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 Enrico Ricchitelli

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