Nudibranchia

These opisthobranchs are commonly called sea slugs and present a naked body as adult individuals lack a shell. However, their larvae do have an embryonic shell that disappears during metamorphosis. Nudibranchs size can vary from a few mm to about 40 cm in length. Their body shape is highly variable depending on the groups, and could be more or less flattened dorsally as in doridaceans, narrow and elongated as in the aeolidaceans or many other shapes. There are always a couple of sensory tentacles, the rhinophores, on the back of the head. They lack a mantle cavity, so the respiratory structures available to nudibranchs are not similar to those of other mollusks, as they are secondary gills formed later, during the evolution of the group. The gills are directly exposed to the environment, a fact referred to by the name of this group of opisthobranchs: “nudibranch” means “naked gills”. Gills can be dendritic or lamellar and the dorsal digitiform papillae of the aeolidaceans may also act as gills. In many doridaceans the gill if formed by different gill sheets and can be retracted completely into a cavity in the rear of the body.

Felimare tricolor by Enric Madrenas

Most Nudibranchs are benthic (but Glaucus atlanticus and a few more that are pelagic), crawling with their muscular foot and they all are carnivores, some very specialized, which feed mainly on sponges, cnidarians and bryozoans, some species eat eggs of other nudibranchs and a few are even cannibals that can prey on to other smaller nudibranchs. Except for a few exceptions, nudibranchs have a radula that can have multiple teeth, or only one, in a row. They may also have a buccal lip armed with denticles (labial armor) or chitinous jaws with a cutting edge. Despite the lack of shell they have few predators because they are very well defended by different mechanisms, such as homochromy with the substrate, disruptive coloration, presence of spicules in the body tissues, bad taste, secretion of acid substances or different defensive chemicals that are expelled out when disturbed. These powerful body defenses allow many species, such as the Chromodorididae family, to display flashy colorations called warning or aposematic, so these mollusks are placed on top of the list in terms of chromatic beautifulness within marine invertebrates. Nudibranchs, like the rest of opisthobranchs, are hermaphrodites, have internal fertilization by crossed copulation and lay their eggs in the shape of a spiral wound tape or cord. Some species have direct development but most have veliger larvae that swim and feed in the plankton prior to the metamorphosis, when they fall to the sea floor.

Classification
Traditionally, nudibranchs have been classified into four groups, according to their body shape, the position of the anal opening, the structure of the digestive gland and the presence or absence of defined gill structures: the groups are Doridaceans (Doridoidei), Aeolidaceans (Aeolidioidea), Dendronotaceans (Dendronotoidea) and Arminaceans (Arminoidea). The Doridaceans are nudibranchs with a compact digestive gland (holohepatic nudibranchs), which is unbranched, the anus is located in the dorsal middle position and they have dendritic-like gills. Other nudibranchs have branched digestive gland (cladohepatic nudibranchs), that sometimes penetrates the body dorsal papillae, the anus is lateral and the gills are not dendritic. The latest data provided by the molecular phylogeny (not yet definitely solved in some nudibranchs taxa) have clarified the relationships among different groups of nudibranchs. According to these studies (which are accepted in the WoRMS) Nudibranchs are divided into two groups or clades, which could be considered as Suborders, that of Doridina and the Cladobranchia.

The Doridina comprises those holohepatic nudibranchs that have a gill formed by dendritic branchial leaves.

The Cladobranchia includes all other nudibranchs, the classic cladohepatic plus the enigmatic group of Doridoxidae, all of them with the anus in lateral right position and a more or less branched digestive gland.

