Mactridae

These clams have two short siphons, each with a horny sheath. The shell is shaped like a rounded-cornered equilateral triangle and there is a slight gape at the posterior. Each valve bears two cardinal teeth with four lateral teeth on the right valve and two on the left. The foot is white and wedge-shaped. They mostly inhabit the neritic zone.

Trough shells burrow in sand or fine gravel and never in muddy substrates.

According to the World Register of Marine Species (2025), this family contains 56 genera and is split into the following subfamilies:

Subfamily Darininae

• †Darcinia Clark, 1946
• Darina J. E. Gray, 1853

Subfamily Lutrariinae

• Eastonia J. E. Gray, 1853
• Heterocardia Deshayes, 1855
• Lutraria Lamarck, 1799
• Meropesta Iredale, 1929
• Standella J. E. Gray, 1853
• Tresus J. E. Gray, 1853
• Zenatia J. E. Gray, 1853
• Zenatina Gill & Darragh, 1963

Subfamily Mactrinae

• †Allomactra Tomlin, 1931
• Austromactra Iredale, 1930
• Barymactra Cossmann, 1909
• Coelomactra Dall, 1895
• Crassula Marwick, 1948
• Cyclomactra Dall, 1895
• Diaphoromactra Iredale, 1930
• Harvella J. E. Gray, 1853
• Huberimactra Cosel & Gofas, 2018
• Leptospisula Dall, 1895
• Mactra Linnaeus, 1767
• Mactrella J. E. Gray, 1853
• Mactrellona J. G. Marks, 1951
• Mactrinula J. E. Gray, 1853
• Mactromeris Conrad, 1868
• Mactrotoma Dall, 1894
• Maorimactra H. J. Finlay, 1928
• Mulinia J. E. Gray, 1837
• Oxyperas Mörch, 1853
• †Pseudocardium Gabb, 1866
• Rangia Desmoulins, 1832
• †Sarmatimactra Korobkov, 1954
• Scalpomactra H. J. Finlay, 1928
• Scissodesma Gray, 1837
• Simomactra Dall, 1894
• Spisula J. E. Gray, 1837
• Trinitasia Maury, 1928
• Tumbeziconcha Pilsbry & Olsson, 1935
• Mactrona Marwick, 1952
• Petromactra Saul, 1973

Subfamily Resaniinae

• Resania J. E. Gray, 1853

Subfamily Tanysiphoninae

• Tanysiphon W. H. Benson, 1858

Incertae sedis

• †Aktschagylia Starobogatov, 1970
• †Aliomactra Stephenson, 1952
• †Andrussella Korobkov, 1954
• †Avimactra Andrusov, 1905
• †Caspimactra A. A. Ali-Zade & Kabakova, 1969
• †Chersonimactra Paramonova, 1978
• †Cryptomactra Andrussow, 1902
• †Cymbophora Gabb, 1869
• †Eopapyrina Woodring, 1982
• †Geltena Stephenson, 1946
• †Ionesimactra Signorelli, 2023
• †Kirghizella Andrusov, 1902
• †Mactrodesma Conrad, 1869
• Mactrona Marwick, 1952
• †Mulinoides Olsson, 1944
• †Nelltia Stephenson, 1952
• †Nymphactra Stilwell & Zinsmeister, 1992
• †Ovamactra Woodring, 1982
• Petromactra Saul, 1973
• †Planimactra Ionesi, 1986
• †Podolimactra Ionesi, 1986
• †Praerangia Cossmann, 1908
• †Priscomactra Stephenson, 1952
• †Pseudomactra Steklov, 1960
• †Pteroluter Saul, 1973
• †Stereomactra Stewart, 1930
• †Stiphromactra Böhm, 1929
• †Tenuimactra Garvie, 1996
• †Willimactra Saul, 1973
• †Zenatiopsis Tate, 1880