Between brackets is the number of accepted species

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- Mollusca (133 259)
- Subphylum Aculifera
- Subphylum Conchifera
- Subphylum Placophora accepted as Polyplacophora
- Superclass Aplacophora
- Class Amphineura accepted as Aculifera
- Class Bivalvia (25 079)
- Class Caudofoveata (143)
- Class Cephalopoda (1 917)
- Class Conchifera accepted as Bivalvia
- Class Cricoconarida † (1)
- Class Gastropoda (103 007)
- Subclass Amphigastropoda † (434)
- Subclass Angiogastropoda represented as Gastropoda
- Subclass Apogastropoda
- Subclass Caenogastropoda (53 817)
- Subclass Gastropoda incertae sedis (313)
- Subclass Heterobranchia (39 224)
- Infraclass "Lower Heterobranchia" (1 139)
- Infraclass Euthyneura (37 498)
- Subterclass Acteonimorpha (413)
- Subterclass Ringipleura (2 917)
- Superorder Nudipleura (2 748)
- Order Notaspidea accepted as Pleurobranchomorpha
- Order Nudibranchia (2 651)
- Suborder Aeolidina accepted as Cladobranchia
- Suborder Anthobranchia accepted as Doridina
- Suborder Cladobranchia (1 092)
- Infraorder Pseudoeuctenidiacea accepted as Doridoxoidea Bergh, 1899
- Parvorder Aeolidida accepted as Aeolidioidea Gray, 1827
- Parvorder Dendronotida accepted as Dendronotoidea Allman, 1845
- Parvorder Dendronotina accepted as Dendronotoidea Allman, 1845
- Parvorder Euarminida accepted as Arminoidea Iredale & O'Donoghue, 1923 (1841)
- Section Acleioprocta accepted as Fionoidea Gray, 1857
- Section Cleioprocta accepted as Aeolidioidea Gray, 1827
- Section Pleuroprocta accepted as Flabellinoidea Bergh, 1889
- Superfamily Aeolidiacea accepted as Aeolidioidea Gray, 1827
- Superfamily Aeolidioidea Gray, 1827 (338)
- Superfamily Arminoidea Iredale & O'Donoghue, 1923 (1841) (102)
- Superfamily Cladobranchia incertae sedis (8)
- Superfamily Dendronotoidea Allman, 1845 (199)
- Family Bornellidae Bergh, 1874 (12)
- Family Dactylopodidae Bonnevie, 1931 accepted as Phylliroidae Menke, 1830
- Family Dendronotidae Allman, 1845 (40)
- Family Dotidae Gray, 1853 (100)
- Family Fimbriidae O'Donoghue, 1926 accepted as Tethydidae Rafinesque, 1815
- Family Hancockiidae MacFarland, 1923 (6)
- Family Iduliidae Iredale & O'Donoghue, 1923 accepted as Dotidae Gray, 1853
- Family Lomanotidae Bergh, 1890 (7)
- Family Melibidae Forbes, 1844 accepted as Tethydidae Rafinesque, 1815
- Family Nectophyllirhoidae Hoffmann, 1922 accepted as Phylliroidae Menke, 1830
- Family Phylliroidae Menke, 1830 (3)
- Family Scyllaeidae Alder & Hancock, 1855 (10)
- Family Tethydidae Rafinesque, 1815 (21)
- Genus Chioraera A. Gould, 1852 accepted as Melibe Rang, 1829
- Genus Fimbria O'Donoghue, 1926 accepted as Tethys Linnaeus, 1767
- Genus Jacunia de Filippi, 1867 accepted as Melibe Rang, 1829
- Genus Melibaea accepted as Melibe Rang, 1829
- Genus Melibe Rang, 1829 (18)
- Genus Meliboea [sic] accepted as Melibe Rang, 1829
- Genus Propemelibe J. K. Allan, 1932 accepted as Melibe Rang, 1829
- Genus Tethys Linnaeus, 1767 (3)
- Subgenus Tethys (Aplysia) Linnaeus, 1767 accepted as Aplysia Linnaeus, 1767
- Subgenus Tethys (Neaplysia) J. G. Cooper, 1863 accepted as Aplysia Linnaeus, 1767
- Species Tethys (Neaplysia) californica (J. G. Cooper, 1863) accepted as Aplysia californica J. G. Cooper, 1863
- Species Tethys (Neaplysia) ritteri T. D. A. Cockerell, 1901 accepted as Aplysia californica J. G. Cooper, 1863
- Subgenus Tethys (Phycophila) A. Adams, 1861 accepted as Phycophila A. Adams, 1861
- Species Tethys californicus (J. G. Cooper, 1863) accepted as Aplysia californica J. G. Cooper, 1863