The systematic synopsis Nudibranchs according to Bouchet et al. (2017) and published at WoRMS is as follows:

  • Order Nudibranchia Cuvier, 1817
    • Suborder Doridina
      • Infraorder Doridoidei
        • Superfamily Doridoidea Rafinesque, 1815
          • Family Discodorididae Bergh, 1891
            • Genus Alloiodoris Bergh, 1904
            • Genus Aporodoris Ihering, 1886
            • Genus Argus Bohadsch, 1761
            • Genus Asteronotus Ehrenberg, 1831
            • Genus Atagema Gray, 1850
            • Genus Baptodoris Bergh, 1884
            • Genus Carminodoris Bergh, 1889
            • Genus Diaulula Bergh, 1878
            • Genus Dictyodoris Bergh, 1880
            • Genus Discodoris Bergh, 1877
            • Genus Gargamella Bergh, 1894
            • Genus Geitodoris Bergh, 1891
            • Genus Gravieria Vayssiere, 1912
            • Genus Halgerda Bergh, 1880
            • Genus Hiatodoris Dayrat, 2010
            • Genus Hoplodoris Bergh, 1880
            • Genus Jorunna Bergh, 1876
            • Genus Nirva Bergh, 1905
            • Genus Nophodoris Valdés & Gosliner, 2001
            • Genus Paradoris Bergh, 1884
            • Genus Peltodoris Bergh, 1880
            • Genus Peronodoris Bergh, 1904
            • Genus Platydoris Bergh, 1877
            • Genus Rostanga Bergh, 1879
            • Genus Sclerodoris Eliot, 1904
            • Genus Sebadoris Er. Marcus & Ev. Marcus, 1960
            • Genus Taringa Er. Marcus, 1955
            • Genus Tayuva Er. Marcus & Ev. Marcus, 1967
            • Genus Thordisa Bergh, 1877
            • Genus Thorybopus Bouchet, 1977
          • Family Dorididae Rafinesque, 1815
            • Genus Aphelodoris Bergh, 1879
            • Genus Artachaea Bergh, 1881
            • Genus Conualevia Collier & Farmer, 1964
            • Genus Doriopsis Pease, 1860
            • Genus Doris Linnaeus, 1758
            • Genus Goslineria Valdés, 2001
            • Genus Pharodoris Valdés, 2001
            • Subfamily Miamirinae Bergh, 1891
        • Superfamily Chromodoridoidea Bergh, 1891
          • Family Actinocyclidae O’Donoghue, 1929
            • Genus Actinocyclus Ehrenberg, 1831
            • Genus Hallaxa Eliot, 1909
          • Family Cadlinidae Bergh, 1891
            • Genus Aldisa Bergh, 1878
            • Genus Cadlina Bergh, 1879
          • Family Chromodorididae Bergh, 1891
            • Genus Ardeadoris Rudman, 1984
            • Genus Berlanguella Ortea, Bacallado & Valdés, 1992
            • Genus Cadlinella Thiele, 1931
            • Genus Ceratosoma A. Adams & Reeve, 1850
            • Genus Chromodoris Alder & Hancock, 1855
            • Genus Diversidoris Rudman, 1987
            • Genus Doriprismatica d’Orbigny, 1839
            • Genus Felimare Ev. Marcus & Er. Marcus, 1967
            • Genus Felimida Ev. Marcus, 1971
            • Genus Glossodoris Ehrenberg, 1831
            • Genus Goniobranchus Pease, 1866
            • Genus Hypselodoris Stimpson, 1855
            • Genus Mexichromis Bertsch, 1977
            • Genus Miamira Bergh, 1874
            • Genus Thorunna Bergh, 1878
            • Genus Tyrinna Bergh, 1898
            • Genus Verconia Pruvot-Fol, 1931
          • Family Hexabranchidae Bergh, 1891
            • Genus Hexabranchus Ehrenberg, 1828
        • Superfamily Onchidoridoidea Gray, 1827
          • Family Aegiridae P. Fischer, 1883
            • Genus Aegires Lovén, 1844
