Okenia cf. impexa

Okenia impexa (Marcus Er., 1957)

Okenia impexa by Enric Madrenas

Class: Gastropoda  Cuvier, 1797
Subclass: Heterobranchia  J.E. Gray, 1840
Clade: Euthyneura  Spengel, 1881
Clade: Nudipleura  Wägele & Willan, 2000
Order: Nudibranchia  Cuvier, 1817
Suborder: Euctenidiacea  Tardy, 1970
Infraorder: Doridacea  Thiele, 1931
Superfamily: Onchidoridoidea  J.E. Gray, 1827
Family: Goniodorididae  H. Adams & A. Adams, 1854
Genus: Okenia  Menke, 1830
Species: Okenia impexa (Marcus Er., 1957)

This is a species whose specimens rarely exceed 4-5 mm in length. The body is high and relatively wide. The general body color is hyaline white, sometimes with yellowish or cream tones, while internal organs can be seen by transparency inside of the body. There are numerous dark brown scores scattered throughout the body that may form, in some specimens, a big dark stain in the center of the back. The head has a slightly lobed frontal veil with 4 thin and long tentacular processes. The rhinophores are thick and have up to 8 lamellae that cover the rear and lateral areas of the rhinophore but not the front area. The edge of the dorsum has 6 papillae on each side, elongated and enlarged in a bulbous shape near the apex. The last two papillae on each side grow from a common base. There is also an odd papilla in the center of the back, just in front of the gill. The papillae are coloured in a lighter shade than the body. Gill consists of three unipinnate leaves surrounding the anal papilla. The foot is wide and pointed on the rear side and the mouth and has two rounded bumps on each side.

This rare species has been cited on algae of the genus Halimeda and other coralline algae (Schmekel, 1979), on masses of floating algae in the Atlantic and on the bryozoan Margaretta cereoides, that could be its prey (Ortea et al. 2009). The spawn consists on a bean-shaped mass of 3 mm in length, containing about 500 white eggs (Eyster, 1980).


  • Okenia. In honor of Prof. Dr. Ludwig Gilbert Lorenz Oken, (1779-1851), German natural philosopher, editor of the magazine “Isis” and publisher of the book “Lehrbuch der Naturgeschichte”.
  • Impexa. From Latin “impexus”, uncombed.

Okenia impexa is an amfiatlantic species because since its description by Ernst Marcus in 1957 for Brazilian waters, it has been observed in North Carolina, in Cuba, Puerto Rico and Cape Verde (Valdes & Ortea, 1995), also in the Canary Islands (Ortea et al. 2009). In the Mediterranean Sea it has been cited first by Schmekel (1979) off the coast of Banyuls and Naples, and since then it has only been cited in the Catalan coast: L’Escala, Aiguafreda and Cala Margarida (OPK). It’s not clear whether the Mediterranean specimens are of the same species as the Atlantic ones (Pola, M. pers. comm. 10/12/2016).

Known georeferenced records of the species: Okenia cf. impexa
: GROC 2010-2011
: Enric Madrenas
: João Pedro Silva
: Bernard Picton
: Manuel Ballesteros.
: M@re Nostrum
: Altres fonts
: Marine Regions


    Western Mediterranean:
    Eastern Mediterranean:
    Atlantic Ocean:
This chart displays the observation probability for Okenia cf. impexa based on our own records.

More pictures


Further reading

Cite this article as:

Ballesteros, Manuel, Enric Madrenas, Miquel Pontes et al. (2012-2017) "Okenia cf. impexa" in OPK-Opistobranquis, Published: 24/05/2012, Accessed: 18/12/2017 at (https://opistobranquis.info/en/ucEtT)

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