Classification of the gastropod molluscs in the three traditional subclasses of the Prosobranchs (marine snails), Opisthobranchs (sea slugs and sea hares among others) and Pulmonates (land snails and land slugs) has ruled from the first third of the 20th century until very recently, and still remains in most Zoology textbooks.

Modern phylogenetic evaluation techniques, based on morphological, embryological, molecular and combined characters, have allowed to demonstrate that the phylogenies of these groups are not that simple and there has been a very significant change in different groups when considering evolutionary independent lines (monophyletic).

For these reasons some taxa have been abandoned, like the traditional subclass of the Prosobranchs (abandoned as paraphyletic) that has now been divided into the subclasses Patellogastropoda, Vetigastropoda, Cocculiniformia, Neritimorpha, Caenogastropoda and the small group of Neomphalina.

The concepts of Opisthobranchs and Pulmonates (until now Infraclases of the Heterobranchia, joined under the term Euthyneura based on the structure of their nervous system) have been replaced by the following groupings with category of Subterclass: Acteonimorpha (grouping the traditional Acteonoidea and Rissoelloidea ), Tectipleura (grouping the traditional Euopisthobranchia and Pulmonata) and Ringipleura (grouping Nudipleura and Ringiculimorpha).

The bases of this new classification are in the enormous taxonomic work by Bouchet & Rocroi (2005), recently updated by Bouchet et al. (2017) and followed by World Register of Marine Species (WoRMS).

The taxonomic synopsis of each species descriptive sheets at OPK-Opisthobranchs are basically according to these ideas.

The current taxonomic scheme of the gastropods would be as follows:

  • Class Gastropoda Cuvier, 1795
    • Subclass Caenogastropoda
    • Subclass Cocculiniformia
    • Subclass Neomphalina
    • Subclass Neritimorpha
    • Subclass Patellogastropoda
    • Subclass Vetigastropoda
    • Subclass Gastropoda incertae sedis †
    • Subclass Heterobranchia

Except for Heterobranchia, the previous subclasses correspond to groups of former “Prosobranchs”, preferably marine snails, of separated genders, with pallial cavity and typical gills. The groups marked with the dagger (†) are fossil taxa.

