Between brackets is the number of accepted species

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- Mollusca (132 848)
- Subphylum Aculifera
- Subphylum Conchifera
- Subphylum Placophora accepted as Polyplacophora
- Superclass Aplacophora
- Class Amphineura accepted as Aculifera
- Class Bivalvia (25 011)
- Subclass Autobranchia (23 297)
- Infraclass Heteroconchia (16 637)
- Subterclass Archiheterodonta (1 208)
- Subterclass Euheterodonta (11 356)
- Subterclass Heterodonta
- Subterclass Palaeoheterodonta (4 072)
- Order Trigoniida (1 482)
- Superfamily Megatrigonioidea van Hoepen, 1929 † (336)
- Family Buchotrigoniidae H. A. Leanza, 1993 † (13)
- Family Iotrigoniidae Saveliev, 1958 † (36)
- Subfamily Iotrigoniinae Saveliev, 1958 † accepted as Iotrigoniidae Saveliev, 1958 †
- Genus Andivaugonia H. A. Leanza, 1993 † (1)
- Genus Baxoitrigonia Stiller & J.-H. Chen, 2019 † (1)
- Genus Grandigonia M. R. Cooper, 2015 † (1)
- Genus Iotrigonia van Hoepen, 1929 † (12)
- Genus Lambertiella M. R. Cooper, 1991 † accepted as Andivaugonia H. A. Leanza, 1993 †
- Genus Levytrigonia M. R. Cooper, 2015 † (1)
- Genus Mayesella M. R. Cooper, 2015 † (9)
- Genus Perezella M. R. Cooper, 2015 † accepted as Perezigonia Ceccolini & Cianferoni, 2021 †
- Genus Perezigonia Ceccolini & Cianferoni, 2021 † (2)
- Genus Tamaragonia M. R. Cooper, 2015 † (5)
- Genus Zaletrigonia Skwarko, 1963 † (4)
- Family Megatrigoniidae van Hoepen, 1929 † (73)
- Family Pterotrigoniidae van Hoepen, 1929 † (214)
- Superfamily Myophorelloidea T. Kobayashi, 1954 † (376)
- Superfamily Pseudocardinioidea Martinson, 1961 † (176)
- Superfamily Trigonioidea Lamarck, 1819 (350)
- Superfamily Trigonioidoidea L. R. Cox, 1952 † (226)
- Superfamily Trigonodoidea Modell, 1942 † (18)
- Order Unionida (2 579)
- Family Lyrodesmatidae P. Fischer, 1886 † (8)
- Family Pseudarcidae Scarlato & Starobogatov, 1979 † (3)
- Family Thoraliidae N. J. Morris, 1980 †
- Superorder Heteroconchia incertae sedis † (1)
- Infraclass Pteriomorphia (6 660)
- Subclass Bivalvia incertae sedis (7)
- Subclass Palaeotaxodonta accepted as Nuculida
- Subclass Paleoheterodonta accepted as Palaeoheterodonta
- Subclass Protobranchia (1 365)
- Infraclass Cryptodonta † (342)
- Class Caudofoveata (143)
- Class Cephalopoda (1 834)
- Class Conchifera accepted as Bivalvia
- Class Cricoconarida † (1)
- Class Gastropoda (102 752)
- Class Lamellibranchiata accepted as Bivalvia
- Class Loricata accepted as Polyplacophora
- Class Mollusca incertae sedis † (372)
- Class Monoplacophora (229)
- Class Pelecypoda accepted as Bivalvia
- Class Polyplacophora (1 377)
- Class Polyplaxiphora accepted as Polyplacophora
- Class Rostroconchia † (64)
- Class Scaphopoda (752)
- Class Solenoconchia accepted as Scaphopoda
- Class Solenogastres (313)
- Subclass Chaetodermomorpha accepted as Caudofoveata