clathurellinae | Conidae | Conoidea | |
| Macrozafra | Pyreninae | Columbellidae | Columbelloidea | Micrelenchus | Trochinae | Cirridae | Cirroidea | |
| Mactra | Mactrinae | Mactridae | Mactroidea | Microcolus | Fusininae | Fasciolariidae | Columbelloidea | |
| Mactrellona | Mactrinae | Mactridae | Mactroidea | Microdrillia | Clathurellinae | Conidae | Conoidea | |
| Magilus | Coralliophylidae | Muricoidea | Microstagon | Ungulinidae | Lucinoidea | |||
| Magnatica | Naticinae | Naticidae | Naticoidea | Microstelma | Rissoininae | Rissoinidae | Rissooidea | |
| Malarossia | Subfamily unknow | Veneridae | Veneroidea | Microsurcula | Cochlespirinae | Turridae | Conoidea | |
| Malea | Tonnidae | Tonnoidea | Microvoluta | Volutromitridae | Mitroidea | |||
| Mambrinia | Cassinae | Cassidae | Tonnoidea | Miltha | Milthinae | Lucinidae | Lucinoidea | |
| Mamiconus | Clathurellinae | Conidae | Conoidea | Mimachlamys | Chlamydinae | Pectinidae | Pectinoidea | |
| Mammilla | Polinicidae | Naticoidea | Miocardiopsis | Glossidae | Glossoidea | |||
| Mammites | Acanthoceratidae | Ammonoida | Miodomeris | Miodomeridinae | Carditidae | Carditoidea | ||
| Mangelia | Mangeliinae | Conidae | Conoidea | Mioerycina | Kelliinae | Kelliidae | Galeommatoidea | |
| Manuloma | Batillariinae | Batillariidae | Cerithioidea | Mioporomya | Poromyidae | Poromyoidea | ||
| Manzonia | Rissoinae | Rissoidae | Rissooidea | Miraclathurella | Crassispirinae | Turridae | Conoidea | |
| Maoricardium | Cardiinae | Cardiidae | Cardioidea | Mirascapha | Cylichnidae | Acteonoidea | ||
| Maoricolpus | Turritellinae | Turritellidae | Cerithioidea | Mirula | Terebrinae | Terebridae | Conoidea | |
| Maorimactra | Mactrinae | Mactridae | Mactroidea | Mitra | Mitrinae | Mitridae | Mitroidea | |
| Maorivetia | Cancellariinae | Cancellariidae | Mitroidea | Mitraria | Mitrinae | Mitridae | Mitroidea | |
| Marama | Venerinae | Veneridae | Veneroidea | Mitrella | Pyreninae | Columbellidae | Columbelloidea | |
| Marcia | Tapetinae | Veneridae | Veneroidea | Mitreola | Volutromitridae | Mitroidea | ||
| Margarites | Margaritinae | Cirridae | Cirroidea | Mitrolumna | Clathurellinae | Conidae | Conoidea | |
| Marginella | Marginellinae | Marginellidae | Volutoidea | Mizuhopecten | Patinopectinae | Pectinidae | Pectinoidea | |
| Margineulima | Eulimidae | Eulimoidea | Modiolula | Modiolinae | Mytilidae | Mytiloidea | ||
| Mariacolpus | Turritellinae | Turritellidae | Cerithioidea | Modiolus | Modiolinae | Mytilidae | Mytiloidea | |
| Marianarona | Cancellariinae | Cancellariidae | Mitroidea | Modulus | Modulidae | Cerithioidea | ||
| Mariaturricula | Clavatulinae | Turridae | Conoidea | Moerella | Tellininae | Tellinidae | Tellinoidea | |
| Marikellia | Kelliinae | Kelliidae | Galeommatoidea | Monia | Anomiidae | Anomioidea | ||
| Marinula | Pedipedinae | Ellobiidae | Ellobioidea | Monilea | Umboniinae | Cirridae | Cirroidea | |
| Martesia | Martesiinae | Pholadidae | Pholadoidea | Monilispira | Crassispirinae | Turridae | Conoidea | |