  • Subclass Heterobranchia Burmeister, 1837: Includes the Gastropoda that have a gill origin different from that of the other Gastropods (former Prosobranchs), and comprises species marine, freshwater and terrestrial snails.            
    • Infraclass “lower Heterobranchia: includes shelled species of marine and freshwater snails, of still uncertain relationships, which had traditionally been considered prosobranchs or opisthobranchs. Until recently it also included the superfamilies Acteonoidea, Pyramidelloidea and Ringiculoidea (for some time they have not been considered opisthobranchs) but now these superfamilies are considered again within the Euthyneura and therefore no longer belong to this group, actually formed by:
      • Superfamily Architectonicoidea Gray, 1850
      • Superfamily Cimoidea Warén, 1993
      • Superfamily Mathildoidea Dall, 1889
      • Superfamily Murchisonelloidea T. L. Casey, 1904
      • Superfamily Omalogyroidea G.O. Sars, 1878
      • Superfamily Orbitestelloidea Iredale, 1917
      • Superfamily Rhodopoidea Ihering, 1876
      • Superfamily Valvatoidea Gray, 1840
    • Infraclass [unassigned] Heterobranchia: includes a few groups of the fossil register whose adscription to the other groups is not clear.
      • Superfamily Acteonelloidea Gill, 1871 †
      • Family Dolomitellidae Bandel, 1994 †
      • Family Kuskokwimiidae Frýda & Blodgett, 2001 †
      • Family Misurinellidae Bandel, 1994 †
      • Superfamily Nerineoidea Zittel, 1873 †
      • Superfamily Streptacidoidea Knight, 1931 †
    • Infraclass Euthyneura, includes those that were traditionally considered Opisthobranchs (slugs almost exclusively marine, with or without shell) and Pulmonates (terrestrial and marine slugs and snails).
      • Subterclass Acteonimorpha
        • Superfamily Acteonoidea d’Orbigny, 1843, considered until recently within Cephalaspidea sensu lato or as Architectibranchia.
          • Family Acteonidae d’Orbigny, 1843
          • Family Aplustridae Gray, 1847
          • Family Bullinidae Gray, 1850
          • Family Cylindrobullinidae Wenz, 1938 †
          • Family Tubiferidae Cossmann, 1895 †
          • Family Zardinellidae Bandel, 1994 †
        • Superfamily Rissoelloidea Gray, 1850
          • Family Rissoellidae Gray, 1850
      • Subterclass Ringipleura
        • Superorder Nudipleura, its members share characters of the circulatory system.
          • Order Nudibranchia
            • Suborder Cladobranchia
              • Superfamily Aeolidioidea Gray, 1827
                • Family Aeolidiidae Gray, 1827
                • Family Babakinidae Roller, 1973
                • Family Facelinidae Bergh, 1889
                • Family Flabellinopsidae Korshunova, Martynov, Bakken, Evertsen, Fletcher, Mudianta, Saito, Lundin, Schrödl & Picton, 2017
                • Family Glaucidae Gray, 1827
                • Family Notaeolidiidae Eliot, 1910
                • Family Piseinotecidae Edmunds, 1970
                • Family Pleurolidiidae Burn, 1966
              • Superfamily Arminoidea Iredale & O’Donoghue, 1923 (1841)
                • Family Arminidae Iredale & O’Donoghue, 1923 (1841)
                • Family Doridomorphidae Er. Marcus & Ev. Marcus, 1960 (1908)
              • Superfamily Dendronotoidea Allman, 1845
                • Family Bornellidae Bergh, 1874
                • Family Dendronotidae Allman, 1845
                • Family Dotidae Gray, 1853
                • Family Hancockiidae MacFarland, 1923
                • Family Lomanotidae Bergh, 1890
                • Family Scyllaeidae Alder & Hancock, 1855
                • Family Tethydidae Rafinesque, 1815
              • Superfamily Doridoxoidea Bergh, 1899
                • Family Doridoxidae Bergh, 1899
              • Superfamily Fionoidea Gray, 1857
                • Family Abronicidae Korshunova, Martynov, Bakken, Evertsen, Fletcher, Mudianta, Saito, Lundin, Schrödl & Picton, 2017
                • Family Apataidae Korshunova, Martynov, Bakken, Evertsen, Fletcher, Mudianta, Saito, Lundin, Schrödl & Picton, 2017
                • Family Calmidae Iredale & O’Donoghue, 1923
                • Family Cumanotidae Odhner, 1907
                • Family Cuthonellidae M. C. Miller, 1977
                • Family Cuthonidae Odhner, 1934