- Species Tethys capensis O'Donoghue, 1929 accepted as Aplysia juliana Quoy & Gaimard, 1832
- Species Tethys cervina Dall & C. T. Simpson, 1901 accepted as Aplysia cervina (Dall & C. T. Simpson, 1901)
- Species Tethys cornigera Macri, 1816 accepted as Tethys fimbria Linnaeus, 1767
- Species Tethys dominguensis Pruvot-Fol, 1954
- Species Tethys elegans W. H. Turton, 1932
- Species Tethys extraordinaria J. K. Allan, 1932 accepted as Aplysia extraordinaria (J. K. Allan, 1932)
- Species Tethys fimbria Linnaeus, 1767
- Species Tethys fimbriata [sic] accepted as Tethys fimbria Linnaeus, 1767
- Species Tethys floridensis Pilsbry, 1895 accepted as Aplysia fasciata Poiret, 1789
- Species Tethys hirasei Baba, 1936 accepted as Aplysia oculifera A. Adams & Reeve, 1850
- Species Tethys kurodai Baba, 1937 accepted as Aplysia kurodai (Baba, 1937)
- Species Tethys maculata (Rang, 1828) accepted as Aplysia maculata Rang, 1828
- Species Tethys modesta Thiele, 1910
- Species Tethys occidentalis (Odhner, 1936)
- Species Tethys operta Burne, 1906 accepted as Aplysia argus Rüppell & Leuckart, 1830
- Species Tethys panamensis Pilsbry, 1895 accepted as Aplysia dactylomela Rang, 1828
- Species Tethys parthenopeia Macri, 1816 accepted as Tethys fimbria Linnaeus, 1767
- Species Tethys parvula (Mörch, 1863) accepted as Aplysia parvula Mörch, 1863
- Species Tethys peasei Tryon, 1895 accepted as Aplysia peasei (Tryon, 1895)
- Species Tethys pilsbryi Letson, 1898 accepted as Aplysia pilsbryi (Letson, 1898)
- Species Tethys polyphylla Macri, 1816 accepted as Tethys fimbria Linnaeus, 1767
- Species Tethys pulmonica (Gould, 1852) accepted as Aplysia pulmonica A. Gould, 1852
- Species Tethys robertsi Pilsbry, 1895 accepted as Aplysia robertsi (Pilsbry, 1895)
- Species Tethys willcoxi (Heilprin, 1887) accepted as Aplysia fasciata Poiret, 1789
- Genus Tethys Linnaeus, 1758 accepted as Tethys Linnaeus, 1767
- Family Tethymelibidae Bergh, 1890 accepted as Tethydidae Rafinesque, 1815
- Superfamily Doridoxoidea Bergh, 1899 (2)
- Superfamily Fionoidea Gray, 1857 (303)
- Superfamily Flabellinoidea Bergh, 1889 accepted as Fionoidea Gray, 1857
- Superfamily Proctonotoidea Gray, 1853 (49)
- Superfamily Tritonioidea Lamarck, 1809 (91)
- Suborder Cladohepatica accepted as Cladobranchia
- Suborder Dexiarchia accepted as Cladobranchia
- Suborder Doridina (1 558)
- Suborder Euctenidiacea accepted as Doridina
- Suborder Holohepatica accepted as Doridina
- Suborder Nudibranchia incertae sedis (1)
- Order Pleurobranchida (97)
- Genus Abranchus [sic] accepted as Abrancha van Hasselt, 1824
- Genus Spongiodoris Pruvot-Fol, 1933
- Superorder Ringiculimorpha (169)
- Order Pleurobranchomorpha accepted as Pleurobranchida
- Genus Abrancha van Hasselt, 1824
- Subterclass Tectipleura (34 168)
- Superorder Euthyneura incertae sedis
- Infraclass Heterobranchia incertae sedis (478)
- Infraclass Mesoneura (109)
- Infraclass Opisthobranchia
- Infraclass Pulmonata
- Subclass Neomphaliones accepted as Vetigastropoda
- Subclass Neritimorpha (1 916)
- Subclass Orthogastropoda represented as Gastropoda
- Subclass Patellogastropoda (514)
- Subclass Prosobranchia
- Subclass Psilogastropoda represented as Gastropoda
- Subclass Vetigastropoda (6 789)
- 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 (1 381)
- Class Polyplaxiphora accepted as Polyplacophora
- Class Rostroconchia † (64)
- Class Scaphopoda (753)
- Class Solenoconchia accepted as Scaphopoda
- Class Solenogastres (313)
- Subclass Chaetodermomorpha accepted as Caudofoveata