            • Genus Notodoris Bergh, 1875
          • Family Akiodorididae Millen & Martynov, 2005
            • Genus Akiodoris Bergh, 1879
            • Genus Armodoris Minichev, 1972
            • Genus Doridunculus G.O. Sars, 1878
            • Genus Echinocorambe Valdés & Bouchet, 1998
            • Genus Prodoridunculus Thiele, 1912
          • Family Calycidorididae Roginskaya, 1972
            • Genus Calycidoris Abraham, 1876
            • Genus Diaphorodoris Iredale & O’Donoghue, 1923
          • Family Corambidae Bergh, 1871
            • Genus Corambe Bergh, 1869
            • Genus Loy Martynov, 1994
            • Genus Hypobranchiaea A. Adams, 1847 (taxon inquirendum)
          • Family Goniodorididae H. Adams & A. Adams, 1854
            • Genus Ancula Lovén, 1846
            • Genus Goniodoridella Pruvot-Fol, 1933
            • Genus Goniodoris Forbes & Goodsir, 1839
            • Genus Lophodoris G.O. Sars, 1878
            • Genus Murphydoris Sigurdson, 1991
            • Genus Okenia Menke, 1830
            • Genus Spahria Risbec, 1928
            • Genus Trapania Pruvot-Fol, 1931
          • Family Onchidorididae Gray, 1827
            • Genus Acanthodoris Gray, 1850
            • Genus Adalaria Bergh, 1878
            • Genus Knoutsodonta Hallas & Gosliner, 2015
            • Genus Onchidoris Blainville, 1816
            • Genus Onchimira Martynov, Korshunova, Sanamyan N. & Sanamyan K., 2009
        • Superfamily Phyllidioidea Rafinesque, 1814
          • Family Dendrodorididae O’Donoghue, 1924 (1864)
            • Genus Cariopsilla Ortea & Espinosa, 2006
            • Genus Dendrodoris Ehrenberg, 1831
            • Genus Doriopsilla Bergh, 1880
          • Family Mandeliidae Valdés & Gosliner, 1999
            • Genus Mandelia Valdés & Gosliner, 1999
          • Family Phyllidiidae Rafinesque, 1814
            • Genus Ceratophyllidia Eliot, 1903
            • Genus Phyllidia Cuvier, 1797
            • Genus Phyllidiella Bergh, 1869
            • Genus Phyllidiopsis Bergh, 1876
            • Genus Reticulidia Brunckhorst, 1990
        • Superfamily Polyceroidea Alder & Hancock, 1845
          • Family Polyceridae Alder & Hancock, 1845
            • Subfamily Kalinginae Pruvot-Fol, 1956
              • Genus Kalinga Alder & Hancock, 1864
            • Subfamily Kankelibranchinae Ortea, Espinosa & Caballer, 2005
              • Genus Kankelibranchus Ortea, Espinosa & Caballer, 2005
            • Subfamily Nembrothinae Burn, 1967
              • Genus Martadoris Willan & Chang, 2017
              • Genus Nembrotha Bergh, 1877
              • Genus Roboastra Bergh, 1877
              • Genus Tambja Burn, 1962
              • Genus Tyrannodoris Willan & Chang, 2017
            • Subfamily Polycerinae Alder & Hancock, 1845
              • Genus Greilada Bergh, 1894
              • Genus Palio Gray, 1857
              • Genus Polycera Cuvier, 1816
              • Genus Polycerella A. E. Verrill, 1880
              • Genus Thecacera Fleming, 1828
            • Subfamily Triophinae Odhner, 1941
              • Genus Colga Bergh, 1880
              • Genus Crimora Alder & Hancock, 1862
              • Genus Heteroplocamus W. R. B. Oliver, 1915
              • Genus Holoplocamus Odhner, 1926
              • Genus Joubiniopsis Risbec, 1928
              • Genus Kaloplocamus Bergh, 1880
              • Genus Limacia O. F. Müller, 1781
              • Genus Plocamopherus Rüppell & Leuckart, 1828