                • Family Embletoniidae Pruvot-Fol, 1954
                • Family Eubranchidae Odhner, 1934
                • Family Fionidae Gray, 1857
                • Family Flabellinidae Bergh, 1889
                • Family Murmaniidae Korshunova, Martynov, Bakken, Evertsen, Fletcher, Mudianta, Saito, Lundin, Schrödl & Picton, 2017
                • Family Paracoryphellidae M. C. Miller, 1971
                • Family Pinufiidae Er. Marcus & Ev. Marcus, 1960
                • Family Samlidae Korshunova, Martynov, Bakken, Evertsen, Fletcher, Mudianta, Saito, Lundin, Schrödl & Picton, 2017
                • Family Tergipedidae Bergh, 1889
                • Family Trinchesiidae F. Nordsieck, 1972
                • Family Unidentiidae Millen & Hermosillo, 2012
              • Superfamily Proctonotoidea Gray, 1853
                • Family Curnonidae d’Udekem d’Acoz, 2017
                • Family Dironidae Eliot, 1910
                • Family Lemindidae Griffiths, 1985
                • Family Proctonotidae Gray, 1853
              • Superfamily Tritonioidea Lamarck, 1809
                • Family Tritoniidae Lamarck, 1809
            • Suborder Doridina
              • Infraorder Bathydoridoidei
                • Superfamily Bathydoridoidea Bergh, 1891
              • Infraorder Doridoidei
                • Superfamily Doridoidea Rafinesque, 1815
                  • Family Actinocyclidae O’Donoghue, 1929
                  • Family Cadlinidae Bergh, 1891
                  • Family Chromodorididae Bergh, 1891
                  • Family Discodorididae Bergh, 1891
                  • Family Dorididae Rafinesque, 1815
                  • Subfamily Miamirinae Bergh, 1891
                • Superfamily Onchidoridoidea Gray, 1827
                  • Family Akiodorididae Millen & Martynov, 2005
                  • Family Calycidorididae Roginskaya, 1972
                  • Family Corambidae Bergh, 1871
                  • Family Goniodorididae H. Adams & A. Adams, 1854
                  • Family Onchidorididae Gray, 1827
                • Superfamily Phyllidioidea Rafinesque, 1814
                  • Family Dendrodorididae O’Donoghue, 1924 (1864)
                  • Family Mandeliidae Valdés & Gosliner, 1999
                  • Family Phyllidiidae Rafinesque, 1814
                • Superfamily Polyceroidea Alder & Hancock, 1845
                  • Family Aegiridae P. Fischer, 1883
                  • Family Hexabranchidae Bergh, 1891
                  • Family Okadaiidae Baba, 1930
                  • Family Polyceridae Alder & Hancock, 1845
          • Order Pleurobranchida, former Notaspideans
            • Superfamily Pleurobranchoidea Gray, 1827
              • Family Pleurobranchaeidae Pilsbry, 1896
              • Family Pleurobranchidae Gray, 1827
              • Family Quijotidae Ortea, Moro & Bacallado, 2016
        • Superorder Ringiculimorpha, considered until recently within Cephalaspidea sensu lato or as Architectibranchia. The most primitive of the group.
          • Superfamily Ringiculoidea Philippi, 1853
            • Family Ringiculidae Philippi, 1853
      • Subterclass Tectipleura (former Euopisthobranchia + Panpulmonata)
        • Superorder Acochlidiimorpha
          • Superfamíly Acochlidioidea Küthe, 1935
            • Family Acochlidiidae Küthe, 1935
            • Family Aitengidae Swennen & Buatip, 2009
            • Family Bathyhedylidae Neusser, Jörger, Lodde-Bensch, E. E. Strong & Schrödl, 2016
            • Family Hedylopsidae Odhner, 1952
            • Family Pseudunelidae Rankin, 1979
            • Family Tantulidae Rankin, 1979
          • Superfamíly Parhedyloidea Thiele, 1931
            • Family Asperspinidae Rankin, 1979
            • Family Parhedylidae Thiele, 1931
        • Order Aplysiida, former Anaspidea (=Aplysiomorpha)
          • Superfamíly Akeroidea Mazzarelli, 1891
            • Family Akeridae Mazzarelli, 1891
          • Superfamíly Aplysioidea Lamarck, 1809
            • Family Aplysiidae Lamarck, 1809
        • Order Cephalaspidea, former Bullomorpha
          • Superfamíly Bulloidea Gray, 1827
            • Family Bullidae Gray, 1827
            • Family Retusidae Thiele, 1925
            • Family Rhizoridae Dell, 1952
            • Family Tornatinidae P. Fischer, 1883