| Marvacrassatell | Crassatellinae | Crassatellidae | Crassatelloidea | Monitilora | Myrteinae | Lucinidae | Lucinoidea | |
| Massyla | Cancellariinae | Cancellariidae | Mitroidea | Monocirsus | Cymatiinae | Ranellidae | Tonnoidea | |
| Mataxa | Cancellariinae | Cancellariidae | Mitroidea | Monodonta | Trochinae | Cirridae | Cirroidea | |
| Mathilda | Mathildidae | Architectonicoidea | Monophorus | Trphorinae | Triphoridae | Ptenoglossa | ||
| Mauidrillia | Crassispirinae | Turridae | Conoidea | Monotis | Monotidae | Pectinoidea | ||
| Mauira | Zidoninae | Volutidae | Volutoidea | Montacuta | Montacutinae | Montacutidae | Galeommatoidea | |
| Mauithoe | Zidoninae | Volutidae | Volutoidea | Monterosatus | Davilinae | Mesodesmatidae | Mactroidea | |
| Maurea | Calliostomatinae | Cirridae | Cirroidea | Montia | Volutidae | Volutoidea | ||
| Medioriopsis | Fossaridae | Vanikoroidea | Morea | Moreinae | Muricidae | Muricoidea | ||
| Megacardita | Venericardiinae | Carditidae | Carditoidea | Morum | Moruminae | Harpidae | Muricoidea | |
| Megangulus | Tellininae | Tellinidae | Tellinoidea | Mulinia | Mactrinae | Mactridae | Mactroidea | |
| Megaxinus | Lucininae | Lucinidae | Lucinoidea | Munditia | Liotiinae | Turbinidae | Trochoidea | |
| Meiocardia | Glossidae | Glossoidea | Murex | Muricinae | Muricidae | Muricoidea | ||
| Meioceras | Caecidae | Rissooidea | Murexiella | Muricopsinae | Muricidae | Muricoidea | ||
| Melanatria | Melanatrinae | Pleuroceridae | Cerithioidea | Murexsul | Muricopsinae | Muricidae | Muricoidea | |
| Melanella | Eulimidae | Eulimoidea | Muricanthus | Muricinae | Muricidae | Muricoidea | ||
| Melanopsis | Melanopsidae | Cerithioidea | Muricopsis | Muricopsinae | Muricidae | Muricoidea | ||
| Melaraphe | Littorininae | Littorinidae | Littorinoidea | Musculus | Modiolinae | Mytilidae | Mytiloidea | |
| Melongena | Melongeninae | Melongenidae | Buccinoidea | Musculus | Crenellinae | Mytilidae | Mytiloidea | |
| Melosia | Venerinae | Veneridae | Veneroidea | Mya | Myinae | Myidae | Myoidea | |
| Menestho | Odostomellinae | Pyramidellidae | Pyramidelloidea | Myadora | Myochamidae | Pandoroidea | ||
| Menetus | Helisomatinae | Planorbidae | Planorbioidea | Myalina | Myalinidae | Ambonychioidea | ||
| Mercenaria | Chioninae | Veneridae | Veneroidea | Myrene | Neomiodontidae | Arcticoidea | ||
| Meretrix | Meretricinae | Veneridae | Veneroidea | Myrtea | Myrteinae | Lucinidae | Lucinoidea | |
| Merica | Cancellariinae | Cancellariidae | Mitroidea | Mysella | Mysellinae | Montacutidae | Galeommatoidea | |
| Meroena | Sunettinae | Veneridae | Veneroidea | Mysia | Petricolidae | Veneroidea | ||
| Mesalia | Turritellinae | Turritellidae | Cerithioidea | Mytilopsis | Dreissenidae | Dreissenoidea | ||
| Mesodesma | Mesodesmatinae | Mesodesmatidae | Mactroidea | Mytilus | Mytilinae | Mytilidae | Mytiloidea | |
| Mesoginella | Marginellinae | Marginellidae | Volutoidea | Myurella | Terebrinae | Terebridae | Conoidea | |
| Mesopeplum | Pectininae | Pectinidae | Pectinoidea | |||||