              • Genus Triopha Bergh, 1880
        • Superfamily unassigned Doridoidei 
          • Family Okadaiidae Baba, 1930
            • Genus Vayssierea Risbec, 1928
      • Infraorder Bathydoridoidei
        • Superfamily Bathydoridoidea Bergh, 1891
          • Family Bathydorididae Bergh, 1891
            • Genus Bathydoris Bergh, 1884
            • Genus Doriodoxa Bergh, 1899
            • Genus Prodoris Baranetz & Minichev, 1995
    • Suborder Cladobranchia
      • Superfamily Aeolidioidea Gray, 1827
        • Family Aeolidiidae Gray, 1827
          • Genus Aeolidia Cuvier, 1798
          • Genus Aeolidiella Bergh, 1867
          • Genus Anteaeolidiella M. C. Miller, 2001
          • Genus Baeolidia Bergh, 1888
          • Genus Berghia Trinchese, 1877
          • Genus Bulbaeolidia Carmona, Pola, Gosliner & Cervera, 2013
          • Genus Cerberilla Bergh, 1873
          • Genus Limenandra Haefelfinger & Stamm, 1958
          • Genus Spurilla Bergh, 1864
          • Genus Zeusia Korshunova, Zimina & Martynov, 2017
        • Family Babakinidae Roller, 1973
          • Genus Babakina Roller, 1973
        • Family Facelinidae Bergh, 1889
          • Genus Adfacelina Millen & Hermosillo, 2012
          • Genus Algarvia Garcia-Gomez & Cervera, 1990
          • Genus Amanda Macnae, 1954
          • Genus Anetarca Gosliner, 1991
          • Genus Antonietta Schmekel, 1966
          • Genus Austraeolis Burn, 1962
          • Genus Bajaeolis Gosliner & Behrens, 1986
          • Genus Burnaia M. C. Miller, 2001
          • Genus Caloria Trinchese, 1888
          • Genus Cratena Bergh, 1864
          • Subfamily Crateninae Bergh, 1889
            • Genus Echinopsole Macnae, 1954
            • Genus Emarcusia Roller, 1972
            • Genus Facelina Alder & Hancock, 1855
          • Subfamily Facelininae Bergh, 1889
            • Genus Facelinopsis Pruvot-Fol, 1954
          • Subfamily Favorininae Bergh, 1889
            • Genus Dicata Schmekel, 1967
            • Genus Dondice Marcus, 1958
            • Genus Godiva Macnae, 1954
            • Genus Favorinus Gray, 1850
            • Genus Hermissenda Bergh, 1879
            • Genus Hermosita Gosliner & Behrens, 1986
            • Genus Herviella Baba, 1949
          • Subfamily Herviellinae Burn, 1967
            • Genus Jason M. C. Miller, 1974
            • Genus Learchis Bergh, 1896
            • Genus Moridilla Bergh, 1888
            • Genus Nanuca Marcus, 1957
            • Genus Noumeaella Risbec, 1937
            • Genus Palisa Edmunds, 1964
            • Genus Pauleo Millen & Hamann, 1992
            • Genus Phidiana Gray, 1850
            • Genus Phyllodesmium Ehrenberg, 1831
            • Genus Pruvotfolia Tardy, 1969
            • Genus Pteraeolidia Bergh, 1875
          • Subfamily Pteraeolidiinae Risbec, 1953
            • Genus Sakuraeolis Baba, 1965
            • Genus Setoeolis Baba & Hamatani, 1965
        • Family Glaucidae Gray, 1827
          • Genus Glaucus Forster, 1777
        • Family Piseinotecidae Edmunds, 1970
          • Genus Piseinotecus Er. Marcus, 1955
        • Family Pleurolidiidae Burn, 1966
          • Genus Pleurolidia Burn, 1966
          • Genus Protaeolidiella Baba, 1955
        • Family Unidentiidae Millen & Hermosillo, 2012
          • Genus Pacifia Korshunova, Martynov, Bakken, Evertsen, Fletcher, Mudianta, Saito, Lundin, Schrödl & Picton, 2017
          • Genus Unidentia Millen & Hermosillo, 2012