          • Superfamíly Cylichnoidea H. Adams & A. Adams, 1854
            • Family Colinatydidae Oskars, Bouchet & Malaquias, 2015
            • Family Cylichnidae H. Adams & A. Adams, 1854
            • Family Diaphanidae Odhner, 1914 (1857)
            • Family Eoscaphandridae Chaban & Kijashko, 2016
            • Family Mnestiidae Oskars, Bouchet & Malaquias, 2015
          • Superfamíly Haminoeoidea Pilsbry, 1895
            • Family Haminoeidae Pilsbry, 1895
          • Superfamíly Newnesioidea Moles, Wägele, Schrödl & Avila, 2017
            • Family Newnesiidae Moles, Wägele, Schrödl & Avila, 2017
          • Superfamíly Philinoidea Gray, 1850 (1815)
            • Family Aglajidae Pilsbry, 1895 (1847)
            • Family Alacuppidae Oskars, Bouchet & Malaquias, 2015
            • Family Colpodaspididae Oskars, Bouchet & Malaquias, 2015
            • Family Gastropteridae Swainson, 1840
            • Family Laonidae Pruvot-Fol, 1954
            • Family Philinidae Gray, 1850 (1815)
            • Family Philinoglossidae Hertling, 1932
            • Family Philinorbidae Oskars, Bouchet & Malaquias, 2015
            • Family Scaphandridae G.O. Sars, 1878
        • Order Pteropoda, of pelagic habits, they can swim thanks to body extensions that they use as swimming fins.
          • Suborder Pseudothecosomata, with a cartilaginous shell, feeds on phytoplankton.
            • Superfamily Cymbulioidea Gray, 1840
              • Family Cymbuliidae Gray, 1840
              • Family Desmopteridae Chun, 1889
              • Family Peraclidae Tesch, 1913
          • Suborder Euthecosomata, with a calcified shell, feeds on phytoplankton.
            • Superfamily Cavolinioidea Gray, 1850 (1815)
              • Family Cavoliniidae Gray, 1850 (1815)
              • Family Cliidae Jeffreys, 1869
              • Family Creseidae Rampal, 1973
              • Family Praecuvierinidae A. Janssen, 2006 †
              • Family Sphaerocinidae A. W. Janssen & Maxwell, 1995 †
            • Superfamily Limacinoidea Gray, 1840
              • Family Limacinidae Gray, 1840
          • Suborder Gymnosomata, without a shell, carnivorous, feeds on Euthecosomata and Pseudothecosomata.
            • Superfamily Clionoidea Rafinesque, 1815
              • Family Clionidae Rafinesque, 1815
              • Family Cliopsidae O. G. Costa, 1873
              • Family Notobranchaeidae Pelseneer, 1886
              • Family Pneumodermatidae Latreille, 1825
            • Superfamily Hydromyloidea Pruvot-Fol, 1942 (1862)
              • Family Hydromylidae Pruvot-Fol, 1942 (1862)
              • Family Laginiopsidae Pruvot-Fol, 1922
        • Order Runcinida, without differentiation between head and body.
          • Superfamily Runcinoidea H. Adams & A. Adams, 1854
            • Family Ilbiidae Burn, 1963
            • Family Runcinidae H. Adams & A. Adams, 1854
        • Superorder Sacoglossa
          • Superfamily Oxynooidea Stoliczka, 1868 (1847)
            • Family Cylindrobullidae Thiele, 1931
            • Family Juliidae E. A. Smith, 1885
            • Family Oxynoidae Stoliczka, 1868 (1847)
            • Family Volvatellidae Pilsbry, 1895
          • Superfamily Plakobranchoidea Gray, 1840
            • Family Costasiellidae K. B. Clark, 1984
            • Family Hermaeidae H. Adams & A. Adams, 1854
            • Family Limapontiidae Gray, 1847
            • Family Plakobranchidae Gray, 1840
          • Superfamily Platyhedyloidea Salvini-Plawen, 1973
            • Family Platyhedylidae Salvini-Plawen, 1973
        • Order Umbraculida, former Notaspideans
          • Superfamily Umbraculoidea Dall, 1889 (1827)
            • Family Tylodinidae Gray, 1847
            • Family Umbraculidae Dall, 1889 (1827)
        • Superorder Eupulmonata, this superorder and the following groups includes species of snails and slugs, preferably terrestrial or freshwater, hermaphroditic and whose pallial cavity has become a lung without gills whose epithelium exchanges gases with the outside.
        • Superorder Hygrophila
        • Superorder Pylopulmonata
        • Superorder Siphonarimorpha
        • Order Tectibranchiata
      • Superorder [unassigned] Euthyneura includes those species that could not be clearly assigned to other groups.

