Oxynooidea form a superfamily of small and medium-sized nudibranches, with external shell, within the superorder Sacoglossa. There are four families of shelled species: Cylindrobullidae, Volvatellidae, Oxynoidae and Juliidae.

Members of the Juliidae are also known as “bivalved gastropods” because their shells consist of two separate hinged pieces or valves. These valves are joined by a ligament, and do not look like a normal snail shell; instead the valves look almost exactly like the two hinged valves of a clam, also a bivalved mollusk. In the past the Juliidae were known only from fossil shells, but they were classified as a type of mussel, but they are not closely related, it is just a sample of convergent evolution.

The current taxonomy according to Bouchet et al. (2017) and accepted by WoRMS is:

  • Superfamily Oxynooidea Stoliczka, 1868 (1847)
    • Family Cylindrobullidae Thiele, 1931
      • Genus Cylindrobulla P. Fischer, 1857
    • Family Juliidae E. A. Smith, 1885
      • Subfamily Bertheliniinae Keen & A. G. Smith, 1961
        • Genus Berthelinia Crosse, 1875
      • Subfamily Juliinae E. A. Smith, 1885
        • Genus Julia Gould, 1862
    • Family Oxynoidae Stoliczka, 1868 (1847)
      • Genus Lobiger Krohn, 1847
      • Genus Lophopleurella Zilch, 1956
      • Genus Oxynoe Rafinesque, 1814
      • Genus Roburnella Ev. Marcus, 1982
    • Family Volvatellidae Pilsbry, 1895
      • Genus Ascobulla Ev. Marcus, 1972
      • Genus Volvatella Pease, 1860

Species of Oxynooidea reported in the Mediterranean or around the Iberian Peninsula:

Ascobulla fragilis @ Čiovu, Croatia by Pero Ugarković

Ascobulla fragilis

Lobiger serradifalci by Enric Madrenas

Lobiger serradifalci

Oxynoe olivacea

Oxynoe olivacea

Oxynoe viridis by Murat Draman - www.thedivingguidekas.com @ 20090900 Kas, Antalya, Turquia, 25m on Caulerpa racemosa var. lamourouxii

Oxynoe viridis


    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.

    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.