      • Superfamily Arminoidea Iredale & O’Donoghue, 1923 (1841)
        • Family Arminidae Iredale & O’Donoghue, 1923 (1841)
          • Genus Armina Rafinesque, 1814
          • Genus Atthila Bergh, 1899
          • Genus Dermatobranchus van Hasselt, 1824
          • Genus Heterodoris Verrill & Emerton, 1882
          • Genus Histiomena Mörch, 1860
          • Genus Pleurophyllidiella Eliot, 1903
          • Genus Pleurophyllidiopsis Tchang, 1934
        • Family Doridomorphidae Er. Marcus & Ev. Marcus, 1960 (1908)
          • Genus Doridomorpha Eliot, 1903
      • Superfamily Dendronotoidea Allman, 1845
        • Family Dendronotidae Allman, 1845
          • Genus Dendronotus Alder & Hancock, 1845
        • Family Dotidae Gray, 1853
          • Genus Caecinella Bergh, 1870
          • Genus Doto Oken, 1815
          • Genus Kabeiro Shipman & Gosliner, 2015
          • Genus Miesea Er. Marcus, 1961
        • Family Hancockiidae MacFarland, 1923
          • Genus Hancockia Gosse, 1877
        • Family Scyllaeidae Alder & Hancock, 1855
          • Genus Crosslandia Eliot, 1902
          • Genus Notobryon Odhner, 1936
          • Genus Scyllaea Linnaeus, 1758
        • Family Tethydidae Rafinesque, 1815
          • Genus Melibe Rang, 1829
          • Genus Tethys Linnaeus, 1767
      • Superfamily Doridoxoidea Bergh, 1899
        • Family Doridoxidae Bergh, 1899
          • Genus Doridoxa Bergh, 1899
      • Superfamily Fionoidea Gray, 1857
        • Family Abronicidae Korshunova et al 2017
          • Genus Abronica Cella, Carmona, Ekimova, Chichvarkhin, Schepetov & Gosliner, 2016
        • Family Calmidae Iredale & O’Donoghue, 1923
          • Genus Calma Alder & Hancock, 1855
        • Family Cuthonellidae Miller, 1971
          • Genus Cuthonella Bergh, 1884
        • Family Cuthonidae Odhner, 1934
          • Genus Cuthona Alder & Hancock, 1855
        • Family Eubranchidae Odhner, 1934
          • Genus Eubranchus Forbes, 1838
          • Genus Leostyletus Martynov, 1998
        • Family Fionidae Gray, 1857
          • Genus Fiona Alder & Hancock [in Forbes & Hanley], 1853
          • Genus Tergiposacca Cella, Carmona, Ekimova, Chichvarkhin, Schepetov & Gosliner, 2016
          • Genus Zatteria Eliot, 1902
        • Family Lomanotidae Bergh, 1890
          • Genus Lomanotus Vérany, 1844
        • Family Murmaniidae Korshunova et al 2017
          • Genus Murmania Martynov, 2006
        • Family Pinufiidae Er. Marcus & Ev. Marcus, 1960
          • Genus Pinufius Er. Marcus & Ev. Marcus, 1960
        • Family Tergipedidae Bergh, 1889
          • Genus Tergipes Cuvier, 1805
        • Family Trinchesiidae F. Nordsieck, 1972
          • Genus Catriona Winckworth, 1941
          • Genus Diaphoreolis Iredale & O’Donoghue, 1923
          • Genus Phestilla Bergh, 1874
          • Genus Rubramoena Cella, Carmona, Ekimova, Chichvarkhin, Schepetov & Gosliner, 2016
          • Genus Selva Edmunds, 1964
          • Genus Tenellia A. Costa, 1866
          • Genus Trinchesia Ihering, 1879
          • Genus Zelentia Korshunova, Martynov & Picton, 2017
      • Superfamily Flabellinoidea Bergh, 1889
        • Family Apataidae Korshunova et al 2017
          • Genus Apata Korshunova et al 2017
          • Genus Tularia Burn, 1966
        • Family Coryphellidae Bergh, 1889
          • Genus Borealea Korshunova et al 2017
          • Genus Coryphella M. E. Gray, 1850