Jörger et al. (2010) carried out a phylogenetic analysis of the small group of Acochlidia to investigate their origin and their relationships with the other Heterobranchia groups. After a short time, Schrödl et al. (2011) analyzed the phylogeny of the Euthyneura based on molecular analysis and obtained results that substantially modified the established taxonomic and phylogenetic schemes. These works were the trigger -taking advantage of the great advances in molecular techniques and their popularization- that started the long journey of discovering the relationships among these gastropods in the last decade.

Due to the complexity of the problem, we must emphasize that there are still doubts in many points of the phylogenetic cladogram, more molecular analysis are necessary to confirm or discard previous statements. The latest published works, such as Bouchet et al. (2017) try to synthesize and consolidate all the researcher’s discoveries in this complex matter, of which the “last say” has not been said… yet.

The “classic” taxonomic classification, considered valid until the work by Bouchet et Rocroi (2005) can be found here:


    Bouchet, P., and J. P. Rocroi. 2005. Classification and nomenclator of gastropod families. Malacologia. 47: 1–397.
    Bouchet, P., J. P. Rocroi, B. Hausdorf, A. Kaim, Y. Kano, A. Nützel, P. Parkhaev, M. Schrödl, and E. Strong. 2017. Revised classification, nomenclator and typification of gastropod and monoplacophoran families. Malacologia. 61: 1–526.
    Cella, K., L. Carmona, I. Ekimova, A. Chichvarkhin, D. Schepetov, and T. M. Gosliner. 2016. A Radical Solution: The Phylogeny of the Nudibranch Family Fionidae. PLoS ONE 12/2016; 11(12):e0167800.
    Cervera, J. L., G. Calado, C. Gavaia, M. A. E. Malaquías, J. Templado, M. Ballesteros, J. C. García-Gómez, and C. Megina. 2004. An annotated and updated checklist of the opisthobranchs (Mollusca: Gastropoda) from Spain and Portugal (including islands and archipelagos). Boletín Instituto Español de Oceanografía, 20 (1-4): 1-111. L.
    Costello, M. L., C. S. Emblow, and R. (Eds. ) White. 2001. European register of marine species. A check-list of the marine species in Europe and bibliography of guides to their identification. Patrimoines Naturels, 50. Publications Scientifiques du Muséum National d’Histoire Naturelle, Paris.
    Furfaro, G., D. Salvi, E. Mancini, and P. Mariottini. 2018. A multilocus view on Mediterranean aeolid nudibranchs (Mollusca): Systematics and cryptic diversity of Flabellinidae and Piseinotecidae. Molecular Phylogenetics and Evolution. 118: 13–22.
    Goodheart, J., A. L. Bazinet, A. G. Collins, and M. P. Cummings. 2015. Relationships within Cladobranchia (Gastropoda: Nudibranchia) based on RNA-Seq data: an initial investigation. R. Soc. open sci.2: 150196.
    Grande, C., J. Templado, J. L. Cervera, and R. Zardoya. 2004. Phylogenetic relationships among Opisthobranchia (Mollusca : Gastropoda) based on mitochondrial cox 1, trnV, and rrnL genes. Molecular Phylogenetics and Evolution. 33: 378–388.
    Grande, C., J. Templado, J. L. Cervera, and R. Zardoya. 2003. Molecular phylogeny of Euthyneura (Mollusca: Gastropoda). Molecular Biology and Evolution 21 (2): 303-313. 21: 303–313.
    Haszprunar, G. 1985. The Heterobranchia: a new concep of the phylogeny of the higher Gastropoda. Zeitschrift Fur Zoologische Systematik Und Evolutionsforschung. 23: 15–37.
    Jensen, K. R. 1997. Evolution of the Sacoglossa (Mollusca, Opisthobranchia) and the ecological associations with their food plants. Evolutionary Ecology. 11: 301–335.
    Jörger, K. M., I. Stöger, Y. Kano, H. Fukuda, T. Knebelsberger, and M. Schrödl. 2010. On the origin of Acochlidia and other enigmatic euthyneuran gastropods, with implications for the systematics of Heterobranchia. BMC Evolutionary Biology. 10.