          • Genus Fjordia Korshunova et al 2017
          • Genus Gulenia Korshunova et al 2017
          • Genus Himatina Thiele, 1931
          • Genus Itaxia Korshunova et al 2017
          • Genus Microchlamylla Korshunova et al 2017
          • Genus Occidenthella Korshunova et al 2017
          • Genus Orienthella Korshunova et al 2017
        • Family Cumanotidae Odhner, 1907
          • Genus Cumanotus Odhner, 1907
        • Family Flabellinidae Bergh, 1889
          • Genus Calmella Eliot, 1910
          • Genus Carronella Korshunova et al 2017
          • Genus Coryphellina O’Donoghue, 1929
          • Genus Edmundsella Korshunova et al 2017
          • Genus Flabellina Gray, 1833
          • Genus Paraflabellina Korshunova et al 2017
        • Family Flabellinopsidae Korshunova et al 2017
          • Genus Baenopsis Korshunova et al 2017
          • Genus Flabellinopsis MacFarland, 1966
        • Family Notaeolidiidae Eliot, 1910
          • Genus Notaeolidia Eliot, 1905
        • Family Paracoryphellidae M. C. Miller, 1971
          • Genus Chlamylla Bergh, 1886
          • Genus Paracoryphella M. C. Miller, 1971
          • Genus Polaria Korshunova et al 2017
          • Genus Ziminella Korshunova et al 2017
        • Family Samlidae Korshunova et al 2017
          • Genus Luisella Korshunova et al 2017
          • Genus Samla Bergh, 1900
      • Superfamily Proctonotoidea Gray, 1853
        • Family Curnonidae d’Udekem d’Acoz, 2017
          • Genus Curnon d’Udekem d’Acoz, 2017
          • Genus Pseudotritonia Thiele, 1912
        • Family Dironidae Eliot, 1910
          • Genus Dirona MacFarland, 1905
        • Family Lemindidae Griffiths, 1985
          • Genus Leminda Griffiths, 1985
        • Family Proctonotidae Gray, 1853
          • Genus Bonisa Gosliner, 1981
          • Genus Caldukia Burn & M. C. Miller, 1969
          • Genus Galeojanolus M. C. Miller, 1971
          • Genus Janolus Bergh, 1884
          • Genus Proctonotus Alder & Hancock, 1844
      • Superfamily Tritonioidea Lamarck, 1809
        • Family Tritoniidae Lamarck, 1809
          • Genus Marianina Pruvot-Fol, 1931
          • Genus Marionia Vayssière, 1877
          • Genus Marioniopsis Odhner, 1934
          • Genus Paratritonia Baba, 1949
          • Genus Tochuina Odhner, 1963
          • Genus Tritonia Cuvier, 1798
          • Genus Tritonidoxa Bergh, 1907
          • Genus Tritoniella Eliot, 1907
          • Genus Tritoniopsis Eliot, 1905
      • Superfamily Unassigned Cladobranchia
        • Family Bornellidae Bergh, 1874
          • Genus Bornella Gray, 1850
          • Genus Bornellopsis O’Donoghue, 1929
        • Family Embletoniidae Pruvot-Fol, 1954
          • Genus Embletonia Alder & Hancock, 1851
        • Family Goniaeolididae Odhner, 1907
          • Genus Goniaeolis M. Sars, 1861
        • Family Heroidae Gray, 1857
          • Genus Hero Alder & Hancock, 1855
        • Family Madrellidae Preston, 1911
          • Genus Eliotia Vayssière, 1909
          • Genus Madrella Alder & Hancock, 1864
        • Family Phylliroidae Menke, 1830
          • Genus Cephalopyge Hanel, 1905
          • Genus Phylliroe Péron & Lesueur, 1810
        • Family Pseudovermidae Thiele, 1931
          • Genus Pseudovermis Perejaslavtzeva, 1891
        • Genus Trivettea Bertsch, 2014

Main nudibranch suborders:

Peltodoris atromaculata

Doridina

Janolus cristatus by Enric Madrenas

Cladobranchia

Bibliography