    Knudsen, B., B. Kohn, B. Nahir, S. McFadden, and L. L. Moroz. 2006. Complete DNA sequence of the mitochondrial genome of the sea-slug, Aplysia californica: conservation of the gene order in Euthyneura. Molecular Phylogenetics & Evolution. 38 (2): 459–469.
    Korshunova, T. A., A. V. Martynov, T. Bakken, J. Evertsen, K. Fletcher, I. W. Mundiata, H. Saito, K. Lundin, M. Schrödl, and B. Picton. 2017. Polyphyly of the traditional family Flabellinidae affects a major group of Nudibranchia: aeolidacean taxonomic reassessment with descriptions of several new families, genera, and species (Mollusca, Gastropoda). ZooKeys 717: 1-139.
    Korshunova, T. A., A. V. Martynov, T. Bakken, J. Evertsen, K. Fletcher, I. W. Mundiata, H. Saito, K. Lundin, M. Schrödl, and B. Picton. 2017. Corrigenda: Polyphyly of the traditional family Flabellinidae affects a major group of Nudibranchia: aeolidacean taxonomic reassessment with descriptions of several new families, genera, and species (Mollusca, Gastropoda). ZooKeys 725: 139–141.
    Le Renard, J. (Ed. ). 2007. CLEMAM. Check List of European Marine Mollusca. (
    Mahguib, J., and Á. Valdés. 2015. Molecular investigation of the phylogenetic position of the polar nudibranch Doridoxa (Mollusca, Gastropoda, Heterobranchia). Polar Biol (2015) 38:1369–1377.
    Malaquias, M. A. E., J. Mackenzie-Dodds, P. Bouchet, T. M. Gosliner, and D. G. Reid. 2009. A molecular phylogeny of the Cephalaspidea sensu lato (Gastropoda: Euthyneura): Architectibranchia redefined and Runcinacea reinstated. Zoologica Scripta 38(1): 23-41.
    Martínez Cueto-Felgueroso, E. 1995. El orden Anaspidea (Mollusca: Opisthobranchia) en el Atlántico y Mediterráneo próximo: Revisión taxonómica y estudio de los metabolitos secundarios (Tesis Doctoral).
    Milne Edwards, H. 1848. Note sur la classification naturelle des mollusques gasteropodes. Annales des Sciences Naturelles, Paris, series 3, 9:102-112.
    Muchlisin, Z. A., Z. Thomy, N. Fadli, M. A. Sarong, and M. N. Siti-Azizah. 2013. DNA Barcoding of Freshwater Fishes from Lake Laut Tawar, Aceh Province, Indonesia. Acta Ichthyol. Piscat. 43: 21–29.
    Neusser, T. P. 2012. Systematics and Evolution of the Acochlidia (Gastropoda, Euthyneura), a microanatomical approach by means of computer-based 3D reconstruction using Amira.
    Pek, I., Z. Vašíček, Z. Roček, V. Hajn, and R. Mikuláš. 1996. Základy zoopaleontologie. Olomouc.
    Schrödl, M., K. Jörger, A. Klussmann-Kolb, and N. Wilson. 2011. Bye Bye “Opisthobranchia”! a review on the contribution of mesopsammic sea slugs to euthyneuran systematics. Thalassas. 27: 101–112.
    Valdés, Á. 2002. A phylogenetic analysis and systematic revision of the cryptobranch dorids (Mollusca, Nudibranchia, Anthobranchia). Zoological Journal of the Linnean Society 136: 535-636.
    Vonnemann, V., M. Schrodl, A. Klussmann-Kolb, and H. Wägele. 2005. Reconstruction of the phylogeny of the Opisthobranchia (Mollusca : Gastropoda) by means of 18S and 28S rRNA gene sequences. Journal of Molluscan Studies. 71: 113–125.
    Wägele, H., and A. Klussmann Kolb. 2005. Opisthobranchia (Mollusca, Gastropoda) - more than just slimy slugs. Shell reduction and its implications on defence and foraging. Frontiers in Zoology  2(3):1-18.
    Wägele, H., A. Klussmann-Kolb, E. Verbeek, and M. Schrödl. 2014. Flashback and foreshadowing-a review of the taxon Opisthobranchia. Organisms Diversity & Evolution. 14: 133–149.
    WoRMS Editorial Board. 2023. World Register of Marine Species. WoRMS. (
    Zamora-Silva, A., and M. A. E. Malaquias. 2017. Molecular phylogeny of the Aglajidae head-shield sea slugs (Heterobranchia: Cephalaspidea): new evolutionary lineages revealed and proposal of a new classification. Zoological Journal of the Linnean Society, 2017, XX, 1–51.

    Bibliography based on the works by Steve Long, 2006. Bibliography of Opisthobranchia 1554-2000 and Gary McDonald, 2009. Bibliographia Nudibranchia, with later updates from other resources.